Current Diagnosis and Treatment in Orthopedics, 4th Edition
Chapter 5. Disorders, Diseases, & Injuries of the Spine
OSTEOMYELITIS OF THE SPINE
Osteomyelitis of the spine comprises approximately 1% of all cases of pyogenic skeletal infections. Pathogenic organisms can infect the vertebra, the intervertebral disk, or the spinal canal through multiple mechanisms, including local spread from an adjacent infection or as a result of seeding from a noncontiguous source of infection either hematogenously or through the lymphatics. Bacteria can also be introduced directly to compromised tissues as a result of trauma, surgery, diskography, or intravenous or intradural catheterization. Although many organisms are implicated, the most frequently cultured organisms are Staphylococcus aureus and Pseudomonas aeruginosa. Salmonella should be strongly considered as a potential pathogen in patients with sickle cell disease. Infection with Mycobacterium tuberculosis is often seen in less developed countries and in prison populations. Spinal sepsis is most common in adolescents, the elderly (more than 60 years), intravenous drug abusers, patients with diabetes or renal failure, and patients who have undergone spinal surgery. Osteoporosis is also implicated as a predisposing factor secondary to increased blood flow. Eismont and Bohlman reported several risk factors for neurologic deterioration including patients with diabetes, rheumatoid arthritis, steroid use, age greater than 50 years, a cephalad level of infection, and infection with S. aureus. For additional information on osteomyelitis, see Chapter 8.
SYMPTOMS AND SIGNS
Patients with osteomyelitis of the spine may or may not present with symptoms relating to their spine. Pyogenic osteomyelitis is fundamentally different from tubercular osteomyelitis. In the latter, patients generally complain of indolent, chronic back pain. In pyogenic osteomyelitis, the symptoms of acute spontaneous back pain, fever, and weight loss are common but not always present. On physical examination, patients with diskitis or pyogenic osteomyelitis of the spine often exhibit significant percussion tenderness posteriorly over the affected vertebral segments. Paraspinal muscle spasm may be seen in more than 90% of patients. A history of fevers is found in less than 50% of affected patients. Neurologic involvement, fortunately, affects less than 10% of all patients with spinal infections. When the infection involves the cervical spine, patients may develop Horner syndrome, or dysphagia. Pyogenic osteomyelitis should be suspected in any patient who presents with back pain and a recent history of an acute systemic infection (eg, appendicitis, perinephritic abscess, pneumonia, genitourinary tract infection, or meningitis).
The results of laboratory tests can be equivocal. The white cell count is elevated in only 42% of patients and often is normal. Both blood and spinal cultures may also be negative. Blood cultures are accurate in only 25% of cases, and closed biopsy techniques are diagnostic in only 70% of cases. The ESR rate is elevated in more than 90% of patients, and the C-reactive protein level (CRP) is also elevated at an earlier point in the infectious process. However, both of these tests are systemic indicators of inflammation and are relatively nonspecific. Thus, there is often a significant delay in diagnosis because many of the signs and symptoms of pyogenic vertebral osteomyelitis are subtle. Clearly, the diagnosis relies on having a high index of suspicion in at-risk patients as well as initiating the appropriate evaluation that will identify the organism and determine the extent of infection.
Radiographic signs of osteomyelitis typically lag behind symptomatic progression of the disease. MRI with vascular-based contrast enhancement (gadolinium) is the gold standard for early neurodiagnostic imaging. Radiographic findings may appear normal.
In pyogenic osteomyelitis, early radiographic changes may include loss of disk space height, erosion of the vertebral endplates, and vertebral destruction and collapse (Figure 5–1). In advanced cases, the vertebral bodies may become fused because of the inflammation and destruction of the intervertebral disk.
In tubercular osteomyelitis, radiographic studies typically demonstrate anterior vertebral body destruction with sparing of the intervertebral disk. Loss of bone stability in the cervical or thoracic spine may lead to kyphotic deformity and paralysis. Progression to solid fusion may occur but usually later than seen in pyogenic osteomyelitis.
Early diagnosis and identification of the responsible organism is the cornerstone of treatment. Once the organism is confirmed by biopsy or blood culture, appropriate intravenous antibiotics should be initiated and continued for at least 6 weeks. Short-term bed rest for pain management is appropriate. Spinal column bracing is often necessary for pain relief, immobilization of the affected segments, and minimizing the progression of spinal deformity. Success of nonoperative treatment is linked to patient age younger than 60 years, immunocompetency, infection with S. aureus, and a decreasing erythrocyte sedimentation rate (ESR) with appropriate medical treatment. Indications for surgery other than tissue diagnosis include moderate to advanced destruction of the spine with instability, neurologic compromise, sequestrum formation, and failure to respond to intravenous antibiotics. Paraspinal abscesses may be managed conservatively with intravenous antibiotics unless the patient meets one of the surgical criteria just listed.
Pediatric diskitis often responds to spinal column bracing, immobilization, and rest. Although controversial, antibiotic therapy in the pediatric diskitis patient appears to improve nonoperative resolution of symptoms.
The incidence of epidural abscesses may be on the rise, associated with older patients and chronic illness. Epidural abscesses are best treated with early recognition, antibiotic therapy, and immediate surgical decompression. Preoperative paralysis and neurologic deterioration are poor prognostic factors of the disease. MRI is as sensitive as myelography with CT. For diagnostic purposes, MRI offers the advantage of being noninvasive and being able to delineate other disease entities, making it the imaging modality of choice.
For surgical candidates with osteomyelitis or diskitis, the treatment of choice consists of anterior surgical debridement and stabilization with an autogenous structural graft bone graft. Often posterior instrumentation and spinal fusion over the affected segments is necessary to prevent collapse of the anterior graft and to prevent late deformity. Foreign bodies, such as methylmethacrylate, are relatively contraindicated in spinal stabilization, although newer studies suggest that instrumentation can be safely used in an anterior column infection. Antibiotic-impregnated polymethylmethacrylate (PMMA) cement used as a temporary spacer may be useful in grossly contaminated sites. New minimally invasive surgical techniques that use laparoscopy and thoracoscopy appear to be an excellent alternative for operative management of spinal infections. These techniques employ similar surgical principles with expanding surgeon experience, although currently a thorough decompression of the spinal canal is not possible with the minimally invasive technique.
PRIMARY TUMORS OF THE SPINE
Primary tumors of the spine account for 0.04% of all tumors and 10% of all primary tumors of bone. The overwhelming majority of spinal tumors are metastatic. As with tumors elsewhere in the musculoskeletal system, primary lesions in the spine may be osteogenic, chondrogenic, fibrogenic, hematopoietic, neurogenic, or vascular. Generally, benign tumors typically occur in the younger age group (younger than 21 years), whereas up to 70% of malignant tumors are found in patients older than 21 years.
Principles of Diagnosis
HISTORY AND PHYSICAL EXAMINATION
If the presence of a spinal tumor is suspected, a thorough history and physical examination must be performed. Pain is the common presenting symptom. Persistent pain, especially at night, is the chief complaint in more than 80% of cases. The average time from onset of symptoms until diagnosis in patients with benign lesions is 19 months, whereas that in patients with metastatic disease is 4 months. The age of the patient is important in establishing the differential diagnosis (see Chapter 6). In adults, malignant lesions of bone occur twice as frequently as benign lesions. In children younger than 10 years, however, only 15–20% of tumors are malignant. Location within the spinal column also aids in establishing the diagnosis. Although 75% of tumors located in the vertebral bodies or pedicles are malignant, only 35% of those in the posterior elements are malignant.
On examination, the patient may complain of tenderness over the involved region of the spine. Although rare initially, radiculopathy secondary to nerve root compression may be the only finding. Signs and symptoms may mimic a herniated nucleus pulposus and may progress to localized weakness, sensory loss, and bowel or bladder dysfunction. Up to 70% of patients may develop motor weakness by the time the diagnosis is made. Pathologic fractures may present with acute onset of pain and paraparesis. Examination of the spine may reveal scoliosis, as occurs with osteomas or osteoblastomas, or it may reveal a painful kyphosis.
The workup begins with high-quality plain radiographs, followed by CT scanning, radioisotope bone scanning, and MRI as necessary. The routine anteroposterior view may reveal the presence of the so-called winking owl sign, which is indicative of early pedicle destruction. As with other bony tumors, the more slowly expanding bony tumors of the spine are well circumscribed with reactive ossification. More aggressive lesions have a moth-eaten or erosive appearance. It is important to realize that radiographic evidence of bony destruction is not apparent until 30–50% of the trabecular bone is lost. Vertebral collapse with preservation of the disk space is a common finding.
Early on it is often difficult on plain radiographs to distinguish a neoplastic process from an infectious one. Technetium bone scans are an accurate and sensitive modality in detecting metastatic disease. False-positive results are acceptably low and usually a result of osteoarthritis. If the osteoblastic response is impaired, as in multiple myeloma or in highly lytic lesions, false-negative results may occur. However, with the advent of MRI, bone scanning is limited in its usefulness in staging of the tumor.
CT scanning with or without myelography is of great benefit in detecting and evaluating osseous lesions and dural impingement. CT scanning also allows an accurate assessment of the extent of bony destruction to help in preoperative planning. Evaluation of soft tissue and marrow has improved immensely with the advent of MRI. Tumor resolution is outstanding (Figure 5–2), and preoperative planning is greatly enhanced.
Arteriography enables the surgeon to evaluate the vascular supply to the tumor and the extent of vascular neogenesis. Highly vascular tumors, such as metastatic renal cell tumors, thyroid carcinoma, hemangiosarcoma, and aneurysmal bone cysts, are well visualized. Partial or complete embolization of highly vascular tumors may make operative resection significantly easier and safer. In addition, identification of feeder vessels in tumors in the lower thoracic spine may help identify possible vascular supply to the tumor from the artery of Adamkewitz. Inappropriate ligation of this major vessel may result in spinal cord ischemia and paralysis.
MRI is the study of choice in the diagnosis and evaluation of primary neoplasms of the spine. Its advantages include superior soft-tissue visualization, the availability of multiplanar images, and the ability to evaluate the extent of neural compression or infiltration.
An open or closed percutaneous biopsy may be necessary for establishing the diagnosis. If the workup is consistent with a benign symptomatic tumor such as an osteoid osteoma, an excisional biopsy may be appropriate. When malignancy is suspected, needle biopsy should be performed prior to resection. Because the accuracy rate for needle biopsy is 75% or less, several specimens should be obtained. Open biopsy is necessary if aspiration is nondiagnostic.
The surgical treatment of spinal tumors depends on (1) biologic tumor type, (2) location within spine, (3) percentage of vertebral involvement, (4) neurologic involvement, (5) potential for spine failure and instability, and (6) anticipated life expectancy of the patient.
Benign primary tumors of the spine include osteoid osteoma, osteoblastoma, osteochondroma, aneurysmal bone cyst, hemangioma, eosinophilic granuloma, and giant cell tumor. For additional discussion of these tumors, see Chapter 6.
Osteoid osteoma and osteoblastoma are osteoblastic lesions that are differentiated from each other by size. Lesions smaller than 2 cm are arbitrarily called osteoid osteomas, whereas tumors larger than 2 cm are called osteoblastomas. Osteoid osteoma affects males more frequently than females and is generally seen in patients between 10 and 20 years of age. This benign tumor is usually located in the posterior elements and most frequently involves the lumbar spine, followed by the cervical and then the thoracic spine.
The patient presents with a complaint of a progressive localized ache that may or may not have a radicular component but is usually relieved by the use of salicylates. Tenderness, muscle spasm, neurologic abnormalities, and even scoliosis may be present on examination. Torticollis may be associated with scoliosis of the cervical spine. Pelvic tilt may be seen in conjunction with lumbar spine scoliosis. Minimal correctability is seen with side bending. In the majority of cases, the tumor is located on the concave side of the curve.
Osteoid osteomas appear radiographically as a nidus surrounded by densely sclerotic bone. Tumors that grow close to the periosteum may cause a fusiform thickening of the overlying cortex secondary to hyperemia. Both the nidus and periosteal reaction can sometimes be seen on plain radiographs but are most easily delineated on the axial cuts of a CT scan. Although spontaneous resolution is reported in some cases, treatment of osteoid osteoma generally requires thorough local excision of the lesion because recurrence is likely. Spinal fusion is usually not indicated at the time of excision. In most cases, any scoliosis present preoperatively improves over the following 6–12 months. If the scoliosis is severe (more than 40 degrees) or the spine was rendered unstable by resection of the articular facets and pedicle, fusion should be considered.
When osteoid osteomas grow larger than 2 cm, they are called osteoblastomas. Benign osteoblastomas account for fewer than 1% of all bone tumors. Although cases are rare, more than 40% of them involve the spine, and half of these spinal cases are associated with scoliosis. Osteoblastomas are more common in males than females and seen most frequently in patients younger than 30 years.
Patients generally complain of localized pain or scoliosis. Fifty-three percent of spinal osteoblastomas are found in the lumbar spine, and the rest are equally distributed in the thoracic and cervical spine.
Radiographic examination may reveal an expanded sclerotic cortex, although there are no classic characteristics. Rarely is the lesion lobulated. The posterior elements and pedicles are more frequently involved than the vertebral body. Vertebral involvement almost always occurs because of secondary expansion from the pedicle, and there may be an associated soft-tissue mass.
Curettage can offer a high rate of disease remission when the lesions are well contained within the vertebral bone. Wide excision of the lesion is always curative and may also provide reliable pain relief and resolution of the spinal deformity. However, marginal excision is safer, provides an excellent cure rate, and is the treatment of choice for these tumors. Even partial excision may offer symptom resolution if the nidus is removed. This can be aided by the use of adjuvant radiotherapy. The local recurrence rate can be up to 10% for some osteoblastomas, but malignant degeneration is a rare occurrence.
Osteochondromas result when metaplastic cartilage cells in the periosteum undergo progressive endochondral ossification. Multiple osteochondromatosis is the most common of all skeletal dysplasias, and approximately 7% of these patients have vertebral involvement. Spinal cord compression may occur and is the main indication for excision, which is almost always curative.
Aneurysmal Bone Cyst
Aneurysmal bone cysts result from an expansile hyperemic osteolytic process that erodes through bone. Approximately 80% of patients are younger than 20 years. An estimated 12–30% of these neoplasms occur in the spine, especially the lumbar areas. The tumor involves the posterior elements 60% of the time. Symptoms and signs include a rapid evolution of pain in the spine and radiculopathy. Radiographs reveal the presence of an osteolytic tumor with poor demarcation, peripheral ballooning, and cortical erosion with osseous septa within its substance. Like the chordoma but unlike most other tumors, the aneurysmal bone cyst may cross the intervertebral space. Scoliosis or kyphosis may be present.
The differential diagnosis includes giant cell tumors and cavernous hemangioma. Giant cell tumors usually occur in an older patient population and tend to involve the sacrum. A cavernous hemangioma is usually located in the vertebral body.
Appropriate treatment of aneurysmal bone cysts requires recognition that it may arise from or coexist with a preexisting neoplasm. For the isolated lesion, the treatment of choice is aggressive debulking. If the size and location of the tumor preclude complete surgical removal, incomplete curettage can be undertaken and usually eradicates the lesion. Bone grafting is often necessary. Spinal instrumentation, fusion, or both may be necessary, depending on the extent of the lesion.
Profound hemorrhage is a risk with primary surgical resection and may be controlled with preoperative embolization. Although aneurysmal bone cysts are sensitive to radiation, complications of irradiation-induced myelopathy and sarcoma are noted.
Hemangiomas, common tumors of the vertebral column, arise from embryonic angioblastic tissue. They comprise approximately 7% of all benign tumors. They are much more common in females than in males and have a predilection for the lower thoracic and upper lumbar spine.
Hemangiomas are frequently asymptomatic. In some cases, they are found serendipitously on screening radiographs. In other cases, they are associated with a compression fracture, with the patient presenting with pain and neurologic symptoms. Radiographically, they present with classic vertebral striations resulting from the abnormally thickened bony trabeculae. CT scans easily delineate the lesion, and MRI shows high signal intensity on T2-weighted images and low signal intensity on T1-weighted images. If the patient presents with pain without neurologic deficit, low-dose irradiation is extremely effective in ameliorating the symptoms. If the patient shows signs of neurologic dysfunction, treatment should consist of anterior decompression, mass excision, and anterior fusion. Preoperative embolization of the feeding artery may facilitate surgical management.
Eosinophilic Granuloma (Langerhans Cell Histiocytosis)
Eosinophilic granuloma is a proliferative disorder of the Langerhans cells that is commonly seen in children younger than 10 years and rarely in adults. The disease has a male preponderance. Vertebral involvement is seen in 7–15% of cases and typically presents with a sudden onset of neck pain and torticollis.
Patients frequently present with localized pain. Spinal cord compression is a rare but reported event.
Eosinophilic granuloma can present with a spectrum of radiographic manifestations depending on the stage of the tumor. Early on, the tumor presents as a central lytic lesion with poorly defined margins. On plain radiographs, there is permeative bony destruction with a marked periosteal reaction. At this stage, the tumor is difficult to distinguish from a high-grade sarcoma such as Ewing sarcoma. Later in the evolution of the tumor, there is vertebral body collapse leading to a flattening of the vertebral bone between the adjacent intact disks. This phenomenon results in the classic "coin-on-end" appearance and "vertebra plana."
The differential diagnosis includes Ewing sarcoma and infection, and biopsy may be necessary to confirm the diagnosis.
Eosinophilic granuloma usually resolves spontaneously. If the patient suffers from disseminated Langerhans cell histiocytosis, chemotherapy may be appropriate. Local infiltration with corticosteroids is of some benefit. Low-dose irradiation (500–1000 rads) is used in cases associated with neurologic compromise. The use of anterior decompression and anterior fusion is the treatment of choice in patients with neurologic symptoms.
Giant Cell Tumor
Giant cell tumors comprise approximately 10% of all primary bone tumors. These tumors occur in people between 20 and 40 years of age with a slight female predominance (70.8%). Spinal involvement is seen in patients in the third and fourth decades of life. This tumor is locally aggressive and presents most commonly in the anterior vertebral structures. The presenting complaint is typically pain; however, as many as 50% of patients may present with neurologic deficits. Plain radiographs show a lytic lesion with matrix calcification and sclerosis. Aggressive surgical curettage or en bloc excision depending on the location and extent of tumor yield the best results. Because of the risk of sarcomatous transformation, radiation therapy should be reserved for patients with incomplete excision or local recurrence. There is a higher recurrence rate in those patients with soft-tissue extension, anterior and posterior tumor, and spinal canal involvement.
Primary malignant tumors of the spine are rare and carry a poor prognosis. Multiple myeloma is the most common. Osteosarcoma, Ewing sarcoma, chondrosarcoma, and chordoma occur much less frequently. For additional discussion of these tumors, see Chapter 6.
Solitary Plasmacytoma & Multiple Myeloma
Multiple myeloma and solitary plasmacytoma are B-cell lymphoproliferative diseases composed of abnormal aggregates of plasma cells. The neoplasm has a peak occurrence between 50 and 60 years of age with an equal sex distribution. Multiple myeloma is a multifocal plasma cell cancer of the osseous system whose neoplastic cells produce complete or incomplete immunoglobulins. The annual incidence of myeloma is approximately 2–3 per 100,000 among the general population. Genetic analysis of the tumor cells demonstrates abnormalities in band q32 of chromosome 14. The diagnosis is made on serum and urine evaluation for abnormal immunoglobulin levels. Serum protein electrophoresis shows increases in the levels of one of the immunoglobulin classes. The M-component is IgG in 55% of cases, IgA in 25% of cases, and rarely IgE, IgD, or IgM. Urine protein electrophoresis may detect the presence of immunoglobulin light chains called Bence Jones proteins in up to 99% of patients. In 60% of patients afflicted with multiple myeloma, both Bence Jones proteins and abnormal serum immunoglobulin levels are detected.
The initial treatment of myeloma consists of chemotherapy and irradiation. Chemotherapy is an effective means of controlling the advancement of the disease process but may increase the risk of secondary leukemia. The commonly employed agents include melphalan and prednisone. Newer agents such as gallium nitrate may attenuate the rate of skeletal bone loss from the disease and from steroid treatment. Radiation to affected osseous sites may reduce pain and prevent vertebral collapse, deformity, and neural compression. Patients with solitary plasmacytoma have a 5-year survival rate of 60%. In contrast, patients with multiple myeloma have only an 18% 5-year survival rate and a median survival of 24 months.
Primary osteosarcoma is a malignant tumor of mesenchymal cells characterized by the direct formation of osteoid or bone by the tumor cells. It is the second most common primary neoplasm of bone behind myeloma. Most appear in persons younger than 20 years of age before epiphyseal closure. There is a slight male preponderance. In a series of patients with osteosarcoma, Barwick noted that 1–2% arose initially in the spine.
Patients with retinoblastoma (caused by a hereditary mutation in the q14 band of chromosome 13 that codes for a tumor suppressor gene) have a 500-fold greater risk of developing osteosarcoma. The overall consensus is that these tumors have a multifactorial origin involving genetic, constitutional, and environmental influences.
Radiographically, osteosarcomas present as mixed lytic and sclerotic lesions that cause cortical destruction and soft-tissue calcification. In advanced stages, vertebral collapse occurs from replacement of the structural elements of the spine with tumor. Traditional therapy involved limited tumor resection and radiotherapy. A more aggressive approach, as described by Sundaresan and Weinstein, with wide resection, combination chemotherapy, and local radiotherapy demonstrated promising early results. Secondary spinal osteosarcoma caused by malignant transformation of pagetoid or previously irradiated bone is extremely aggressive and associated with early metastasis. A 5-year survival rate of 17% is reported in cases involving pagetoid bone, and the prognosis is even poorer in cases involving irradiated bone.
Ewing sarcoma is a malignant round cell tumor with a peak incidence in the second decade of life. The sarcoma was first described in 1921 by James Ewing, who called it an "endothelial myeloma." The neoplasm occurs twice as often in men as in women. Spinal involvement is seen in 3.5% of all Ewing sarcomas, and a large proportion of these arise in the sacrum.
Metastatic involvement of the spine is more common in the late stage of the disease. The vertebral body involvement seen on radiographs in patients with Ewing sarcoma can mimic the vertebra plana seen in patients with eosinophilic granuloma.
When the lesion is localized to the sacrum, the prognosis is worse because these particular lesions tend to be more aggressive and less responsive to chemotherapy and irradiation.
Chondrosarcoma is the third most common primary bone tumor behind myeloma and osteosarcoma. Although chondrosarcoma rarely affects the spine, it does so more often than osteosarcoma or Ewing sarcoma. The peak incidence of chondrosarcoma is in the fourth to sixth decade, with males affected four times more often than females. An estimated 6–10% of all chondrosarcomas arise in the spine.
Pain in the area of involvement is the first symptom. Fifty percent of patients have a palpable mass before being diagnosed. Approximately 4.5% have some form of neurologic deficit, varying from sensory deficits to frank paraplegia.
Radiographs show typical cortical destruction and paraspinal soft tissue calcification. MRI helps delineate the extent of soft-tissue and bony involvement.
Chondrosarcomas are radio resistant. Thus, the mainstay of treatment is wide excision. Survival is closely related to obtaining a clear surgical margin at the time of surgical excision. In the Mayo clinic series, 15 of 20 (75%) of the patients with chondrosarcoma died of local progression. Their 5-year survival rate was 21–55%, with a median survival of 6 years. High-dose irradiation therapy may have limited benefit for inoperable lesions.
A chordoma is a slow-growing tumor that arises from notochordal cells in the vertebral body. Physaliphorous cells, containing abundant vacuoles filled with glycogen and oxidative enzymes, are the distinctive cells of this neoplasm. Molecular analysis shows that chordoma cells express galectin-3, a carbohydrate binding protein that plays a role in cell differentiation, morphogenesis, and cancer biology. The neoplasm usually occurs in the fifth and sixth decades of life and afflicts men twice as often as women. Chordomas are found in the sacrum and coccyx in 55% of cases, in the basilar skull in 30%, and in the lumbar and cervical spine in 15%. The clinical course is indolent, and detection is often delayed until after metastasis occurs. Symptoms and signs include local pain, radiculopathy, and bowel or bladder dysfunction. Patients with cervicothoracic tumors can present with progressive dyspnea. Rectal examination can reveal a presacral mass.
After wide surgical resection, the local recurrence rate varies from 28–64%. Great care must be taken to prevent tumor spillage during resection because this can increase the local recurrence rate from 28% to 64%. Adjuvant radiation therapy is indicated when complete resection is not possible or when there is tumor spillage at the time of resection. Radiation therapy may allow an increased continuous disease-free survival. The 5-year survival rate in patients treated with irradiation alone is approximately 50%; that in patients treated with irradiation plus surgical resection is 71%. Virtually all patients eventually die from tumor recurrence.
METASTATIC DISEASE OF THE SPINE
Although the skeleton is the third most common site for metastatic disease, the spine, especially the thoracic spine, is the most frequently involved region of the skeleton. Approximately 70% of patients who die of cancer have evidence of vertebral metastasis on postmortem examination.
Lung, breast, prostate, renal, thyroid, and gastrointestinal carcinomas are all reported to metastasize to the spine, where lesions can lead to multilevel spinal instability and cord compression. Unfortunately, 30–50% of the bone must be destroyed before the metastatic involvement becomes evident on radiographs.
Many patients with spinal metastasis are asymptomatic. Symptoms, when they do occur, are typically a result of invasion of the tumor into the paravertebral soft tissues, compression of the spinal cord or nerve roots, or pathologic fracture and spinal instability. In these cases, patients frequently complain of severe, unrelenting back pain with or without neurologic sequelae. The pain typically wakes the patient up at night. The course may be rapid, leading to paraplegia or quadriplegia.
Technetium bone scanning reveals multiple sites of radioisotope uptake. MRI is the imaging study of choice to assess the extent of the tumor. Biopsy is necessary when the primary tumor is unknown and typically can be performed under CT guidance.
Most patients who do not develop progressive instability or neurologic compromise can be managed nonoperatively with systemic chemotherapy, local irradiation, and bracing.
Radiation therapy and chemotherapy protocols depend on the primary source of carcinoma. From 80% to 90% of patients suffering from spinal metastatic disease are reported to gain significant relief with radiation therapy. Irradiation can be started as early as 2 weeks after surgical decompression and fusion. Surgical intervention is warranted in patients who have severe pain and have failed to respond to conservative management. It is also indicated in patients who have significant neurologic dysfunction or spinal instability. Factors found to affect survival include preoperative neurologic status, anatomic site of primary carcinoma, and number of vertebral bodies involved. Patients with a slower onset of neurologic compromise have a better prognosis for recovery of neurologic function than patients with acute onset of neurologic compromise. Stabilizing constructs can consist of bone, metal, or methylmethacrylate (Figure 5–3).
Extradural tumors include hemangiomas, lipomas, meningiomas, and lymphomas. Surgical management usually involves laminectomy and tumor excision. This is often all that is needed for symptomatic relief in these slow-growing tumors.
Rheumatoid arthritis is the most common form of inflammatory arthritis. It affects 3% of women and 1% of men. The disease frequently affects the spine. The same inflammatory cells that destroy peripheral joints affect the synovium of apophyseal and uncovertebral joints, causing painful instability and neurologic compromise. Up to 71% of patients with rheumatoid arthritis show involvement of the cervical spine. The most common patterns of involvement are C1-C2 instability, basilar invagination, and subaxial subluxation. Sudden death associated with rheumatoid arthritis, most probably secondary to brain stem compression, is reported.
SYMPTOMS AND SIGNS
From 7% to 34% of patients present with neurologic problems. Documentation of neurologic function can be difficult because loss of joint mobility leads to general muscle weakness. Although many patients complain of nonspecific neck pain, atlantoaxial subluxation is the most common cause for pain in the upper neck, occiput, and forehead in patients with rheumatoid arthritis. Symptoms are aggravated by motion. Increasing compression of the spinal cord results in severe myelopathy with gait abnormalities, weakness, paresthesias, and loss of dexterity. Findings may also include Lhermitte sign (a tingling or electrical feeling that occurs in the arms, legs, or trunk when the neck is flexed), increased muscle tonus of the upper and lower extremities, and pathologic reflexes.
Instability of the upper cervical spine is determined on lateral flexion-extension radiographs. An atlantodens interval (ADI) that exceeds 3.5 mm is abnormal. Subluxation with an atlasdens interval of 10–12 mm indicates disruption of all supporting ligaments of the atlantoaxial complex (transverse and alar ligaments). The spinal cord in this position is compressed between the dens and the posterior arch of C1. Although the ADI is an important measurement for traumatic instability of the C1-C2 complex, the posterior atlantodens interval (PADI) is more prognostic to assess neurologic compromise. The PADI is a direct measure of the space available for the spinal cord at the C1-C2 level. The PADI is measured from the posterior aspect of the odontoid process to the nearest posterior structure (the foramen magnum or the posterior ring of the atlas). If the space available for the spinal cord is less than 13 mm, the likelihood that the patient will develop myelopathy is extremely high.
Cranial settling is present in from 5% to 32% of patients. The odontoid process should not project more than 3 mm above the Chamberlain line, which is a line between the hard palate and the posterior rim of the foramen magnum. The tip of the dens should not project more than 4.5 mm above the McGregor line, which is a line connecting the posterior margin of the hard palate to the occiput. The Clark classification divides the axis into thirds in the sagittal plane. In severe cases of cranial settling, the anterior arch of C1 moves from station 1 (the upper third of C2) to station 3 (the lower third of C2). Neurologic compromise occurs as a result of impingement of the dens into the brainstem and the upper cervical spinal cord. The vertebral arteries can also become occluded as they course between the dens and the foramen magnum to enter the skull.
Lateral subluxation and posterior atlantoaxial instability are less frequent. From 10% to 20% of patients with rheumatoid arthritis present with subaxial subluxation. Erosion of the facet joints and narrowing of the disks leads to subtle anterior subluxations often found on several levels. This results in the characteristic so-called stepladder deformity that occurs most commonly at the C2-C3 and C3-C4 levels.
Rheumatoid factor is positive in up to 80% of patients. The ESR rate is elevated and the hemoglobin is decreased in the active phase of the disease.
After plain radiographs, which should include lateral flexion-extension views, MRI is the study of choice to evaluate the degree of neural compression and deformity.
Indications for surgery are severe neck pain and increasing loss of neurologic function. Most commonly, a posterior arthrodesis between C1 and C2 is performed. A Gallie type or Brooks type of fusion can be done, or posterior transarticular screw fixation can be used. The latter obviates the need for postoperative halo immobilization. In cases of basilar invagination (cranial settling), extension of the fusion to the occiput is necessary. Preoperative halo traction is often required to reduce the subluxation or pull the odontoid process out of the foramen magnum. Often a suboccipital craniectomy is necessary to decompress the brainstem adequately. Good fixation can be obtained through the use of plate-screw and rod-screw constructs.
Ankylosing spondylitis is a chronic seronegative inflammatory disease that affects the axial skeleton, especially the sacroiliac joints, hip joints, and spine. Extraskeletal involvement is found in the aorta, lung, and uvea. The incidence of ankylosing spondylitis is 0.5–1 per 1000 people. Although males are affected more frequently than females, mild courses of ankylosing spondylitis are more common in the latter. The disease usually has its onset during early adulthood. However, juvenile ankylosing spondylitis affects adolescents (younger than 16 years) and has a predisposition toward hip involvement. The HLA-B27 surface antigen is found in 88%–96% of patients, and investigators postulate that an endogenic component (ie, HLA-B27) and an exogenic component (eg, Klebsiella or Chlamydia) are responsible for triggering of the disease process. The ESR is elevated in up to 80% of the cases but does not accurately reflect disease activity. The serum creatine phosphokinase (CPK), however, is a good indicator of the severity of the disease process.
SYMPTOMS AND SIGNS
The onset is insidious, with early symptoms including pain in the buttocks, heels, and lower back. Patients complain typically of morning stiffness, the improvement of symptoms with activity during the day, and the return of symptoms in the evening. The earliest changes involve the sacroiliac joints and then extend upward into the spine. Spinal disease results in loss of motion and subsequent loss of lordosis in the cervical and lumbar spine. Synovitis in the early stages leads to progressive fibrosis and ankylosis of the joints during the reparative phase. Enthesitis occurs at the insertion of the annulus fibrosus on the vertebral body with eventual calcification that results in the characteristic "bamboo spine." The pain from the inflammatory process subsides after full ankylosis of the affected joints occurs. Approximately 30% of patients develop uveitis, and 30% have chest tightness. Limited chest expansion indicates thoracic involvement. Fewer than 5% of patients have involvement of the aorta, characterized by dilation and possible conduction defects. In addition, patients may suffer from renal amyloidosis and pulmonary fibrosis.
The earliest radiographic changes are visible in the sacroiliac joints. Symmetric bilateral widening of the joint space is followed by subchondral erosions and ankylosis. Bony changes in the spine affect the vertebral body. Changes include loss of the anterior concavity of the vertebral body, squaring of the vertebra, and marginal syndesmophyte formation, which give the spine the appearance of bamboo. Ankylosis of the apophyseal joints also develops. The disease generally starts in the lumbar spine and migrates cephalad to the cervical spine. Atlantoaxial instability is seen occasionally.
The natural history of ankylosing spondylitis, with its slow progression over several decades, has to be considered in planning treatment. Initially, treatment consists of exercises and indomethacin. Approximately 10% of patients develop severe bony changes that eventually require surgical intervention. These changes characteristically include a fixed bony flexion deformity that limits their ambulatory potential. Hip disease should be addressed before correction of spinal deformities because correction of hip flexion deformities may allow significant compensation of the spinal kyphosis to allow adequate horizontal gaze.
Loss of lumbar lordosis can be treated by multilevel V-shaped osteotomies posteriorly (the Smith-Petersen procedure), by a decancellation procedure (the Heinig procedure) of L3 or L4, or by pedicle subtraction osteotomy based at L3 or L4. (Figure 5–4).
The spine is then fused in the corrected position. Utilization of modern fixation systems such as a pedicle screw system allows for early mobilization of the patient. Thorough preoperative assessment of the deformity and measuring of the chin-eyebrow-to-floor angle are helpful for the exact planning of the corrective osteotomy. Relative contraindications to surgery are poor general health and significant scarring of the major vessels, which may be injured when the spine is extended.
The cervical osteotomy is performed between C7 and T1. This approach avoids injury to the vertebral artery that usually enters the transverse foramen of C6. Although the procedure is usually performed under local anesthesia, the evolution of somatosensory and motor evoked potential monitoring of the spinal cord permits the use of general anesthesia. After removal of the posterior elements and neural decompression, the kyphotic deformity is corrected with gentle extension of the head. The head is held in the corrected position using internal fixation with plate-screw constructs or plate-rod constructs with adjunctive halo-vest immobilization.
DISEASES & DISORDERS OF THE CERVICAL SPINE
Principles of Diagnosis
In evaluating the cervical spine, the use of appropriate imaging studies is critical to a timely and precise diagnosis. Available imaging techniques include plain radiography, tomography, myelography, CT, CT with myelography, three-dimensional reconstruction CT, MRI, and scintigraphy. An understanding of the advantages and disadvantages of each technique is necessary for the proper selection of imaging studies and interpretation of results.
In evaluating the patient with neck pain, cervical spine radiographs are important in the initial search for a possible lesion. In the trauma setting, when a head or neck injury is suspected, radiographic studies must be carried out appropriately or a life-threatening lesion may be overlooked. The trauma series includes anteroposterior (AP), right oblique, left oblique, and open-mouth (odontoid) views in addition to an initial cross-table lateral view. When all five views are taken, sensitivity is 92%. Cervical spine precautions must be implemented throughout the radiographic evaluation (see Injuries of the Cervical Spine later in the chapter). In the absence of a history of trauma, the oblique and odontoid views are not always required.
The lateral view reveals the majority of traumatic lesions if performed correctly. Inadequate views can miss more than 20% of cervical spine injuries, however. All seven vertebrae should be clearly visible. Gentle traction on the upper extremities may be necessary to view C7. If this is unsuccessful, a swimmer's view may be necessary. Careful scrutiny of the prevertebral soft tissue, the anterior border of the vertebral bodies, the vertebral bodies themselves, the posterior border of the bodies, the spinal canal proper, and the posterior elements must be done.
The prevertebral region may reveal swelling consistent with a hematoma, and this may serve as the only clue to a traumatic lesion. The upper limits for the prevertebral space are 10 mm at C1; 5 mm at C2; 7 mm at C3 and C4; and 20 mm at C5, C6, and C7. The contours of the cervical bony structures are regular, and subtle incongruities may indicate significant instability. Variations in normal cervical anatomy do exist, however, and a familiarity with them may prevent an overzealous workup. The ADI normally measures less than 3 mm in adults and less than 4 mm in children.
In reviewing the AP radiograph, careful assessment of the interspinous distance must be undertaken. Vertical widening at a given level greater than 1.5 times the level above and below indicates a hyperflexion injury with posterior instability or interlocking of the posterior facets. Traumatic tilting may also be noted in the AP plane while not appreciated on the lateral view.
Oblique views taken at 45 degrees allow visualization of the articulations of the facet joints. The open-mouth view permits evaluation of the odontoid process, the lateral masses, and the articulations of the lateral masses, and it also permits assessment of the distance between each lateral mass and the odontoid process. In atlantoaxial rotatory subluxation, the lateral mass of the atlas that is rotated forward is closer to the midline (medial offset); the opposite mass is farther away from the midline (lateral offset). Burst fractures of the C1 ring cause overhang of the C1 lateral masses on C2. A combined overhang exceeding 6.9 mm is highly correlated with insufficiency of the transverse ligament and C1-C2 sagittal instability.
This radiographic series is equally important in evaluating infants and children with suspected congenital or developmental defects and adults with insidious neck pain. Arthritic changes may be subtle or readily apparent with osteophytes, disk space narrowing, and facet sclerosis. Bone quality can also be assessed on plain radiographs.
CT scans allow excellent visualization of the bony architecture and the paravertebral soft tissues of the cervical spine. The pedicles, laminae, spinous processes, and bony spinal canal can be examined with significantly better resolution when CT is used than when conventional radiographs are taken. CT with myelography or intrathecal contrast enhancement permits a visualization of the spinal canal contents.
CT is an appropriate modality for evaluating congenital variations and malformations, including spinal canal stenosis and spina bifida. Pars defects, atlantoaxial joint diseases, inflammatory changes, primary tumors, and metastatic carcinoma are well appreciated with CT. Although cervical disk disease is detectable when thin cuts and contrast enhancement are used with CT, it is better visualized with MRI.
In the trauma patient with questionable findings on plain radiographs, CT is integral in evaluating possible fractures or instability. Atrophy, deformity, and displacement of the spinal cord from acute or chronic injury are all appreciable with the use of intrathecal contrast. With the advent of MRI, however, CT is now reserved for the assessment of the bony architecture, which it does better than MRI.
Three-dimensional reconstruction of CT images gained wide clinical acceptance with the advancement of computer graphics. The reconstructions can be rotated in space to evaluate the anatomy from almost any perspective. This technique is valuable in the understanding of atlantoaxial rotatory subluxations or complex fractures of the spinal column.
MAGNETIC RESONANCE IMAGING
MRI permits axial, sagittal, coronal, or oblique plane analysis of the anatomy. It is routinely noninvasive, requiring contrast material in only selected cases.
MRI is the standard for assessing cervical spinal cord damage. Spinal cord tumors and trauma as well as central disk herniation can be easily visualized. In the preoperative evaluation of patients with spondylosis or disk herniation, MRI is the neuroimaging test of choice.
Intravenous paramagnetic agent gadolinium is commonly used to differentiate tissues receiving higher blood flow. This is helpful in the diagnosis of infection, tumor, and postsurgical scar.
Bone scans that employ technetium-99m phosphate permit assessment of physiologic processes within the musculoskeletal system. Metabolic, metastatic, and inflammatory abnormalities can be detected. Technetium-99m phosphate is incorporated into the hydroxyapatite in bone and reflects increased bone osteogenesis in a given region of bone. Early-phase imaging with technetium-99m gives blood flow information. Accordingly, subtle fractures, avascular necrosis, and osteomyelitis can be detected. Other radioisotopes used in scintigraphy include gallium-67 citrate, which labels serum proteins, and indium-111, which labels white blood cells. These labeling techniques are helpful in discerning areas of neoplasia or acute infection.
The atlantooccipital region is a frequent location for abnormalities. Various combinations involving bone and nervous structures are possible. During embryologic development, 42 somites are formed from the paraxial mesoderm. The somites divide into sclerotomes, which form the vertebral bodies after separation into a caudal and cephalad portion. The middle portion builds the intervertebral disk. The second, third, and fourth somites fuse and become the occiput and posterior part of the foramen magnum. The fate of the first somite is unclear. The development of the neural tube progresses simultaneously with that of the cartilaginous skeleton.
Disturbances of embryologic development can result in incomplete development or absence of a tissue or part, as found in dysraphism, aplasia of the odontoid process, incomplete closure of the atlas, or absence of the atlas facet. Lack of segmentation results in atlantooccipital fusion, block vertebrae, and possible instability at adjacent cervical levels. A disturbance of neurologic development, alone or in combination with bony defects, can lead to basilar impression, Arnold-Chiari malformation, and syringomyelia, all of which manifest in myelopathy.
Os odontoideum is an uncommon type of pseudarthrosis between the odontoid process and the body of the axis. It can cause significant atlantoaxial instability and myelopathy and can result in sudden death. The development of cervical myelopathy is thought to be a function of the amount of space available for the spinal cord. Because of the instability between C1 and C2, the spinal cord can become compressed against the anterior portion of the axis or the posterior ring of the atlas. In some cases, extrinsic compression of the vertebral arteries results in ischemic insult to the brain.
SYMPTOMS AND SIGNS
Patients with os odontoideum may be asymptomatic or may present with symptoms and signs that relate to atlantoaxial instability, such as ill-defined neck complaints or focal or diffuse neurologic deficits. A careful history may be needed to rule out trauma, although congenital os odontoideum may come to the attention of the surgeon secondary to a reported but inconsequential neck injury.
The radiographic findings may be extremely subtle and difficult to distinguish. In the mature skeleton, os odontoideum appears as a radiographic lucency. In children younger than 5 years, however, an anomalous gap may be confused with a normal neural synchondrosis. Flexion-extension views must therefore be obtained to demonstrate motion between the odontoid process and the body of the axis. The ossicle in os odontoideum is either round or ovoid, with a smooth surface and uniform cortical thickness. It is usually approximately half the size of the normal odontoid process. In traumatic nonunion, the edge is irregular with a narrow gap. The fracture line may involve the body of C2 as well. An additional radiologic finding in os odontoideum is hypertrophy of the anterior ring of the atlas with a corresponding hypoplastic posterior ring. In flexion-extension views, the ossicle travels with the anterior ring of the atlas (Figure 5–5). In cases that are difficult to diagnose, further studies include open-mouth views, tomograms, and CT reconstructions.
Patients diagnosed with os odontoideum must be warned of the gravity of the situation because minimal trauma can be fatal. Patients with cervical myelopathy can be treated with traction, immobilization, or both, but they often require subsequent posterior fusion. Sometimes symptoms are reversible with or without intervention. Management of asymptomatic patients with instability is controversial. The benefits of surgical stabilization in an attempt to avoid potentially lethal injury from relatively minor trauma are counterbalanced by the possible complications of surgery.
If fusion is indicated, usually a posterior fusion of C1-C2 is adequate. Different fusion techniques are available. Most surgeons use the Gallie technique or the Brooks technique. The Gallie technique involves the use of a single block-shaped bone graft between the posterior ring of C1 and the spinous process of C2. A single sublaminar wire holds the graft in place. The Brooks technique uses from two to four sublaminar wires, and two bone grafts are wedged between the laminae of C1 and C2. The loss of motion between atlas and axis results in an overall decrease of 50% of cervical rotation. Use of transarticular screws or screw-rod constructs that purchase into the lateral masses of C1 and the pedicle of C2 are rigid enough to allow the patient to mobilize without a halo vest.
Klippel-Feil syndrome refers to an array of clinical disorders associated with congenital fusion of one or more cervical vertebrae. The fusion, which may be multilevel, results from a failure of the normal division of the cervical somites during the third through eighth weeks of embryogenesis. The cause of this failure is unknown. The syndrome was first described in 1912 by M. Klippel and A. Feil as a triad of clinical features: a short "web" neck, a low posterior hair line, and limited cervical neck motion. Interestingly, only 50% of patients with the syndrome that now bears the names of Klippel and Feil present with this classic triad.
Various conditions were subsequently seen in association with congenitally fused cervical vertebrae. These include scoliosis (seen in approximately 60% of cases), renal abnormalities (in 35%), deafness (in 30%), Sprengel deformity (in 30%), synkinesis or mirror movement (in 20%), congenital heart defects (in 14%), brainstem anomalies, congenital cervical stenosis, adrenal aplasia, ptosis, Duane contracture, lateral rectus palsy, facial nerve palsy, syndactyly, and upper extremity diffuse or focal hypoplasia.
SYMPTOMS AND SIGNS
Decreased range of motion is the most frequent finding in patients with cervical spine involvement. Involvement of only the lower cervical spine or fusion of fewer than three vertebrae results in minimal loss of motion, however. Patients may also be able to compensate at other cervical interspaces, masking any loss of motion.
Neck shortening is difficult to detect unless extreme. Webbing of the neck (pterygium colli), facial asymmetry, or torticollis is seen in fewer than 20% of patients. Webbing of the neck can nevertheless be dramatic, with underlying muscle involvement extending from the mastoid to the acromion. Sprengel deformity, which results from a failure of either or both scapulae to descend from their embryologic origin at C4, is seen in approximately 30% of patients. Sometimes an omovertebral bone bridges the cervical spine to the scapulae and limits the neck and shoulder motion.
Cervical spine symptoms in Klippel-Feil syndrome are related to the secondary hypermobility of the unfused vertebrae. Except for atlantoaxial joint involvement, resulting in a significant decrease in occipital rotation, the fused joints at a given level are asymptomatic. Because of the increased mechanical demands placed on the uninvolved joints, secondary osteoarthritis, disk degeneration, spinal stenosis, and instability may result at these levels. Neurologic sequelae, usually confined to the head, neck, and upper extremities, result from impingement of the cervical nerve roots. With progressive cervical instability, the spinal cord may become involved, leading to spasticity, weakness, hyperreflexia, and even quadriplegia or sudden death from minor trauma.
Radiographic findings (Figure 5–6) of congenital cervical vertebral fusion are diagnostic of Klippel-Feil syndrome. This may present as synostosis of two vertebral bodies or as a multilevel fusion, as originally described in 1912. Other noteworthy findings are flattening of the involved vertebral bodies and the absence of disk spaces. Hypoplastic cervical disks in a child are often hard to appreciate radiographically. If suspected, flexion-extension views can be taken. CT scanning and MRI have improved the assessment of bony and nerve root involvement.
Spinal canal stenosis is not usually seen until adulthood. Although anterior spina bifida is infrequent, the posterior form is not. Enlargement of the foramen magnum with fixed hyperextension often accompanies the cervical spina bifida. Hemivertebrae are also noted.
Involvement of the upper thoracic spine can occur and may be the first sign of an undiagnosed cervical synostosis.
Because of the potential for multiorgan involvement in patients with Klippel-Feil syndrome, an electrocardiogram and renal ultrasound are also recommended.
Treatment of the cervical spine abnormalities is limited. Multilevel involvement leads to hypermobility at uninvolved joints, so affected patients should be cautious in their activities. Prophylactic surgical stabilization is not routinely performed in asymptomatic patients because the risk-benefit ratio has not been well defined. In some cases, however, surgical fusion is performed.
Secondary osteoarthritis may be treated in the usual manner, including use of a cervical collar, traction, and antiinflammatory agents. Nerve root impingement requires careful evaluation before surgical decompression because more than one level may be involved and there may also be central abnormalities.
Surgical correction of the aesthetic deformities is only moderately successful. Carefully selected candidates may benefit from soft tissue Z-plasty or tenotomies. This may improve the appearance of the patient but does not affect cervical motion.
Children with mild involvement can be expected to grow up to lead healthy, normal lives. Patients with more severe involvement can do comparably well if the associated conditions are successfully treated at an early age.
Cervical spondylosis is defined as a generalized disease process affecting the entire cervical spine and related to chronic disk degeneration. In approximately 90% of men older than 50 years and 90% of women older than 60 years, degeneration of the cervical spine can be demonstrated by radiographs. Initial disk changes are followed by facet arthropathy, osteophyte formation, and ligamentous instability. Myelopathy, radiculopathy, or both may be seen secondarily. Cervical myelopathy is the most common form of spinal cord dysfunction in people older than 55 years. People older than 60 years are more likely to have multisegmental disease. The incidence of cervical myelopathy is twice as great in men as in women.
The relationship between the spinal cord and its bony arcade has been studied extensively. The first publication on the subject was written in the early 1800s and gave the first account of a "spondylotic bar," which was actually a thickened posterior longitudinal ligament protruding into the canal secondary to disk degeneration. Subsequent work revealed that disk degeneration and osteoarthritis could lead to spinal cord and nerve root impingement.
Acute traumatic disk herniation was distinguished from the chronic spondylotic process in the mid-1950s. Concurrently, anterior spinal artery impingement by the disk or osteophyte was proposed as part of the pathogenesis. As indicated in these studies, disk degeneration starts with tears in the posterolateral region of the annulus. The subsequent loss of water content and proteoglycans in the nucleus then leads to a decrease of disk height. The longitudinal ligaments degenerate and form bony spurs at their insertion into the vertebral body. These so-called hard disks have to be distinguished from soft disks, which represent acute herniation of disk material into the spinal canal or into the neural foramen. The most frequently involved levels are the more mobile segments: C5-C6, C6-C7, and C4-C5. The converging of the cervical disk space may result in buckling of the ligamentum flavum, with further narrowing of the spinal canal. Segmental instability results in hypertrophic formation of osteophytes by the uncovertebral joint of Luschka and by the facet joints. These prominent spurs result in compression of both the exiting nerve roots and the spinal cord.
Further work revealed that the sagittal cervical canal diameter was appreciably smaller (3 mm on average) in the myelopathic spondylotic spine than in the normal spine. The anterior-posterior dimensions of the cervical spinal canal measure between 17 and 18 mm in normal individuals. Spinal canal stenosis is present when the canal diameter becomes less than 13 mm. With extension of the neck, both the spinal canal diameter and the neuroforaminal diameter decrease.
SYMPTOMS AND SIGNS
Headache may be the presenting symptom of cervical spondylosis. Usually, the headache is worse in the morning and improves throughout the day. It is commonly located in the occipital region and radiates toward the frontal area. Infrequently, patients complain of a painful, stiff neck. Signs include decreased range of motion, crepitus, or both. With more advanced cases, radicular or myelopathic symptoms may be present.
Cervical Spondylotic Radiculopathy
Cervical radiculopathy in spondylosis can be quite complex, with nerve root involvement seen at one or more levels and occurring either unilaterally or bilaterally. The onset may be acute, subacute, or chronic, and impingement on the nerve roots may be from either osteophytes or disk herniation. With radiculopathy, sensory involvement in the form of paresthesias or hyperesthesia is more common than motor or reflex changes. Several dermatomal levels may be involved, with radiation into the anterior chest and back. The chief complaint is radiation of pain into the interscapular area and into the arm. Typically, patients have proximal arm pain and distal paresthesias.
Cervical Spondylotic Myelopathy
Cervical myelopathy has a variable clinical presentation, given the complex pathogenic mechanisms involved. These include static or dynamic canal impingement, facet arthropathy, vascular ischemia, and the presence of spondylotic transverse bars. In addition, given its neuronal topography, the cord may be affected in dramatically different ways by relatively minor differences in anatomic regions of compression. The clinical course of myelopathy is usually progressive, leading to complete disability over a period of months to years with stepwise deteriorations in function.
Patients often present with paresthesias, dyskinesias, or weakness of the hand, the entire upper extremity, or the lower extremity. Deep aching pain of the extremity, broad-based gait, loss of balance, loss of hand dexterity, and general muscle wasting are found in patients with advanced myelopathy. Impotence is not uncommon in these patients.
Hyperextension injuries of the spondylotic cervical spine can precipitate a central cord syndrome in which motor and sensory involvement is typically greater in the upper extremities than the lower extremities. Recovery from this injury is usually incomplete. Complete quadriplegia can also occur if the preexisting stenosis is severe. In this setting, the 1-year mortality approaches 80%.
Deep tendon reflexes can be either hyporeflexic or hyperreflexic, with the former seen in anterior horn cell (upper extremity) involvement and the latter seen in corticospinal tract (lower extremity) involvement. Hyporeflexia is found at the level of compression; hyperreflexia occurs on the level below. Long-tract signs, such as the presence of the Hoffmann reflex or Babinski reflex, indicate an upper motor neuron lesion. Clonus is often present though asymmetric. Upper extremity involvement is often unilateral, whereas lower extremities are affected bilaterally. High cervical spondylosis (C3-C5) leads to complaints of numb and clumsy hands; myelopathy of the lower cervical spine (C5-C8) presents with spasticity and loss of proprioception in the legs.
Abdominal reflexes are usually intact, enabling the clinician to differentiate spondylosis from amyotrophic lateral sclerosis, in which reflexes are often absent. Multiple compressions of the spinal cord cause more severe deterioration functionally and electrophysiologically than a single-level compression does.
Although spondylosis results from cervical spine degeneration, not every patient with radiographic evidence of cervical disk degeneration has symptoms. Furthermore, patients with all the radiographic stigmas of cervical spondylosis may be asymptomatic, and others with clinical evidence of myelopathy may show only modest radiographic changes. This paradox is explainable by canal size differences, with the smaller-diameter canal having less space to buffer the degenerative lesion.
The average AP diameter of the spinal canal measures 17 mm from C3 to C7. The space required by the spinal cord averages 10 mm. The dural diameter increases by 2–3 mm in extension. The smallest sagittal anteroposterior diameter is measured between an osteophyte on the inferior aspect of the vertebral body to the base of the spinous process of the next vertebra below. An absolute spinal canal stenosis exists with a sagittal diameter of less than 10 mm. The stenosis is relative if the diameter measures 10–13 mm.
Plain film findings also vary according to the stage of spondylosis at which they were taken. Radiographs may appear normal in early disk disease. Alternatively, they may show single or multilevel disk space narrowing with or without osteophytes. C5-C6 and C6-C7 are the two most commonly involved segments (Figure 5–7). Vertebral body sclerosis at the adjacent base plates may also be seen. Cortical erosion is uncommon and indicates an inflammatory process such as rheumatoid arthritis.
Oblique views permit evaluation of the facet joints and detection of osteophytosis and sclerosis. The superior facets undergo degeneration more frequently than their inferior counterparts. The superior joints may then subluxate posteriorly and erode into the lamina below. Inferior osteophytes, however, may prevent significant slippage. If instability seen on flexion-extension views is significant (greater than 3.5 mm when measured at the posteroinferior corner of the vertebral body), foraminal stenosis as well as vertebral artery impingement may result.
MRI permits visualization of the entire cervical canal and spinal cord by showing the spinal cord and nerve roots in two planes. The use of a contrast-enhanced CT scan is occasionally required in elderly (more than 60 years) patients with advanced degenerative bony changes of the cervical spine. Accurate identification of the location and extent of pathologic changes is necessary to determine the optimal approach for decompression. Selective nerve root blocks and electromyography may be useful to identify the level of involvement.
Inflammatory, neoplastic, and infectious conditions can mimic cervical spondylotic radiculopathy and myelopathy.
The cervical spine is affected in most rheumatoid arthritis patients. Atlantoaxial subluxation or subaxial instability can cause symptoms similar to those seen in degenerative cervical myelopathy. A primary tumor or metastatic disease can present with unremitting neck pain, often more intense at night. MRI can distinguish neoplastic conditions from degenerative disorders. Infections of the cervical spine occur in children and in elderly (more than 60 years) or immunocompromised individuals. Multiple sclerosis should be considered in the differential diagnosis. It occurs in younger patients but can present with similar motor signs. Pancoast tumors may invade the brachial plexus, resulting in upper extremity symptoms. Syringomyelia presents with tingling sensations plus motor weakness. A low protein concentration in the cerebrospinal fluid and characteristic changes on MRI are found. Disorders of the shoulder, especially rotator cuff tendinitis, can imitate cervical radiculopathy. Compressive peripheral neuropathies, such as thoracic outlet syndrome, also have to be ruled out.
Patients should be divided into three groups, according to the predominance of their symptoms: neck pain alone, radiculopathy, and myelopathy. The duration and progression of symptoms need to be considered in the planning of treatment. Several studies suggest that patients with cervical radiculopathy or myelopathy have better long-term results from surgery if symptoms are of short duration.
Initial management of patients with cervical spondylosis may involve a soft collar, antiinflammatory agents, and physical therapy consisting of mild traction and the use of isometric strengthening and range-of-motion exercises. The soft cervical collar should be worn only briefly, until the acute symptoms subside. Analgesics are important in the acute phase, and muscle relaxants are helpful in breaking the cycle of muscle spasm and pain. Diazepam should be avoided because of its side effects as a clinical depressant. Epidural corticosteroid injections may be efficacious in patients with radicular pain. Trigger point injections are an empirical form of therapy that seems to work well in patients with chronic neck pain.
The value of cervical traction remains unclear. It is contraindicated in patients with cord compression, rheumatoid arthritis, infection, or osteoporosis. A careful screening of roentgenograms before treatment is mandatory. No evidence indicates that home traction is more effective than manual traction. Isometric strengthening exercises of the paravertebral musculature should be started after the acute symptoms resolve. The patient should be instructed to start a home exercise program early, to avoid long-term dependency on passive therapy modalities. Although ice, moist heat, ultrasound, and transcutaneous electrical nerve stimulation (TENS) are safe to use, there is no scientific proof of their efficacy.
Surgical intervention should be considered if the patient does not respond to a conservative treatment protocol or shows evidence of deteriorating myelopathy or radiculopathy. The spinal cord can be effectively decompressed by either anterior, posterior, or combined approaches.
The anterior approach allows multilevel diskectomy, vertebrectomy, foraminotomy, and fusion with tricortical iliac crest bone grafts or strut grafts. Newer instrumentation techniques, such as cervical plates (Figure 5–8), alleviate the need for halo immobilization. However supplemental posterior fixation and fusion should be added if more than three vertebral levels are decompressed anteriorly. Posterior fixation minimizes the risk of anterior dislodgement of the graft even in the presence of solid anterior fixation. Anterior interbody fusion after decompression for a herniated cervical disk (Figure 5–9) has a high success rate.
Cervical disk replacement prostheses were also developed to provide a motion-sparing alternative to anterior cervical diskectomy and fusion. By maintaining existing motion or restoring motion to a diseased motion segment, these prostheses have the potential to decrease the rate of symptomatic adjacent segment degeneration. Currently, clinical trials approved by the Food and Drug Administration (FDA) are under way to assess the efficacy of these devices against the outcomes that can be obtained with anterior cervical diskectomy and fusion.
The number of involved levels may be important in deciding which of the surgical approaches to use. Patients with cervical myelopathy and involvement of more than three vertebral body levels may be best managed by a posterior approach. Multilevel laminectomy or laminoplasty shows excellent results. If laminectomies are performed, the facet joints and capsules should be preserved to minimize the chance of postlaminectomy deformity. Late swan-neck deformities after laminectomy can be avoided with simultaneous posterior fusion using lateral mass plates. Laminoplasty is advantageous in that the cervical spinal cord can be decompressed without the high risk of developing late deformity. In addition, the morbidity associated with instrumentation and fusion can be avoided.
Operative treatment in cases of cervical spondylotic radiculopathy and myelopathy must be individualized for every patient.
Cervical spondylosis is generally a progressive, chronic disease process. In a study of 205 patients with neck pain, Gore et al. found that many patients had decreased pain at the 10-year follow-up, but those with the most severe involvement did not improve. Conservative measures may retard the disease process in its early stages. If myelopathy or radiculopathy becomes clinically evident, surgical intervention is often necessary. For disease involving less than three vertebral levels, early anterior decompression and fusion improves the clinical outcome, particularly in the elderly (more than 60 years) individual who suffers from cervical myelopathy.
OSSIFICATION OF THE POSTERIOR LONGITUDINAL LIGAMENT
Ossification of the posterior longitudinal ligament (OPLL) is a relatively common cause of spinal canal stenosis and myelopathy in the Asian population. Its overall incidence is 2–3% in Japan, compared with 0.6% in Hawaii and 1.7% in Italy. Males are affected more often than females, and the peak age at onset of symptoms is the sixth decade. Although the cause of the disorder is unknown, it may be controlled by autosomal dominant inheritance because it is found in 26% of the parents and 29% of the siblings of affected patients. The disorder is associated with several rheumatic conditions, including diffuse idiopathic skeletal hyperostosis (DISH), spondylosis, and ankylosing spondylitis.
Almost all patients have only mild subjective complaints at the onset, although 10–15% of them complain of clumsiness and spastic gait. Nevertheless, minor trauma can lead to acute deterioration of symptoms and can result in quadriplegia. Spastic quadriparesis is the most common neurologic presentation.
Ossification of the posterior longitudinal ligament can easily be diagnosed on plain lateral radiographs. The levels most frequently involved are C4, C5, and C6. A segmental type of disorder is distinguished from the continuous, local, and mixed type on the basis of the distribution of lesions behind the vertebral bodies. CT scanning is helpful in assessing the thickness, lateral extension, and AP diameter of the ossified ligament. More than 95% of the ossification is localized in the cervical spine, although extension into the thoracic spine is reported to be a cause of persistent myelopathy following cervical decompression.
Enchondral ossification is mainly responsible for the formation of the ossified mass, which connects to the upper and lower margins of the vertebral bodies. In many cases, the ossified material is closely adherent to the underlying dura and makes excision quite hazardous. Compression of the spinal cord results in atrophy and necrosis in the gray matter and demyelinization of the white substance.
Neurologic improvement with either conservative or surgical treatment is achieved in a significant proportion of patients. The patients with severe myelopathy require neural decompression by an anterior, posterior, or combined approach. Sophisticated posterior decompression techniques, such as the open-door laminoplasty, have yielded excellent long-term results for OPLL lesions that do not comprise more than 50% of the spinal canal cross-sectional area.
LOW BACK PAIN
Low back pain is a very common symptom in the general population. According to the Quebec Task Force on Spinal Disorders, more than 80% of the population experience some low back pain at some point in their life. The overall prevalence of low back pain in the United States is estimated to be approximately 18%. The annual incidence of low back pain is 15–20%. Males are affected as often as females, and the pain is usually self-limiting, with 50% of affected patients recovering by 2 weeks and 90% recovering by 6 weeks. Only 1% of the population in the United States is chronically disabled by back symptoms. If a patient stays off work for more than 2 years because of problems of the lower back, he or she is unlikely to return to work at all.
The socioeconomic impact of back problems is enormous. Over 14% of all new patient visits to physicians are for complaints of low back pain, and it is the most common reason for visits to the orthopedic surgeon. Costs are estimated to range from $20 billion to $50 billion annually, with 10% of the patients accounting for 85–90% of the costs. Investigators showed that patients with chronic low back pain tend to be dissatisfied with their vocation, viewing it as boring and repetitious. They also have an increased divorce rate, more problems with headaches and gastrointestinal ulcers, and a higher rate of alcoholism than the average population. The extensive use of the Minnesota Multiphasic Personality Inventory (MMPI) in the assessment of patients with chronic low back pain demonstrates an association among chronic pain, somatization, and hypochondriasis.
Etiology & Pathophysiology
The exact cause of symptoms is found in only 12–15% of patients. A thorough understanding of the lumbar anatomy and its function is important because lower back pain may originate from the disk, vertebral body, or posterior elements or may be unrelated to the spine. The earlier concept of a motor segment is now superseded by the concept of a functional spinal unit (FSU), or motion segment. The FSU consists of two adjacent vertebrae and the intervertebral disk. It forms a three-joint complex with the disk in front and two facet joints posteriorly. The motion segment involves joint capsules, ligaments, muscles, nerves, and vessels as well. Changes in one joint affect the other two. Disk degeneration leads to disk space narrowing, endplate sclerosis, abnormal stress on facet joints, and, ultimately, facet degeneration.
Significant emphasis is newly placed on the idea of the intervertebral disk as a pain generator. These axial pain syndromes of diskogenic origin are roughly categorized as internal disk disruption, degenerative disk disease, and disk degeneration as a sequela of segmental instability. The overriding principle is that the posterior portion of the annulus fibrosus is innervated by fibers of the sinuvertebral nerve that is a branch of the dorsal root ganglion. Irritation of the sinuvertebral nerve is thought to be responsible for axial back pain. In the rat, Suseki showed that these pain fibers are not innervated segmentally. Sensory information from the lumbar intervertebral disks is conducted to other spinal levels via the paravertebral sympathetic trunks. These data suggest that decompression of the nerve root at one level is unlikely to help with low back pain symptoms.
Principles of Diagnosis
HISTORY AND PHYSICAL EXAMINATION
A focused history and physical examination of the patient are crucial for the appropriate diagnosis and treatment. Typical initial questions include the following: What is the problem? Which areas are affected? How much does the pain interfere with sitting, standing, and walking? Were there previous episodes? If so, how long did they last? Are there bowel or bladder symptoms? The presence of bowel or bladder symptoms may indicate a cauda equina syndrome. Leg and buttock pain are usually indicative of nerve root irritation from a herniated disk or neuroforaminal stenosis, whereas axial low back pain is often mechanical. Drawing a diagram of the areas affected by pain may be of help, and a history of other medical problems may provide additional clues.
The physical examination is subjective and requires the patient's interpretation and cooperation. The diagnostic significance of range-of-motion measurements of the spine is questionable. Although a positive result in the straight leg–raising test is highly suggestive of nerve root irritation in a young patient, use of this test is less reliable in an older (more than 50 years) patient. In addition to noting a general impression of the patient and testing for sensory and motor deficits, the clinician should check the patient's response to local touch, axial loading, and simulated rotation and should record the presence of other nonorganic signs (Waddell signs). Patients with chronic low back pain demonstrate illness behavior and score high in nonorganic signs.
The pain is considered acute if it lasts less than 6 weeks and chronic if it lasts longer than 12 weeks. The most common cause is a lumbar strain after a lifting or twisting event or without known trauma. Patients usually present with localized pain in the lumbosacral area, in some cases with pain radiating into the buttocks. Palpation of the paraspinal muscles reveals spasms, and motion is limited. Results of the neurologic examination are normal, and the straight leg–raising test is negative. Sensation and reflexes are symmetric.
Radiographs are not necessary during the initial evaluation. If a patient's symptoms do not resolve, radiographs may be obtained. They are indicated in patients who are older than 50 years and have a history of trauma, cancer, weight loss, pain at rest, drug abuse, neurologic deficit, or fever. Radiographs may appear normal or demonstrate disk space narrowing, osteophyte formation, or localized instability on lateral flexion-extension views. No association is established between low back pain and the presence of disk space narrowing, transitional vertebrae, Schmorl nodes, the disk vacuum sign, claw spurs, lumbar lordosis, or spina bifida occulta. Routine flexion-extension views of the lumbar spine are not indicated and rarely demonstrate obvious segmental instability.
If plain radiographs are unsuccessful in establishing the cause of the patient's problem and the patient does not respond to conservative therapy, additional imaging studies may be helpful.
MRI of the lumbar spine is noninvasive and excellent in assessing compromise of neural structures. For example, MRI with gadolinium enhances the imaging of intraspinal tissue and can help distinguish scar formation after previous surgery from new encroachment on neural structures by disk material. CT scanning, with and without enhancement by myelography, can be helpful if MRI studies are not possible or do not yield positive results. CT myelography is especially useful to assess patients who have had spinal instrumentation. If an infection of the spine is suspected, a gadolinium-enhanced MRI is an extremely sensitive and specific test for diskitis, spinal osteomyelitis, and epidural abscess.
Disk degeneration is common in adults with low back pain. Caution in interpreting the results of MRI and CT is necessary, however, because studies show that positive findings are seen in asymptomatic patients who undergo MRI or CT evaluation of the lumbar spine. When MRI was used to examine the lumbar spines of asymptomatic volunteers, disk herniation was found in 17% of those younger than 40 years, 22% of those between 40 and 59 years, and 36% of those older than 60 years. In the oldest group, 21% showed lumbar stenosis without symptoms. When CT was used to examine the lumbar spines of asymptomatic volunteers, disk herniation was found in 35.4% of the volunteers.
If disk degeneration is suspected to be the cause of lower back pain, a diskogram may be indicated. In this provocative test, dye is injected into the nucleus pulposus, and then a CT scan of the injected segment is taken. The pain response of the patient seems to be the most accurate indication that the injected disk might be responsible for the patient's pain. However, the use of provocative diskography in the evaluation of axial back pain continues to be controversial. The results are subjective and depend very much on the patient's psychological status at the time of the procedure. Diskography is more sensitive than MRI to assess internal disk disruption, although questions about the value of using diskography, facet blocks, and other invasive tests remain to be answered.
Principles of Treatment
Management of low back pain has to be tailored to the individual. The goal is early return to work. Most patients can simply modify their activities during the acute phase. If a serious pathologic condition is ruled out, a more aggressive approach is warranted because bed rest for more than 2 days has serious side effects: The body is in a catabolic state; 3% of muscle bulk is lost daily; 6% of bone is demineralized in 2 weeks; and restriction of social activities leads to illness behavior, depression, and loss of interest and motivation. Iatrogenic disability must be avoided. Patients with acute low back pain should avoid sitting and lifting. Mild analgesics and antiinflammatory agents are useful in the acute phase of the disease. Educational programs, aerobic endurance exercises, and abdominal conditioning also prove helpful.
No evidence indicates that the following treatment modalities are useful in the management of acute low back pain: TENS, interferential stimulation, traction, manipulation in the presence of radicular signs, acupuncture, biofeedback, narcotics for longer than 2 weeks, trigger point injections, and muscle relaxants.
Patients who have low back pain that persists for more than 3 months occasionally benefit from antidepressant medication. If narcotic analgesics are not needed and if surgery is ruled out, they may be candidates for a functional restoration program involving an interdisciplinary approach with physical therapists, occupational therapists, psychologists, and medical professionals. One study showed that 87% of program participants returned to work, whereas only 41% of control subjects did so.
A subgroup of patients who have persistent, disabling axial low back pain of diskogenic origin in the absence of other psychological or organic pathologies may benefit from complete diskectomy and interbody fusion. This can be performed through an anterior open or laparoscopic approach or via the posterior approach. Good to excellent outcomes are reported in up to 70–80% of patients.
Disk replacement surgery was first introduced in the early 1950s with variable results. As spinal fusion demonstrated itself to be a relatively efficacious procedure, spinal arthroplasty quickly lost its initial enthusiasm. However, as the limitations of spinal fusion became evident and technology improved to design better bearing surfaces, disk replacement is enjoying a resurgence in interest. The theoretical advantages, which include preserving or restoring motion after removal of the painful disk, preventing late adjacent segment degeneration, and improving function without the need for fusion, should be weighed against the possible complications. These include malpositioning of the prosthesis, extrusion of the device, failure of the polyethylene articulating surface, and osteolysis. Clinical outcomes of single-level lumbar total disk replacement are improved over single-level fusion in the first 6 months following surgery. However, the results are similar to fusion at 2-year follow-up. The SB-Charite III total disk replacement is the first device to be approved by the FDA for this application. Other comparable devices are currently under FDA-approved randomized, prospective clinical trials.
Other less invasive therapies for diskogenic axial back pain are also available. One of these, an intradiskal electrothermal therapy, attempts to thermally ablate the painful nerve fibers in the posterior annulus. The reported outcomes on this procedure are variable, and it is unclear whether the results are a significant improvement over the natural history of axial low back pain.
LUMBAR DISK HERNIATION
Symptomatic disk herniations are seen in all age groups but have their peak in patients between 35 and 45 years of age. Although smoking is a general risk factor for disk degeneration and herniation, occupational risk factors include sedentary work and motor vehicle driving. Sciatica, characterized by pain radiating down the leg in a dermatomal distribution, is the most common symptom and found in 40% of patients with disk herniation. Approximately 50% of patients recover within 1 month, and 96% function normally by 6 months. The rate of surgical treatment in the United States is three times higher than that in Sweden.
A disk herniation is usually preceded by degenerative changes inside the disk. Circumferential tears in the annulus progress to radial tears, and these in turn frequently cause internal disruption or frank herniation. Two pathologic patterns can be distinguished. In a contained disk protrusion, the annulus fibers are intact. In a noncontained disk herniation, the annulus is completely disrupted. Disk material can be subligamentous or sequestered as a free fragment. The pain accompanying disk herniation may be caused by direct pressure on the nerve root or may be induced by breakdown products from a degenerated nucleus pulposus or by an autoimmune reaction. Disk material is a direct source of chemically irritative substances such as phospholipase A2, prostaglandin E2, substance P, and lactic acid. Biochemical studies in operated disk fragments demonstrate an advanced aging process. The hydration of the disk changes from 90% during childhood to 70% by the sixth decade, and the ability of proteoglycans to aggregate decreases with advancing age.
SYMPTOMS AND SIGNS
The typical sciatica is commonly preceded by back pain for a period of days or weeks. This scenario suggests that a compression of nerve fibers in the outer layers of the annulus preceded the rupture of the disk material into the spinal canal and the advent of leg pain. A complete physical examination is necessary. Although the dominating symptom is pain, patients often present with scoliosis or a sciatic list. The mobility of the lumbar spine is diminished more in flexion than in extension. Coughing, sneezing, or a voluntary Valsalva maneuver commonly aggravates the radiating pain. Prolonged sitting also accentuates the pain.
In more than 90% of cases, lumbar disk herniations are localized at L4-L5 and L5-S1. Paracentral disk herniations typically affect the traversing nerve root at the affected level, whereas lateral and foraminal herniations affect the exiting nerve root at the affected level. Compression of the L4 nerve root, which leads to pain and numbness in the L4 dermatome, can occur in a central disk herniation at L3-L4 or in a lateral herniation at L4-L5. When the L4 nerve root is affected, there may be weakness of the quadriceps muscle, and the patella tendon reflex may be depressed or absent. Central or paracentral disk herniations at L4-L5 usually compromise the L5 nerve root, where they may cause numbness in the L5 dermatome and weakness of the foot and toe dorsiflexors. A disk herniation at L5-S1 usually compromises the S1 nerve root, causing numbness or pain in the S1 dermatome, weak plantarflexion of the foot, loss of the Achilles tendon reflex, or tingling in the nerve distribution.
The straight leg–raising test should be performed. The Lasègue sign (pain when the affected leg is elevated) is positive in 98% of patients with lumbar disk herniation, and the cross-Lasègue sign (pain radiating to the affected leg when the contralateral leg is elevated) is positive in 20%. This test is less accurate in older (more than 60 years) patients and in patients with chronic lumbar disk herniation. For lesions involving the L3 or L4 nerve root, the femoral nerve stretch test should be applied. The radicular pain is reproduced when the knee is flexed while the hip is slightly extended.
MRI is the study of choice for diagnosis of a herniated disk (Figure 5–10). Because 28% of asymptomatic patients show a disk herniation on MRI, it is important to correlate the level of spinal involvement with the peripheral nerve deficit. CT scanning and myelography are less frequently used to confirm the diagnosis.
Radicular pain is typical and should be distinguished from referred pain, which commonly radiates from the lower back into the posterior thigh and ends at the knee level. The posterior spinal elements are frequently a source of this pain. Anterior thigh pain may indicate a retroperitoneal process, such as renal disease or a tumor of the uterus or bladder. Hip disorders, including trochanteric bursitis and coxarthrosis, must be ruled out. The presence of incontinence, perianal numbness, and bilateral leg pain associated with numbness suggests a cauda equina syndrome and requires immediate surgical attention. A primary tumor or metastatic disease involving the spine can present with radiculopathy, and symptoms and signs such as pain at night, a previous history of cancer, and loss of weight should raise the suspicion of the examiner.
In cases of lumbar disk herniation, the goal of treatment is to return the patient to normal activities as quickly as possible. Unnecessary surgery should be avoided. In determining the proper treatment plan, a knowledge of the natural history of lumbar disk herniation is important. In a prospective study of 280 patients with lumbar disk herniations, Weber compared the outcome of a group treated conservatively with the outcome of a group treated with diskectomy. Although better results were seen in the surgically treated patients at 1-year follow-up, the groups showed nearly equal results in terms of function 4 and 10 years later. The study demonstrated a slight tendency to a more favorable outcome with surgery.
Two days of bed rest followed by a good physical therapy program will often lead to significant alleviation of symptoms within 2 or 3 weeks. Analgesics and nonsteroidal medication may also be included in the regimen. Chiropractic adjustments should be avoided in patients with documented disk herniation. Although the role of epidural corticosteroids is unclear, they seem to be successful in decreasing the acute sciatic pain.
Approximately 10% of patients with lumbar disk herniation ultimately require surgery. Surgery is recommended if the sciatica is severe and disabling and tension signs are positive, if symptoms persist without improvement for longer than 1 month, or if findings on clinical examination and in diagnostic tests are consistent with nerve root compromise.
When a standard diskectomy is used, the overall success rate is 85%, and 95% of the patients with successful surgery return to work. Microdiskectomy minimizes the dissection and has an equally high success rate. Newer techniques using muscle-splitting approaches and small tubular retractors require even less soft-tissue violation than microdiskectomy. With this technique, only removal of the extruded part of the disk or of the free fragment is necessary. Postoperative discomfort is minimized and speed of recovery is maximized. Risks of surgery include dural tear, wrong-level exploration, hemorrhage, infection, and nerve deficit.
In cases of contained disk protrusion, percutaneous automated diskectomy or chemonucleolysis may be considered. Each of these approaches has a success rate of approximately 75%. When percutaneous diskectomy is used, a cannula is placed into the disk space under fluoroscopic control, a cutting instrument is fitted inside the cannula, and disk material is then cut and suctioned at the same time. Insertion of an optical device through an extra portal makes direct visualization of the disk possible. Although a multicenter analysis of percutaneous diskectomy showed that only 55% of patients returned to work following treatment, the success rate appears to be higher in the centers with the greatest experience.
Chemonucleolysis of herniated disks is used extensively in Europe. Chymopapain is injected into the nucleus of the contained herniated disk, and it degrades the nucleus pulposus enzymatically but leaves the annulus intact. This procedure fell into disfavor in the United States after a series of deaths occurred secondary to anaphylaxis. Other complications associated with the procedure include transverse myelitis, diskitis, seizures, and subarachnoid hemorrhage. Many of the previous bad results have been linked with poor patient selection or technical error.
Because experience with laser diskectomy is limited, this extradural approach must still be viewed as experimental. Thus far, its success rate is slightly lower than that of percutaneous diskectomy.
The facet joint is probably not a common source of pain. The term facet syndrome was introduced in 1933 by Ghormley, who thought a narrow disk space would lead to increased facet joint degeneration and serve as a potential source for sciatica. In the following decades, a distinction was made between radicular pain, which results from direct pressure on exiting nerve roots, and referred pain, which originates from the posterior spinal elements and the facet joints in particular.
Later research showed innervation of the facet joint by the medial branch of the posterior ramus of the spinal nerve. This nerve and its branches innervates the facet joints of a three-joint complex, making it virtually impossible to denervate a single joint by the injection of an agent at a single level.
The lumbar facet joints are biomechanically important. They absorb significant loads in extension and are a valuable part of the three-joint complex. Their role is to restrain excessive mobility of a spinal segment and to distribute axial loading over a broad area. In patients with symptomatic facet syndrome, biopsies have revealed cartilage changes that are similar to findings in chondromalacia patellae.
SYMPTOMS AND SIGNS
Although patients with facet syndrome tend to have problems localizing the exact source of their pain, they usually complain of low back pain that often increases on extension. The pain may radiate into the posterior thigh and commonly ends at the knee level. When patients wake up with low back pain, they frequently can alleviate the pain by changing position.
Plain radiographs demonstrate a narrowed disk space. Oblique views of the lumbar spine may show osteophyte formation of the superior and inferior facet. A more accurate study is a CT scan, which allows axial cuts and demonstration of arthritic changes involving the facets.
Conservative care with antiinflammatory medication, an external back support, and physical therapy should alleviate symptoms in most cases of facet syndrome. Intraarticular injections might be helpful as a diagnostic tool and buy time in these often difficult cases. The result of facet joint injections is unreliable, however. Medial branch ablation using a radiofrequency catheter shows some efficacy in the treatment of low back pain. However, better studies are necessary to assess accurately its overall efficacy in the management of this difficult problem. A low back fusion might be successful in extreme degenerative cases that failed to respond to conservative care, but the selection of fusion levels should not be based on the outcome of previous facet joint injections.
STENOSIS OF THE LUMBAR SPINE
Stenosis of the lumbar spine is a clinical entity responsible for a variety of complaints ranging from low back pain to lower-extremity dysfunction. The condition is defined as any developmental or acquired narrowing of the spinal canal, nerve root canals, or intervertebral foramina that results in compression of neural elements.
Some physiologic narrowing of the canal occurs with age. There are also normal variations in the cross-sectional areas and shapes of the lumbar spinal canal, with the narrowest area found between L2 and L4. The canal volume increases in flexion and decreases in extension. Narrowing of the spinal canal can further occur by bulging of the disk anteriorly, by buckling of the ligamentum flavum posteriorly, and by encroachment of the articular facets. Degeneration of the intervertebral disk causes increased stress on the facet joint and can lead to arthrosis and hypertrophy of facets and adjacent structures. This ultimately compromises the spinal canal. The decrease in canal volume occurs at such a slow and gradual pace that the neurologic structures in most patients accommodate to it, with the result that there may be surprisingly few neurologic symptoms even in patients with advanced degenerative stenosis.
The cause of pain experienced by patients with stenosis is perplexing and is attributed to mechanical, ischemic, inflammatory, and various other mechanisms. The simplest explanation, of course, is pure mechanical compression of cord and adjacent roots. The hourglass configuration and bulging of the dura as it is decompressed attests to the increased pressures within the stenotic canal. According to the neuroischemic explanation, the nerve fibers are nutritionally deprived by compression of the small nutrient vessels. Inflammatory conditions of the dura and exiting nerve roots are equally suspect. Common surgical findings are an adhesive arachnoiditis of the pia and the presence of friction neuritis, and these may constrict or tether the neural elements. The hypertrophic membranes also have reduced permeability and may obstruct the free flow of cerebrospinal fluid (CSF) from perfusing the root tissues. This can compromise the metabolism of nerve fibers because nearly 50% of their nutrients are derived from CSF.
According to a vascular and nutritional explanation for the onset of pseudoclaudication, the nerve fibers in the resting state diminish metabolic requirements that enable them to conduct sufficient impulses for minimal activity of the muscles. With increases in exertion, however, the metabolic requirements of the compromised nerve rise rapidly. The tension of root fixation and the reduced permeability to CSF hamper the delivery of necessary nutrients and the removal of noxious accumulations. The resulting relative neuroischemia renders the nerve more mechanosensitive, causing ectopic impulses to be conducted and to produce pain, paresthesias, and pseudoclaudication.
Gross morphologic changes include a compressed caudal sac, diffuse ligamentous and facet joint hypertrophy, disk space narrowing with or without concomitant protrusion, encroachment of the lamina, and occasional degenerative olisthesis. Microscopic changes include quantitative losses of neurons with numerous empty axons, various degrees of demyelinization, diffuse interstitial fibrosis with venous congestion, and coiled arterial "pigtails" on either side of the compressed lesion.
Spinal stenosis is classified as congenital or acquired. The congenital type is caused by developmental spinal anomalies that compromise the neural elements. This type is seen, for example, in patients with achondroplasia (Figure 5–11). The acquired type is more common and further divided into the degenerative, olisthetic-scoliotic, posttraumatic, and postoperative subtypes. Although the original shape of the spinal canal may be round, oval, or trefoil, the trefoil shape is most commonly associated with stenosis and may be a predisposing factor.
The location of stenosis can be central or lateral. In central stenosis, hypertrophied structures cause circumferential pressure of the spinal cord. Lateral stenosis is associated with narrowing of the foraminal canal, which is divided into three separate zones: the entrance zone, the middle zone, and the exit zone.
SYMPTOMS AND SIGNS
In degenerative spinal stenosis, which occurs primarily in elderly (more than 70 years) individuals and is seen more commonly in men than in women, the lower lumbar segments are affected the most severely. The pattern of complaints varies among patients. In many cases, there is an insidious onset and slow progression of pain in the lower back, buttock, and thigh. The pain is generally diffuse rather than neurosegmental and is episodic. Nearly all patients report that their lower extremity pain is altered by changes in position. It generally occurs with standing or walking and is relieved by rest, lying, sitting, or adopting a position of flexion at the waist. In addition, patients may find it easier to walk uphill (when their trunk is flexed) than downhill (when their trunk is extended). They may also have greater walking tolerance pushing a shopping cart because they are able to ambulate in a more flexed position. These are the hallmarks of pseudoclaudication. Neurogenic and vascular claudication may be difficult to distinguish from each other. Thus, all patients should have their distal pulses examined as a part of the overall neurologic evaluation. Mistaken diagnoses are not uncommon.
In a study of 172 patients who had symptoms of claudication, were found on myelogram and CT to have lumbar stenosis, and were treated operatively, investigators found that 65% of the patients demonstrated objective weakness and 25% exhibited diminished deep tendon reflexes. Only 10% had positive results in the straight leg–raising test, indicating entrapment of a nerve root. Nine patients had peripheral vascular disease identified by ultrasound and arteriography, and six of these nine required additional vascular bypass surgery for persistent symptoms of lower extremity claudication.
Findings on plain radiographs include degenerative disk disease, osteoarthritis of the facets, spondylolisthesis, and narrowing of the interpedicular distance as seen on the AP view. Although myelography was commonly used in the past to evaluate spinal cord or root compression, it is an invasive procedure with possible side effects and no longer used routinely. CT scanning is commonly used to evaluate the spinal elements and allows for accurate measurement of the canal dimensions when combined with contrast enhancement. A dural sac with an anteroposterior diameter of less than 10 mm correlates with clinical findings of stenosis.
MRI is comparable to contrast-enhanced CT scanning in its ability to demonstrate spinal stenosis and is now the imaging modality of choice to assess the spinal canal and the neural structures. (Figure 5–12).
A complete physical examination is essential to exclude other causes of referred pain in the low back, such as retroperitoneal tumors, aortic aneurysms, peptic ulcer disease, renal lesions, and pathologic processes of the hips or pelvis.
Psychologic factors of low back pain often give rise to symptoms independent of spinal canal narrowing and can lead to confusing differential diagnoses. Depression is common in the elderly (more than 70 years), and prompt recognition and treatment of underlying depression as the cause of somatic complaints may result in marked diminution of symptoms.
Initial management of the patient with symptoms suggestive of spinal stenosis should consist of salicylates or nonsteroidal agents and an exercise program tailored to the patient's goals or lifestyle. Surprisingly, many patients show an appreciable response to this form of treatment. Narcotics may induce dependency and should be avoided. Epidural corticosteroid injections have a short-term success rate of 50% and a long-term success rate of 25%.
If conservative methods fail, the patient's quality of life must be a key factor in deciding when to proceed with surgery. Decompressive laminectomy has a short-term success rate between 71% and 85%. Approximately 17% of older patients require reoperation for recurrent stenosis or instability. The disk should be preserved under any circumstances, to avoid postoperative instability. The best surgical results are seen in patients without coexisting morbid conditions (Figure 5–13).
Postoperative instability is reported in approximately 10–15% of patients treated. Preoperative risk factors for developing instability include disk space narrowing, osteoporosis, preexisting spondylolisthesis, and multilevel decompression. Late instability can occur when 50% of bilateral facets were resected, or when 100% of one facet joint was resected. In these cases, a prophylactic instrumented lateral fusion should be performed.
OSTEOPOROSIS AND VERTEBRAL COMPRESSION FRACTURES
Osteoporosis is characterized by a decline in overall bone mass in the axial and appendicular skeleton. The disease affects between 15 and 20 million people in the United States. Peak bone mass, attained between 16 and 25 years of age, slowly declines with age as the rate of bone resorption exceeds that of bone formation. This phenomenon occurs in both men and women and is known as senile osteoporosis. Women are also susceptible to postmenopausal osteoporosis that occurs during the 15–20 years after the onset of menopause and is directly linked to estrogen deficiency. Environmental factors also play a role in accelerating the rate of skeletal bone loss. These include chronic calcium deficiency, smoking, excessive alcohol intake, hyperparathyroidism, and inactivity. Genetic influences may also play a role.
Vertebral compression fractures are one of the most frequent manifestations of osteoporosis in the elderly (more than 60 years). Over 700,000 vertebral compression fractures occur each year. Fortunately, the overwhelming majority of patients are asymptomatic.
Patients with symptomatic vertebral compression fractures typically complain of axial pain localized to the fractured level. Occasionally, the patient's family notices that the patient's back is becoming increasingly rounded and significant loss of height has occurred. This spinal deformity is known as the dowager's hump. In general, there is no neurologic dysfunction and no radiation of the pain in any dermatomal distribution. There is often no history of significant trauma or an inciting event.
Plain radiographs and densitometric scans are the major imaging modalities in the assessment of osteoporotic bone and their pathologic counterparts (insufficiency fractures). Dual-energy x-ray absorptiometry (DXA) is the most useful of the densitometric imaging techniques because it carries a high degree of precision (0.5–2%) and subjects the patient to minimal amounts of radiation. It is also quite accurate for assessment of osteoporosis in both the axial and appendicular skeleton. Other imaging modalities include single-energy x-ray absorptiometry (SXA), quantitative computed tomography (QCT), and radiographic absorptiometry.
Posterior/anterior and lateral radiographs of the affected area of the spine are likely to reveal the location and severity of the osteoporotic fracture(s). In the thoracic spine, wedge compression fractures are most commonly encountered. In the lumbar spine, both compression and burst fractures can occur. Other imaging modalities include technetium bone scans and MRI scans. These studies should be reserved for the evaluation of fractures that remain symptomatic or progress after a course of conservative treatment. MRI is extremely useful in differentiating nonunited fractures from those that have healed and in differentiating osteoporotic fractures from those caused by malignancy.
Bone biopsy is indicated if a metabolic bone disease or a malignancy is suspected as the cause of the osteoporosis. The sample, typically retrieved from the anterior iliac crest, is examined using bone histomorphometry.
Prevention still remains the best treatment for osteoporosis. Maximizing bone mineral density prior to the onset of bone loss and minimizing the bone loss that occurs is the optimal regimen to prevent the painful sequelae of the disease. In women, estrogen replacement therapy can be initiated if there is no history of breast cancer, thromboembolic disease, or endometrial disease. Routine gynecological examination is necessary once therapy is initiated. Calcitonin therapy can be used if estrogen therapy is contraindicated. Parathyroid hormone is currently under clinical trials for the treatment of osteoporosis. Early evidence suggests that it may help to increase skeletal bone mass significantly and may be useful as a first-line treatment for severe osteoporosis.
The bisphosphonates, etidronate and alendronate, prevent osteoclastic resorption of bone. They are the only FDA-approved compounds in widespread use that increase bone mineral density. However, the increase is relatively small.
The initial treatment of symptomatic vertebral compression fractures involves a trial of analgesic therapy and bracing for comfort. Evaluation and treatment for osteoporosis can be initiated if not done already. Conservative therapy should be attempted for at least 6–12 weeks or longer if the patient is improving.
Patients who have fractures that cause neurologic deficits or significant spinal cord compression should be treated with anterior decompression and fusion followed by posterior segmental instrumentation and fusion. The poor bone quality makes correction of deformity and maintenance of posterior constructs a challenging task.
Patients who have recalcitrant back pain from a nonunited vertebral compression fracture who have failed a course of conservative management can obtain excellent symptomatic relief from fracture stabilization through injection of PMMA bone cement into the fracture through a percutaneous technique. The two most popular procedures, vertebroplasty and kyphoplasty, are both safe and efficacious. In both techniques, a cannula is inserted intrapedicularly or extrapedicularly (lateral to the pedicle) into the anterior portion of the affected vertebral body, and acrylic cement is instilled into the fractured bone under fluoroscopic control. Once the cement cures, the fracture is immediately stabilized. In the kyphoplasty technique, a balloon is inflated in the vertebral body in an attempt to compress the existing bone, create a void for instillation of more viscous cement under lower pressure, and correct the wedge deformity. This technique has the theoretical advantage of allowing some deformity correction and preventing high-pressure-related extrusion of PMMA into the spinal canal.
The mechanism of pain relief achieved through vertebroplasty and kyphoplasty is unclear. Multiple mechanisms may play a role, including fracture stabilization, denervation of pain fibers by the heat generated during the cement curing process, and neurotoxicity of the PMMA monomer. In addition, longer follow-up has raised concerns over predisposing the adjacent segment to fracture by overstiffening the affected level. These concerns are currently under active investigation.
Scoliosis is an abnormal curvature of the spine as viewed in the coronal plane. It is also generally associated with a rotational deformity, and it is the rotational component, manifested as a rib hump, prominent scapula, waist asymmetry, or lumbar fullness, that is most likely to call attention to the spinal curvature.
Etiology, Classification, & Pathophysiology
Scoliosis is classified according to its cause, with the most common causes summarized in Table 5–1. For example, if the curvature is secondary to a structural bony abnormality, it is described as congenital scoliosis. If it is caused by a neurologic disturbance or muscle disease (myopathy), it is described as neuromuscular scoliosis. If no cause can be determined, it is described as idiopathic scoliosis. The idiopathic type is the most common. Proposed etiologies for idiopathic scoliosis include abnormalities in melatonin, growth hormone or other hormones, platelet abnormalities, and posterior column abnormalities (ie, impaired proprioception and vibratory sensibility.
Particularly in idiopathic cases, scoliosis can also be classified according to the patient's age at onset. The age ranges for infantile, juvenile, adolescent, and adult scoliosis are shown in Table 5–1. Many surgeons consider juvenile scoliosis not to be a true separate entity, but rather a mix of late-presenting infantile scoliosis and early-developing adolescent scoliosis.
The curvature is named according to the side of the convexity, as well as the level of the apex, which is the most rotated vertebral body in the curve. For a cervical curve, the apex is at C1 through C6; for a cervicothoracic curve, C7 through T1; for a thoracic curve, T2 through T11; for a thoracolumbar curve, T12 or L1; for a lumbar curve, L2 through L4; and for a lumbosacral curve, L5 or lower.
The most common types of curves in cases of idiopathic scoliosis are the right thoracic curve, followed by the double curve (right thoracic and left lumbar) and the right thoracolumbar curve. The primary curve or curves are considered structural. A secondary curve, known as a compensatory curve, permits the head to be centered over the pelvis. Compensatory curves are of lesser magnitude, more flexible, and less rotated; when they become less flexible and rotation is evident, it may be difficult to determine which curve is the primary one, and indeed they may be considered structural.
The natural history of spinal curvatures is affected by factors such as the magnitude of the curve, the age of the patient, and the underlying cause of the problem. With curve progression, the deformity can become severe, leading in some cases to a so-called razor-back deformity secondary to rib rotation. With thoracic curves measuring more than 60–90 degrees (depending on the chest anterior-posterior dimension), cardiopulmonary function can become compromised, and a secondary restrictive lung disease may result from the chest deformity. Curve progression is most common during continued skeletal growth; however, it is now evident that moderate curves of 40–50 degrees should be observed for progression in adulthood. Although the extent of progression in adulthood varies widely among patients, the average amount is 1 degree per year. Taking radiographs every 2–5 years appears to be satisfactory for adults who have idiopathic scoliosis without other clinical signs of progression. The likelihood of progression is greater in patients whose scoliosis is associated with conditions such as neurofibromatosis or connective tissue diseases, including Marfan syndrome and Ehlers-Danlos syndrome.
Principles of Diagnosis
HISTORY AND PHYSICAL EXAMINATION
In a patient with a spine deformity, the history should include the age when the deformity was first noted; the manner in which it was noted (by the patient or family member, by the pediatrician or other health professional during examination or school screening, etc.); the perinatal history; developmental milestones; other illnesses; and family history of scoliosis or other diseases that may affect the musculoskeletal system. Although the incidence of scoliosis in the general population is approximately 1%, the incidence is greater in the children of women with scoliosis and particularly in the daughters of these women. For this reason, the children of women with scoliosis should be screened repeatedly throughout their preadolescent and adolescent years. Idiopathic scoliosis of the adolescent type (see Table 5–1) is more common in females, whereas that of the infantile type is more common in males.
In children and adolescents, the curvature is generally not painful. If the patient complains of pain, appropriate diagnostic tests should be performed to determine whether the curvature is secondary to the presence of a bony or spinal tumor, herniated disk, or other abnormality.
The patient's skin, habitus, and back should be carefully inspected. The presence of café au lait spots, skin tags, or axillary freckles is suggestive of neurofibromatosis. The presence of hairy patches or dimples over the spine is suggestive of spinal dysraphism. Numerous clinical syndromes are associated with scoliosis (see Table 5–1), and some of these include unusual facies. Tall, long-limbed patients may have Marfan syndrome and should be examined for high-arched palate, cardiac murmur, and dislocated lenses. Dwarfs have a high incidence of spinal deformity, both kyphosis (see section on kyphosis) and scoliosis, as well as spinal instability.
In patients with scoliosis, the shoulders or pelvis may not be level, or waist asymmetry may be noted. Most commonly, these patients have scapular prominence, with rotational deformity and rib prominence. The rib hump, or the lumbar prominence of a lumbar curve, can be accentuated by having the patient lean forward from the waist, permitting the arms to hang down; the examiner then views the spine from above or below (Figure 5–14). The rib hump can be quantified by direct measurement of its height or by using a scoliometer, which permits measurement of angular deformity. Also important in the patient's examination is measurement of decompensation, if present. This can be determined by dropping a plumb bob from the prominence of the C7 spinous process and measuring where it falls with respect to the gluteal line (Figure 5–15).
Flexibility of the curve can be qualitatively assessed by having the patient bend in the direction that effects curve correction. The spinous processes within the curve as well as the rib hump can then be assessed for flexibility of the deformity.
Patients should demonstrate a normal gait and be able to walk on their toes and heels, unless other concomitant conditions are present. Motor and sensory testing of the lower extremities should be performed, and testing of the upper extremities should also be done if the curve pattern is atypical or if a neuromuscular condition is suspected. Reflexes should be tested, and the presence of asymmetry or a pathologic reflex (eg, clonus, a positive Babinski sign, or a positive Hoffmann sign) should be noted and suggest a nonidiopathic etiology.
An asymmetric abdominal reflex is the most common neurologic abnormality noted with an intracanal lesion, such as a syrinx, diastematomyelia, or spinal cord tumor. The abdominal reflex is assessed by gently scratching each of the four quadrants of the abdomen, just a few centimeters away from the umbilicus. The response is considered normal if the umbilicus moves slightly toward the direction scratched.
Abnormal neurologic test results are an indication for further workup, such as a spine MRI, particularly if the patient has an atypical curve (eg, a left thoracic curve) or a rapidly progressive spinal deformity.
AP and lateral radiographs of the entire length of the spine should be taken, and this generally requires the use of an extra-long x-ray cassette. When the radiographs are taken, the patient should be in the standing position. If neuromuscular problems make it impossible for the patient to stand, however, radiographs can be taken with the patient sitting. Curves are measured using the Cobb method, as shown in Figure 5–16.
Views taken with the patient bending away from the concavity may be helpful or necessary, particularly if levels for fusion are being selected. These bend views allow for the assessment of the maximal correction of the curve. For curves measuring greater than 90 degrees or if the patient cannot perform the bending movement, traction films can be obtained by having two assistants exert longitudinal traction on the patient, either by grasping the legs and arms or via application of a head halter.
For severe curves (more than 90 degrees), the rotational deformity of the spine may distort the detail on an AP view. For this reason, a special Stagnara view should be obtained. The x-ray cassette is positioned parallel to the rib hump, and the x-ray beam is directed perpendicular to this to obtain an AP view of the spine, rather than of the patient (Figure 5–17).
For patients with abnormal results in the neurologic examination, atypical curve patterns, rapidly progressive curvatures, or congenital scoliosis, evaluation of the spinal canal is indicated. MRI or myelograms with CT scanning can be used. For young patients, sedation is often required. The radiologist should be advised to look for the following: a syrinx (a fluid-filled cyst within the spinal cord); a tethered cord (a fibrous band that is located distally and can prevent the normal cephalad migration of the cord); a diastematomyelia (a bony or fibrous defect that divides the spinal cord and may cause a tether); or a diplomyelia (a reduplication of the spinal cord).
If the patient has a finding of intracanal abnormalities, particularly if surgical correction of the deformity is contemplated, neurosurgical evaluation may be indicated. In many cases, the release of a tethered cord or decompression of a syrinx can be performed prior to or at the same time as the scoliosis surgery.
Patients with curves greater than 60 degrees, those with respiratory complaints, and those with scoliosis resulting from a neuromuscular cause should undergo pulmonary function testing, particularly if surgery is being considered. In cases in which pulmonary function test values are less than 30% of predicted values based on the age, sex, and size of the patient, some clinicians recommend an aggressive approach with preoperative tracheostomy placement. We prefer, however, to caution patients about the possibility of tracheostomy placement if postoperative weaning from the respirator is prolonged, and we have rarely found tracheostomy to be necessary.
Principles of Treatment
Although general principles of treatment are discussed here, additional details about treatment of idiopathic scoliosis in adults, neuromuscular scoliosis, neurofibromatosis, and congenital scoliosis are given in subsequent sections of this chapter.
Mild curves (less than 20 degrees) can generally be managed conservatively. In most cases, curves less than 10 degrees require observation only, except in very young patients who have neuromuscular scoliosis and a high risk of progression in their collapsing-type curves.
Although some skeletally immature patients with curves greater than 20 degrees require bracing, others do not. If an adolescent has less than 2 years of skeletal growth remaining, has not demonstrated progression, and has a curve that is still less than 30 degrees, the clinician may consider observation even at this point; however, considerations such as rotational deformity or a positive family history may suggest a more aggressive treatment for certain patients in this group. Any skeletally immature patient with a significant curve who shows progression of the curvature should be referred to an orthopedic surgeon with experience in treating scoliosis for possible brace treatment. Because the error of measurement of the Cobb angle is 3–5 degrees, progression of more than 5 degrees is considered significant.
Several types of braces are available for the treatment of scoliosis. The Milwaukee brace, which is also called the cervical thoracolumbosacral orthosis, can be used for nearly all curvatures, but its high profile makes it less desirable, particularly for a self-conscious adolescent. This brace (Figure 5–18) has a pelvic mold to which upright metal struts are attached. The struts are then joined to a neck ring. Corrective pads can be fastened to the metal struts, applying pressure to the rib at the apex of the convexity. If shoulder asymmetry is significant, a shoulder ring can be applied.
The thoracolumbosacral orthosis is a more cosmetically acceptable brace, but its use is limited to patients whose curves have an apex at T8 or below. The thoracolumbosacral orthosis is an external shell orthosis that is generally constructed of copolymer (largely polypropylene but with a small portion of polyethylene to prevent cracking). The shell is molded to the patient, and corrective pads are placed. One pad applies pressure at the apical rib, at the most prominent area. A second pad can be applied over the lumbar prominence if a double-curve pattern is present. If the patient shows significant decompensation to the left or right, a trochanteric extension can be included on that side to correct this tendency.
Because of the corrective forces being placed posteriorly, bracing may aggravate thoracic lordosis. For this reason, particular care should be made to place pads as laterally as possible. A decrease of normal thoracic kyphosis is common in idiopathic scoliosis and in fact contributes to the cardiovascular problems seen in patients because of the resultant decreased AP diameter of the thoracic cage.
For isolated lumbar curves, a lumbosacral orthosis can be used (Figure 5–19). Although the Boston brace is the most well-known type of lumbosacral orthosis, others are available. The various types of lumbosacral orthosis all use the corrective effect of flattening of lumbar lordosis to facilitate curve correction.
Although braces are designed to apply corrective forces to the spinal curvature and corrective effects are frequently noted on follow-up radiographs taken with the patient in the brace, braces do not afford long-term correction. Success may be achieved in preventing curve progression during the growth period of the patient and improvement may even be noted, but the curvature generally returns to the preorthotic level of severity.
Unlike most braces, the Charleston night bending brace is worn only during the night. When this brace was used in the treatment of idiopathic scoliosis, with patients braced in maximal correction only at night, early results suggested that it was as effective as full-time brace wear; however, most of the patients had not yet achieved skeletal maturity.
Infants may require casting for management of severe curves. When the patients become large enough in size, a Milwaukee brace may be used.
Patients who are wearing braces for the treatment of scoliosis should be reexamined at intervals ranging from 4 to 6 months, depending on how close they are to their growth spurt. Some clinicians prefer that patients wear their braces during follow-up radiographs, but others prefer that the braces be removed on the day of the office visit and while radiographs are taken. Generally, it is felt that full-time brace wear (23 hours a day) is best, and some studies indicate that compliance with brace wear is correlated with the success of braces. Patients may be permitted to remove the brace during athletic activities. As children grow, corrective pads may not be applying force at the appropriate area, which should be checked clinically as well as with confirming radiographs where appropriate.
If an idiopathic curvature can be controlled with bracing, bracing should be continued until the end of skeletal growth. This progress can be assessed clinically by measuring the patient's height during each office visit as well as by following the patient's history (in female patients, for example, growth generally continues for approximately 2 years after menarche). Skeletal growth can be assessed radiographically by evaluating the iliac apophysis (Risser sign, as shown in Figure 5–20) or by taking radiographs of the various physes in the wrist and comparing them with radiographs published in Gruelich and Pyle's Radiographic Atlas of Skeletal Development of the Hand and Wrist. Weaning from the brace can be begun as the patient nears the end of skeletal growth. Depending on the severity of the final curvature, follow-up radiographs may be necessary to assess the loss of correction. Some loss of correction should be expected; again, it is important not to anticipate permanent curve correction.
Curves greater than 40 degrees are difficult to control with bracing because of the greater pressures that must be exerted to effect correction. Moreover, curves greater than 50 degrees are at risk for progression, even in adulthood. When conservative treatment is not possible, several options are available for surgical intervention.
Posterior fusion and Harrington rod instrumentation was historically used. This involves placing hooks on a ratcheted rod in distraction at the ends of the curve to be fused and then performing a fusion and bone grafting. Sublaminar wiring, because of the passage of each wire around the lamina and therefore into the spinal canal at each level, carries an increased risk of neurologic complications but gives better gradual and segmental control. The sublaminar wiring technique is generally reserved for neuromuscular scoliosis patients because of the need for better fixation in the generally osteoporotic bone, as well as for other patients who may have significant osteoporosis, such as older patients (more than 60 years).
Currently, variable hook-rod systems permit placement of hooks or screws at multiple selected sites along the deformity and the application of distraction or compression, as appropriate, to correct the curve (Figure 5–21). Detailed descriptions of the various instrumentation patterns are beyond the scope of this chapter, but the basic principle is to distract on the concavity of a curve and compress across the convexity. The patient's sagittal contours can also be corrected, if needed, by applying compression to decrease kyphosis or maintain lordosis and by applying distraction to increase kyphosis. The sagittal contours can also be improved by carefully bending the rod prior to insertion so that rotation of the rod converts the coronal curve to the sagittal kyphosis if desired. The systems use a concave and a convex rod. These two rods are usually cross-linked, and they provide rigid fixation so that postoperative brace wear is not needed for most young patients.
For more rigid curves, such as may be found in older patients (over 25 years), it may be necessary to perform an anterior release and fusion as well. With an anterior approach, the disk material can be removed completely, gaining additional mobility and correction and, because an anterior fusion is then performed as well, increasing the fusion rate through this region. Additional factors that may suggest the need for anterior release and fusion include rigid kyphosis, prior failed fusion, and the presence of severe spasticity, as found in some cases of neuromuscular scoliosis. When possible, the two operations are performed at the same surgical sitting, which appears to decrease the perioperative complications. Increasing use of pedicle screws throughout the lumbar and thoracic spine appears to decrease need for anterior release and fusion in many cases.
Some single curves, particularly thoracolumbar and lumbar curves, can be treated with an anterior approach rather than with a posterior approach if desired by the surgeon. In some cases, this can decrease the number of levels fused, which is particularly desirable in the lumbar spine. Screws are placed into the vertebral body on the convex side of the curve during the anterior fusion, connected to a rod, and compression is applied to gain correction (Figure 5–22). They are generally not used lower than the level of L4 because the common iliac vessels would then lie over them and face potential erosion.
Complications & Risks of Surgery
The incidence of complications in adolescent patients is quite low, although the complications outlined here should be discussed with the parent and child during obtaining of informed consent. The risk of major complications in adult scoliosis surgery is reported to be upward of 30%, with increased rates found in association with more complex cases, older patients, and patients with coexisting medical conditions.
Among the risks faced by patients who undergo major spine fusion are paralysis and death. The incidence of paralysis, however, according to reports of the Scoliosis Research Society, is 0.4%, including both temporary and permanent deficits. Some of the neurologic risk appeared to be greater in the earlier days of using the variable hook-rod systems. These systems are powerful, and overcorrection and overdistraction can result. Because this is better understood today, the risk appears to have decreased.
Cardiopulmonary complications are unusual in adolescents, but the incidence increases in older individuals. In patients with severe pulmonary disease or a history of cigarette smoking, prolonged intubation may be required. In older patients with a preexisting disease, the risk of cardiac ischemia is increased, particularly with long surgeries, significant blood loss, and controlled hypotension as might be induced by the anesthesia team. Controlled hypotension is used to minimize blood loss during many procedures but should be tailored to what can be tolerated by a given patient.
The risk of thromboembolic complications after spine surgery ranges from 0.5% to 50%. Many surgeons use antithromboembolic hose, sequential compression boots, or low-molecular-weight heparin during and after surgery. Pharmacologic anticoagulation poses the risk of postoperative bleeding into the surgical site, which can result in an epidural hematoma and compression of the neural elements and thus should be used with caution and only in high-risk patients. Although their efficacy is well documented with hip and knee arthroplasty, benefits are not yet demonstrated for spinal surgery patients.
Although perioperative antibiotics should and usually are given, patients undergoing spinal surgery are at risk for infection. We have found prior infection, smoking history, diabetes, staged anterior and posterior spinal fusion, and increasing age to result in increased risk for postoperative infection.
Rarely occurring in the adolescent but seen occasionally in adults is pseudoarthrosis, or the failure of fusion. This can result in persistent pain or loss of curve correction. Although tomograms or bone scans are difficult to interpret because of the presence of metallic artifacts, they may help delineate suspicious areas. High suspicion for pseudarthrosis may necessitate reexploration and refusion, sometimes supplemented by anterior fusion. Instrumentation that is painful or broken may be an indication of pseudoarthrosis.
In cases of decompensation, the patient leans with the trunk shifted to one side. Decompensation, particularly in the coronal plane, can generally be attributed to overcorrection of the instrumented curves such that the flexibility of the compensatory curves is insufficient to allow righting of the patient.
FLAT BACK SYNDROME
Seen less frequently now that contoured rods are used, flat back syndrome can be a debilitating complication and reinforces the need to restore or maintain the normal sagittal contours of the spine. The distraction required to achieve curve correction by Harrington rods, when applied across the lumbar spine, flattens the normal lumbar lordosis. This can also occur if the patient is positioned such that the spine is not adequately extended. Patients may need to hyperextend their hips to stand fully upright, or a hip-flexed, knee-flexed gait may be adopted. This is generally a late complication as patients lose their ability to compensate; affected patients note increasing back fatigue or pain and the inability to stand up straight. Surgical correction of flat back syndrome has a high rate of complications, although patient satisfaction is generally high.
LOW BACK PAIN
Lower distal levels of fusion appear to correlate with increasing risk of low back pain. This raises the concern of late degeneration below the spine fusion. If the clinician can attribute a patient's symptoms to a specific unfused level, extension of the fusion may be indicated.
Idiopathic Scoliosis in Adults
Indications for intervention in adults with scoliosis are pain and progression. Painful scoliosis can be treated with conservative measures, including antiinflammatory agents and physical therapy, in an approach similar to the treatment of low back pain without a deformity. Bracing of the curvature is rarely indicated because these patients have no skeletal growth remaining; however, a patient who cannot tolerate surgery for medical reasons may be braced as a salvage measure. In an otherwise reasonably healthy patient, if progression greater than 5 degrees can be documented or if symptoms are refractory to conservative measures, surgical correction may be indicated.
The same surgical principles apply to adults as younger patients. Adults are more likely to have rigid curves, which may require a combined anterior and posterior approach. Depending on the deformity and region of pain, fusion to the sacrum may be indicated. Patients with significant leg pain should have preoperative CT scanning or MRI to assess whether spinal stenosis accounts for the symptoms and warrants surgical decompression.
In adulthood, previously compensatory curves are often structural. It is important to consider the flexibility of all curves present in adult patients, including the fractional curve between L4 and the sacrum. (A fractional curve is one that does not cross the midline, such as that measured between a tilted L4 endplate and the horizontal and midline sacrum.) The preoperative bend films of all curves should be reviewed and the following question addressed: If correction of the major curve or curves is achieved as would be predicted by the curve flexibility, will the patient still be able to stand centered head over pelvis? If not, the clinician may need to consider fusing a lesser curve to balance the spine.
Another concern is the need to correct sagittal plane deformity, particularly kyphosis, or maintain normal sagittal contours.
Anterior release and fusion may be indicated prior to posterior instrumentation in some cases to permit the patient to stand upright with the head over the sacrum and the knees and hips straight. Before subjecting a patient to the significantly greater surgical risk of a combined anterior and posterior procedures, however, the surgeon should take into account issues such as spinal stenosis, hip disease, and pain from the patient's condition that may affect the patient's ability to stand fully upright.
For older patients, particularly women, osteoporosis may prevent optimal fixation of the instrumentation to the spine. Sublaminar wires, as previously mentioned, can improve the rigidity of the fixation because the multiple sites of attachment spread the load over more bony attachments. There is, however, a theoretical increase in risk of neurologic damage during surgery when this approach is used.
Use of iliac screws (Figure 5–23) should be considered for long fusions to the sacrum because it appears best at resisting flexion moments that are experienced at the lumbosacral junction. In complex and difficult cases such as the one discussed here, surgery should only be undertaken for relatively healthy patients who have failed to respond to nonoperative intervention and who have a clear understanding of the goals and the significant perioperative risks of surgery.
Postoperative care in the adult patient undergoing major reconstructive surgery requires detailed attention to the patient's systemic needs, much more so than is generally required by patients undergoing other orthopedic procedures. Those patients who require thoracotomy or thoracoabdominal approaches will have postoperative chest tubes and are at higher risk for pulmonary complications.
Fluid shifts can be significant after lengthy procedures, particularly those with large blood losses. Anterior approaches, although largely retroperitoneal, can lead to prolonged ileus, a problem compounded by the use of postoperative narcotics that all orthopedic patients require.
Neuromuscular conditions frequently associated with scoliosis include muscular dystrophy, cerebral palsy, poliomyelitis, spinal cord tumor, spinal cord trauma, spinal muscular atrophy, Friedreich ataxia, syringomyelia, familial dysautonomia, and myelomeningocele (spina bifida). Spinal deformities tend to present early in life in patients with these conditions and often progress to severe deformities because of muscle weakness and the many years of ensuing growth. Although neuromuscular scoliosis can be subdivided into neurogenic and myogenic types (see Table 5–1), the principles of treatment for the two types are the same.
The assessment of patients should be detailed and include an evaluation of overall function, mental status, motor strength, ambulatory status, and sitting tolerance as well as a search for the presence of problems such as joint contractures, pelvic obliquity, and pressure sores. Joint contractures can lead to pelvic obliquity or can limit the patient's ambulatory or sitting ability. Pelvic obliquity or a dislocated hip can be primary and lead to scoliosis or can be secondary to the spinal deformity. The primary condition should be determined, and if corrected sufficiently early, may obviate or delay the need for further corrective surgery.
With neuromuscular scoliosis, as with idiopathic scoliosis, curvatures affecting the thoracic spine and therefore the chest cage can have adverse effects on the pulmonary system, which is already compromised in most neuromuscular scoliosis patients because of weakness of the respiratory musculature. Truncal imbalance or pelvic obliquity, or both, are often associated with neuromuscular scoliosis and can impair ambulatory ability or sitting balance in affected patients. Before treatment of neuromuscular scoliosis is undertaken, the goals should be understood by the clinician as well as the patient and family. In many cases, the conditions are progressive, and the long-term prognosis for the patient and the patient's curvature should be considered. Stabilization of a curvature clearly does not affect the disease process and therefore does not affect the life expectancy of the patient.
Studies show, however, that in patients with Duchenne-type muscular dystrophy, thoracic curvatures contribute in themselves to loss of pulmonary function, beyond that which would be experienced by the generalized loss of pulmonary function associated with the progressive weakness of the respiratory muscles. In patients with Duchenne-type muscular dystrophy, an increase of 10 degrees in thoracic scoliosis results in a loss of 4% of functional vital capacity.
The neuromuscular condition associated with scoliosis in each case should be well delineated and understood because the curvatures in neuromuscular scoliosis have a higher likelihood of progression than those in idiopathic scoliosis, given the factors of muscle weakness, muscle imbalance, progression of disease, and the generally younger age at which the curves in patients with neuromuscular conditions are diagnosed. Particularly as pulmonary function is also progressively lost in many neuromuscular conditions, a more aggressive surgical approach is generally recommended, with intervention performed once the probable curve progression is established (by history, diagnosis, or degree of curvature) and preferably while the pulmonary function is still relatively good.
Unlike patients with idiopathic scoliosis, patients with neuromuscular scoliosis do not experience the active corrective effect of a brace. Instead, the brace functions as a shell of support, counteracting the effect of gravity on the collapsing spine. Bracing may adversely affect the breathing of these compromised patients but may slow progression in very young (less than 10 years) patients or while the course of the disease is being determined.
If surgery is recommended in cases of neuromuscular scoliosis, special concerns include whether the bone is osteoporotic, whether pelvic obliquity is present, and whether the patient has sitting balance. Osteoporotic bone often necessitates the use of sublaminar wiring, despite the theoretically increased neurologic risk associated with passage of the wire into the spinal canal. If pelvic obliquity exists or if the patient has poor sitting balance, fusion to the pelvis is advisable. This may be performed with the Galveston technique, in which the ends of a specially bent rod are placed between the inner and outer tables of the iliac wing. The proximal rod ends are then placed on either side of the spine after being bent to appropriate sagittal contours. The rods are subsequently attached to the spine with the sublaminar wires. Because of the collapsing nature of the spine in cases such as those described here, it is usually necessary to extend the fusion proximally to T3 or T4 to prevent kyphosis from developing above the fusion. Because sublaminar wires do not provide axial control, rigid proximal fixation, either hooks or screws, is recommended at the proximal end of the construct.
The perioperative management of neuromuscular scoliosis can be complex, and these patients often benefit from a multidisciplinary approach involving the orthopedic surgeon, pulmonologist, pediatrician, anesthesiologist, physical and occupational therapists, and additional specialists, depending on other system involvement. Patients with Duchenne-type muscular dystrophy, for example, may also develop cardiomyopathy. Those with Friedreich ataxia have a high incidence of cardiomyopathy and diabetes mellitus.
With aggressive medical and surgical management and a supportive family, the longevity and quality of life for patients with neuromuscular scoliosis can be optimized.
Spinal deformity associated with neurofibromatosis poses some special considerations. Curvatures seen in affected patients may be of the idiopathic type or the dysplastic type. Curvatures of the first type exhibit the same curve patterns as seen in patients with idiopathic scoliosis and are most commonly right thoracic curves and may be managed in a similar manner. Curvatures of the second type can be much more malignant in behavior.
Dysplastic curves can be identified by evidence of dysplastic bone: penciling of the ribs or transverse processes, enlargement of the foramina, erosion of the vertebrae, and evidence of a shorter, more abrupt curve than that seen in idiopathic scoliosis. Dysplastic curves usually are associated with kyphosis, which also exists through a fairly short sharp segment. They may occur in the thoracic, thoracolumbar, or lumbar spine.
Dysplastic curves in patients with neurofibromatosis can progress rapidly and lead to severe deformity. Bony erosion can occur secondary to neurofibromas or to dural ectasia (expansions of the dural sac, which can account for enlargement of the foramina or erosion of the vertebrae). The short kyphotic curves and erosion of bone can in severe cases result in neurologic impairment, including paraplegia.
Surgery in patients with dysplastic curves is associated with a high incidence of pseudarthrosis. If surgery is indicated, it is usually recommended to perform both an anterior and a posterior fusion. This combined approach results in a satisfactory fusion rate of up to 80%. Because of the dysplastic bone stock, it may be necessary to use a combination of sublaminar wires, hooks, and screws. Preoperative MRI may be useful in assessing the extent of dural ectasia. Fusion levels are selected according to the end vertebra of the curvature. The end fusion level must lie centered over the middle of the sacrum, much like the selection for idiopathic scoliosis. Clearly, however, the fusion should not end above or below a dysplastic vertebra, although it would be rare for such a level not to be within the curve.
Congenital scoliosis is caused by one of two types of structural bony abnormality (Figure 5–24). Type I is a failure of formation, such as that seen with hemivertebrae. Type II is a failure of segmentation, such as that seen with block vertebrae and that seen with unsegmented bars, where there is a tether to growth on one side of the spine. Mixed abnormalities are also found in patients with congenital scoliosis. Unilateral unsegmented bars with contralateral hemivertebrae have the greatest tendency for rapid progression and should be surgically fused as soon as the bony abnormality is evident. Unilateral unsegmented bars also tend to progress.
With respect to progression, hemivertebrae have a variable prognosis, depending on whether a contralateral hemivertebra is present that results in overall balance of the spine, whether multiple hemivertebrae are on one side of the spine, and how much growth potential is predicted for each endplate of the hemivertebra. Hemivertebrae at the cervicothoracic junction and the lumbosacral junction have a relatively poor prognosis because the spine above or below the abnormality cannot compensate. Hemivertebrae should be observed so as to delineate their growth potential and progression.
Bracing is ineffective in treating congenital scoliosis because the curves are inflexible. Bracing is sometimes used to prevent progression of the compensatory curve, however.
In patients with congenital scoliosis, the incidence of cardiac abnormalities is increased, as is the incidence of renal abnormalities (20–30%) and intracanal abnormalities (10–50%). Abdominal ultrasound or other imaging tests should be used to rule out absent or abnormal kidneys. Intracanal abnormalities may include a syrinx (cyst within the cord), diastematomyelia or diplomyelia (division or reduplication of the cord, respectively), and tethered cord (presence of a tight filum terminale that does not permit the conus medullaris to migrate upward normally with growth).
If surgical intervention in patients with congenital scoliosis is indicated, several options are available. Fusion in situ is the simplest procedure. For very young (less than 10 years) patients, however, a posterior fusion alone results in tethering of the posterior elements while the anterior elements continue to grow. This situation may lead to the crankshaft phenomenon, whereby the anterior growth in the spine results in a twisting deformity around the fused posterior elements. For this reason, combined anterior and posterior fusion is usually recommended for very young patients, halting growth circumferentially about the spine. (The crankshaft phenomenon can also occur in very young patients with noncongenital forms of scoliosis who were treated by posterior fusion. Age younger than 10 years, Risser stage 0 or 1, and the presence of an open triradiate cartilage are indicators of skeletal maturity at risk for development of crankshaft.)
In some cases of hemivertebra, hemiepiphysiodesis may be performed, arresting growth on the curve convexity but permitting continued growth on the curve concavity, with resultant gradual curve correction. This procedure has good results in selected patients but can be unpredictable with respect to the amount of actual correction that can be achieved.
In cases in which a hemivertebra is accompanied by significant coronal decompensation and compensatory growth would not be adequate to result in spinal balance, consideration can be given to hemivertebra excision via a combined anterior and posterior approach. Although this procedure is technically more demanding and has greater potential risks, it allows for better overall curve correction and improvement of coronal balance. Hemivertebra excision may be the preferred option in the lumbar spine or lumbosacral junction, where the neurologic risk is to the cauda equina rather than the spinal cord and where oblique takeoff of the vertebra above the hemivertebra can result in significant truncal decompensation.
The normal sagittal contour of the spine includes cervical lordosis, thoracic kyphosis, and lumbar lordosis (Figure 5–25). Increases or decreases in any of these can be seen. If they are severe enough, they can cause disability, as discussed later in the cases of congenital kyphosis and Scheuermann kyphosis.
As in congenital scoliosis (see previous discussion), congenital kyphosis can result from a failure of formation or a failure of segmentation. In congenital kyphosis, however, failures of formation have a much more dangerous clinical prognosis. These can lead to congenital or progressive "dislocation" of the spinal column (Figure 5–26) and paralysis if not treated appropriately. If performed early enough, posterior fusion may be sufficient to prevent neurologic problems. Severe deficiencies, however, may require anterior and posterior fusion to achieve stability.
Normal thoracic kyphosis ranges from 25 to 45 degrees. Postural kyphosis can increase this curvature, but if no abnormalities are present, the curve is flexible and the posture can be easily corrected by the child. If endplate abnormalities are present and three or more vertebral bodies are wedged as seen on the lateral radiograph, the diagnosis of Scheuermann kyphosis can be made. Schmorl nodules, characterized by herniation of the disk material at the vertebral endplates, and increased thoracic kyphosis are also seen. Clinically, patients with this type of kyphosis have a curvature that is more abrupt than that observed in people with postural roundback, and this type is only partly correctable by forced extension. It can be demonstrated either by having the patient hyperextend or by taking a lateral radiograph with the patient lying over a pad at the apex of the kyphosis so the Cobb angle can be measured. Thoracic curves may cause pain and discomfort, although some report that pain is more commonly seen in thoracolumbar curves.
Bracing can be instituted if the kyphosis measures more than 45 or 55 degrees in a skeletally immature patient, particularly if the curvature is progressive or accompanied by pain. If lesser degrees of deformity are symptomatic, they can be treated with physical therapy exercises and observed for progression. Brace treatment requires the use of the Milwaukee brace, with two paraspinal pads placed over the apical ribs posteriorly. Radiographs should be taken with the patient in the brace to confirm that adequate correction is being effected. The brace can be removed for sports and bathing but should otherwise be worn 23 hours a day. Repeat lateral radiographs should be taken at intervals of 4–6 months. If bracing is successful at controlling the curve, it should be continued until the patient nears skeletal maturity. Weaning should be performed slowly, so as to maintain correction. Although some correction may be lost, proper use of the Milwaukee brace can result in long-lasting improvement in many patients with kyphosis (which is not the case with brace treatment of adolescent idiopathic scoliosis).
Surgical treatment of kyphosis may be indicated if the curve magnitude increases despite bracing, if the patient has significant associated symptoms, or if the patient who is nearing skeletal maturity has a severe curvature. Posterior spinal fusion with a variable hook-rod system, such as the Cotrel-Dubousset system, is the treatment of choice in these cases. If the curve flexibility does not permit adequate correction as demonstrated on a hyperextension lateral radiograph, an anterior release and fusion prior to the posterior spinal fusion is indicated.
Reports describe the natural history of Scheuermann kyphosis, suggesting some functional limitations but little actual interference with lifestyle. The deformity can worsen over time. It appears clear, however, that many patients have their symptoms of back pain and deformity improved by surgery. Proper patient education and selection are essential for appropriate treatment of these patients.
Neural tube defects can result in complex spinal deformities secondary both to the neuromuscular collapsing nature of the spine and to the vertebral anomalies that can give rise to congenital kyphosis or congenital scoliosis. Myelomeningocele or meningocele is present at birth in a patient whose neural tube failed to close in utero. Sac closure is usually performed shortly after birth. In many cases, the affected infant also requires placement of a ventriculoperitoneal shunt because of hydrocephalus. The level of neurologic function usually corresponds to the level of the defect. For example, a low thoracic myelomeningocele patient has no lumbar nerve roots functioning and therefore no lower extremity function. An L4 myelomeningocele patient has a functioning tibialis anterior but no extensor hallucis and no gastrocnemius and usually no voluntary bowel and bladder control.
Neurologic function in patients with myelodysplasia is static and should not deteriorate with growth. Neurologic changes, especially during growth spurts, require evaluation for tethered cord, a common occurrence in affected children.
Orthopedic management includes maximizing the function of patients through the use of braces, ambulatory aids, wheelchairs, or surgery. The degree of spinal deformity is related to the neurologic level, with spinal collapse more likely in those with a higher neurologic level of involvement than in those with a lower level. The presence of bony abnormalities can affect this prognosis, of course.
As with many neuromuscular spinal deformities, curvatures may present early in life. If the clinician elects to treat a patient with bracing, it is important to remember that bracing in the presence of insensate skin can result in pressure sores if the brace is not adequately padded and the parents are not instructed regarding skin care.
In many cases, the curvature eventually requires surgical stabilization. Because of the magnitude and stiffness of the curvature as well as the absence of posterior elements, the preferred treatment is anterior and posterior fusion. Anterior instrumentation may improve rigidity of the surgical construct. In patients with myelodysplasia, fusion to the sacrum is invariably required because of pelvic obliquity or lack of sitting balance. Luque-Galveston instrumentation to the proximal thoracic spine is preferred, as with many neuromuscular deformities.
The lack of posterior elements in the myelodysplastic spine can lead to congenital kyphosis. Although kyphosis in these patients does not compromise neurologic function, it can lead to pressure sores over the prominent area. The treatment of choice for this problem is posterior kyphectomy and fusion.
SPONDYLOLISTHESIS & SPONDYLOLYSIS
Spondylolisthesis is the slipping forward of one vertebra upon another. Spondylolysis is characterized by the presence of a bony defect at the pars interarticularis, which can result in spondylolisthesis.
The classification system most commonly used in spondylolisthesis was originated by Wiltse et al. in 1976 and subsequently modified by others. Type I, the dysplastic form of spondylolisthesis, is a congenital deficiency of the superior sacral facet, the inferior fifth lumbar facet, or both. Type II, the isthmic form, is caused by a defect in the pars interarticularis but can also be seen with an elongated pars. Types I and II are most commonly seen in younger (less than 15 years) patients and most likely to occur at the L5-S1 level. Type III, the degenerative form of spondylolisthesis, is seen in older patients and most frequently involves the L4-L5 level. Type IV, the traumatic form, is located other than at the pars. Type V, the pathologic form, is caused by conditions such as a neoplasm. The Wiltse classification of spondylolisthesis is shown in Figure 5–27.
Marchetti and Bartolozzi proposed a classification of spondylolisthesis that separates developmental and acquired types of spondylolisthesis. Developmental spondylolisthesis is divided into high dysplastic and low dysplastic types, with each of these subdivided into those with lysis of the pars interarticularis or elongation of the pars interarticularis. Acquired types include degenerative, traumatic, postsurgical, and pathologic. A new classification based on clinical presentation and spinal morphology is now suggested for children and adolescents.
The cause of isthmic spondylolisthesis may be developmental, with a congenital defect of dysplasia predisposing some individuals to spondylolysis. The overall incidence of spondylolysis is approximately 6%. The high incidence of spondylolysis in gymnasts, football players, weight lifters, and other athletes who place their lumbar spines in hyperextension suggests that repetitive injury may be a contributing mechanism. Biomechanical studies also suggest that the pars interarticularis is under the greatest stress in extension.
Spondylolysis and spondylolisthesis may be asymptomatic, or they may present with back pain and leg pain. Rarely, they present with radicular symptoms or bowel and bladder symptoms. Isthmic spondylolisthesis most commonly presents during the preadolescent growth spurt, between 10 and 15 years of age. The extent of slippage may not be correlated with the severity of pain. The L5 pars interarticularis defect, with resultant slippage of L5 forward on the sacrum, is most commonly seen.
In young patients, regardless of the extent of slippage, there may be tight hamstrings and a knee-bent, hips-flexed gait, the classic Phalen-Dickson sign. Careful palpation of the spine of the patient with spondylolisthesis may reveal a step-off secondary to the prominent spinous process of L5. With more severe slippage, the lumbosacral junction becomes more kyphotic and the trunk appears shortened, with the rib cage approaching the iliac crests (Figure 5–28).
Radiographic examination shows the defect on the lateral view, with the percentage of slippage measurable from this view. The Meyerding classification is most commonly used (Figure 5–29). Oblique radiographs demonstrate the "collar" or "broken neck" on the "Scottie dog" (Figure 5–30). If a unilateral defect is present, the contralateral pars or lamina may show sclerosis. If the history is suggestive of an early stress fracture and radiographic findings are negative, bone scans may be useful. CT scanning shows spondylolysis as an incomplete ring.
The slip angle, a measure of lumbosacral kyphosis, is useful in determining the likelihood of progression to higher grades of slippage in patients. A line is drawn along the posterior cortex of the sacrum, and the angle between its perpendicular and a line drawn along the inferior border of L5 is measured (Figure 5–31). If the slip angle is greater than 50 degrees, the likelihood of progression is high.
In patients with radicular symptoms or bowel or bladder impairment, CT scanning or MRI is essential if surgical intervention is considered.
Low-grade spondylolisthesis (Meyerding grade I or II) can usually be managed with conservative measures, including restriction of the aggravating activity, bracing to reduce lumbar lordosis, and physical therapy. Patients with grade I slips who respond to conservative therapy may be permitted to resume all activities. For those with grade II slips who are improved with conservative treatment, it is usually recommended that they refrain from activities that hyperextend the spine. Skeletally immature patients with grade III or higher slips are at significant risk for progression, and they are recommended for fusion.
Fusion and Decompression
Fusion is indicated for patients who fail to respond to conservative measures, demonstrate progression, or have greater than 50% slippage and are skeletally immature. For most patients, fusion in situ is indicated. If slippage is less than 50%, fusion from L5 to S1 is sufficient. If slippage is greater than 50%, it is necessary to fuse from L4 to S1 to achieve a fusion bed that is under compression. Intertransverse fusion can result in fusion rates of 95% and good to excellent clinical outcomes in 75–100% of patients. This technique can be performed through two parallel paraspinal skin incisions. Alternatively, a midline skin incision with paraspinal fascial incisions, approximately two fingerbreadths off the midline, can be employed. The sacrospinalis fibers can be split, and access to the transverse processes is obtained. The transverse processes, pars interarticularis, facet joint, and adjacent lamina are exposed and decorticated. Iliac crest bone graft is harvested and placed in corticocancellous strips over the fusion bed (Figure 5–32).
If neurologic findings such as numbness, leg pain, leg weakness, or bowel and bladder compromise are present, decompression may be needed. Central and foraminal stenosis can be evaluated with a CT scan or MRI. In many cases, fibrocartilaginous scarring at the site of the pars defect accounts for the compressive symptoms. Particularly for young (less than 18 years) patients, an isolated decompression without fusion is likely to result in slip progression, so decompression should be combined with fusion. Some reports indicate that signs of nerve root irritation, including hamstring tightness, resolve when fusion is used without surgical decompression. It may take up to 18 months for these signs to resolve after fusion alone.
Bracing or casting may be indicated after fusion and may consist of the use of a lumbar corset, a thoracolumbar orthosis, or a thoracolumbosacral orthosis with leg extension or pantaloon spica cast, depending on the preference of the surgeon. Once the patient's fusion is solid, full activities are permitted.
Pars repair may be indicated for young (less than 18 years) patients who have single-level or multiple-level L1-L4 pars defects without evidence of disk damage. Screw fixation or wiring of the transverse process to the spinous process (Figure 5–33) yields good results in appropriately selected patients.
Fibular Strut Graft
Bohlman and Cook described a technique for one-stage posterior decompression and interbody fusion for treatment of grade V spondylolisthesis (spondyloptosis). After wide decompression, a drill hole is prepared between the L5 and S1 nerve roots, passing through the sacrum to the L5 vertebral body that has slipped in front of the sacrum. The configuration is similar to that diagrammed in Figure 5–34 for anterior strut graft fusion. Autograft or allograft fibula is inserted and then countersunk to avoid dural impingement. Posterolateral fusion is also performed at this time.
Another option for achieving fusion is via an anterior transperitoneal or retroperitoneal approach. The surgeon can either perform disk space grafting with tricortical iliac crest or place a fibular graft through a drill hole from the L5 vertebral body to the sacrum (see Figure 5–34). For high-grade slips, anterior fusion places the graft in compression. Clearly, there are significant risks with the anterior approach, including the risk of vascular damage in male and female patients and the risk of retrograde ejaculation secondary to damage of the sympathetic nervous system in male patients. Because of these risks and because good results can generally be achieved with posterolateral fusion, anterior fusion is best reserved for patients with high-grade slippage or patients who have undergone unsuccessful posterior arthrodesis treatment.
Reduction of high-grade spondylolisthesis remains controversial but may be considered in patients who have high-grade slippage and are unable to stand balanced with their head over the sacrum while keeping their knees straight. Reduction can improve the patient's overall trunk appearance, which is characterized by a short waist, transverse abdominal skin fold, and heart-shaped pelvis, all of which become more prominent with high-grade spondylolisthesis. Improvement of the slip angle may prevent slip progression.
Although even fusion in situ of high-grade slips can lead to neurologic compromise and cauda equina syndrome, concern is raised over the neurologic risk with reduction techniques. Closed reduction using halo-pelvic or halo-femoral traction allows for gradual reduction while permitting the awake patient to have repeated neurologic assessments. It is less commonly used because of the availability of smaller pedicle screws. A posterolateral fusion can be performed after traction is completed or initially at the time of decompression. Anterior fusion may or may not be indicated, depending on the particular patient and on the reduction achieved.
Pedicle screw instrumentation can be used by experienced surgeons to distract and then posteriorly translate the slipped vertebra. Neurologic complications may occur but in most cases are temporary. Supplemental techniques, such as intrasacral rods with iliac buttressing, or iliac screws, appear to improve distal fixation as does performing an interbody fusion.
For severe slips, L5 vertebrectomy with reduction of L4 onto S1 is successfully performed. The technique shortens the spine and therefore theoretically poses less neurologic risk, but surgical manipulation of the nerve roots and posterior translation of L4 can result in neurologic compromise such as footdrop.
As noted earlier, neurologic compromise sometimes results even after fusion in situ. Particularly with decompression alone (which is rarely indicated) but also with high-grade slips even after fusion, progression of the slip can occur. This happens if there is pseudarthrosis (failure of fusion), but slippage can also occur postsurgically before the fusion becomes solid, or the fusion mass can bend if the forces across it are sufficiently great.
Incomplete pain relief is rare in adolescents but is sometimes a complaint of adults. The reasons for this are not entirely clear, but it is noted that secondary degenerative changes can occur either at the level of the spondylolisthesis or at the level above.
Unlike isthmic spondylolisthesis, degenerative spondylolisthesis is found more commonly at the L4-L5 level, secondary to a number of factors. This level sees more stresses than other lumbar levels because the L5-S1 level is protected by the strong transverse-alar ligaments that run from the transverse process of L5 to the sacral ala and also because the lumbosacral junction usually lies below the iliac crest and is additionally protected from motion. Other lumbar levels have more motion segments above and below to disperse stress. With degeneration at the disk and facet joints occurring at a somewhat greater rate, narrowing of the disk can occur. Because of the configuration of the facet joints and the lumbar lordosis, this results in some slippage forward of the vertebral body upon the one below. Note that without surgical removal of the posterior elements, degenerative spondylolisthesis rarely reaches the severity seen in severe isthmic spondylolisthesis.
The narrowing at the disk level can lead to increased stresses at the facet joints, with resultant degenerative facet disease, including joint narrowing and hypertrophy of the facets. As this cycle continues, the hypertrophied facets and the redundant ligamentum flavum can result in spinal stenosis. The forward displacement of one vertebra upon the other can further narrow the canal.
Most patients with degenerative spondylolisthesis demonstrate symptoms of spinal stenosis with dysesthesias or leg pain. The spinal stenosis pattern of pain when walking beyond a well-defined distance (neurogenic claudication) is often present, relieved only by sitting down or bending over.
If degenerative spondylolisthesis is refractory to conservative measures (described earlier for isthmic spondylolisthesis), surgery may be indicated. Surgical intervention should consist of decompression. Fusion enhances surgical results after decompression for degenerative spondylolisthesis. Instrumentation such as pedicle screws may enhance fusion rates and prevent further slippage during the postdecompression period before the fusion consolidates.
Thoracic Disk Disease
Disk herniation is found much less commonly in the thoracic spine than in the cervical and lumbar spine, presumably because of the decreased mobility seen in this region with the rib cage and sternum. Herniated thoracic disks account for 1–2% of operative disks, although the reported incidence in autopsy series is 7–15%.
Patients with thoracic disk disease may present with radicular symptoms at the level of involvement and complain of back or lower extremity pain, extremity weakness, numbness corresponding to the level of the disk herniation or below, and bowel or bladder dysfunction. They may demonstrate a spastic gait, with long-tract signs, if the disk is more central. Diagnosis is made by myelography, sometimes in conjunction with CT scanning or MRI.
In the absence of long-tract signs and paraparesis, conservative measures may include rest, antiinflammatory medications, and physical therapy, with a 70–80% success rate.
Surgical treatment is recommended for patients with signs of myelopathy, including paraparesis or hyperreflexia. Decompression is most safely performed via an anterior approach. The anterior extrapleural approach is advocated and yields good results.
When an anterior approach is used, 58–86% of patients show neurologic improvement and 72–87% experience pain relief. Neurologic deterioration is reported in up to 7% of patients who undergo surgery via an anterior or anterolateral approach and in 28–100% of patients who undergo posterior decompression. Posterior laminectomies are associated with a high rate of complications, including worsening neurologic function from manipulation of the cord and incomplete decompression of an inadequately visualized disk.
The cervical spine is the most mobile area of the spine, and as such it is prone to the greatest number of injuries. Injuries to the cervical spine and spinal cord are also potentially the most devastating and life altering of all injuries compatible with life. In the United States, approximately 10,000 spinal cord injuries occur each year. An estimated 80% of the victims are younger than 40 years, with the highest proportion of injuries reported in those between 15 and 35 years of age. Approximately 80% of all people who suffer from spinal column injuries are male. Falls account for 60% of injuries to the vertebral column in patients older than 75 years. In younger patients, 45% of injuries result from motor vehicle accidents, 20% from falls, 15% from sports injuries, 15% from acts of violence, and the remainder from other causes.
With the use of seat belts and air bags in motor vehicles and the advent of trauma centers and improved emergency service awareness of potential cervical injuries, fewer patients with cervical spine injuries are dying secondary to respiratory complications. The approach in treating these patients is early recognition of cervical spine injuries with rapid immobilization to prevent neurologic deterioration while the evaluation and treatment of associated injuries are carried out. After the patient is stabilized, the goals are restoration and maintenance of spinal alignment to provide stable weight bearing and facilitate rehabilitation.
Identification & Stabilization of Life-Threatening Injuries
Eighty-five percent of all neck injuries requiring medical evaluation are a result of a motor vehicle accident. Many of the affected patients are multiple-trauma victims and therefore may have more urgent life-threatening conditions. The ABCs of trauma are followed in order of priority, with airway, breathing (ventilation), and circulation secured before further evaluation proceeds. Throughout the evaluation of other body systems, the cervical spine should be presumed injured and thus immobilized. Approximately 20% of patients with cervical trauma are hypotensive upon presentation. The hypotension is neurogenic in origin in approximately 70% of cases and related to hypovolemia in 30%. Concomitant bradycardia is suggestive of a neurogenic component. Another finding suggestive of cervical spine injury is an altered sensorium secondary to head trauma or lacerations and facial fractures. Appropriate diagnosis and fluid management are critical in the early hours of postinjury management. After all life-threatening injuries are identified and stabilized, the secondary evaluation, including an extremity examination and neurologic examination, can be safely carried out.
History & General Physical Examination
Details of the history of the injury should be obtained. If the patient is conscious, much of the information can be obtained directly. If not, family members or witnesses of the injury should be questioned. In the case of a motor vehicle accident, for example, pertinent questions include the following: Which part of the patient's body was the point of impact? Was the patient thrown from the car? Was there head trauma or a loss of consciousness? Were there any transient signs of paresis? Was the patient able to move any of his or her extremities at any time following the accident and before loss of function? What were the speeds of the involved motor vehicles? Was the patient restrained with a seat belt? Did an air bag deploy?
The history taken from the patient or family members should also include information about preexisting conditions such as epilepsy or seizures and about preexisting injuries. If the patient had any previous radiographic examinations, the radiographs might be useful for comparison.
It is helpful to question patients about what they are experiencing at the time of the examination. Are there areas of numbness, paresthesia, or pain? Can they move their extremities? The examiner should then proceed with the physical evaluation, beginning by observing the face and head of the patient for any areas of potential injury and attempting to determine the potential mechanism of injury. For instance, any lacerations or contusions to the forehead might indicate a hyperextension type injury. Observation should next include watching the extremities for any signs of motion. A genital examination should be performed because a sustained penile erection may be indicative of severe spinal cord injury. Then without moving the patient, palpation can be performed. Although palpation can be helpful in identifying potential levels of injury of the spine, it should not be used as the sole screening examination because false-negative results are possible.
A meticulous neurologic examination should be performed following the history and general physical examination.
The neurologic evaluation should start with documentation of the function of the cranial nerves, working proximally to distally. Observation is particularly important in the unconscious patient. Spontaneous motion in an extremity may be a sole source of information regarding spinal cord function. Respiratory efforts made with intrathoracic musculature versus abdominal musculature are also significant. In the conscious patient who is able to follow commands, a motor examination should be fairly straightforward. Rectal and perirectal sensations should be documented because these may be the sole signs for distal spinal cord function.
An extensive sensory examination should also be performed with careful attention to dermatomal innervation. In the acute setting, it is useful to document sharp and dull sensations as well as proprioception. Sharp and dull sensations are carried via the lateral spinothalamic tract, whereas proprioception is carried through the posterior columns. Sharp and dull sensations are effectively tested with the sharp and blunt ends of a pen, and proprioception is tested by having the patient verify the position of the large toe and other joints as the examiner places them in dorsiflexion and plantarflexion. It proves helpful to make ink markings directly on the patient's skin to show the level of the dermatomal deficit, which decreases the chance for intraobserver or interobserver error over sequential examinations.
Reflexes should be checked bilaterally. In the upper extremity, the biceps reflex at the flexor side of the elbow evaluates the C5 nerve root, and the brachioradialis stretch reflex at the radial aspect of the forearm just proximal to the wrist checks the C6 nerve root. The triceps reflex is innervated by C7. In the lower extremity, the knee jerk reflex is innervated by L4, and the ankle jerk is innervated by S1.
The presence or absence of the four reflexes listed in Table 5–2 should be checked. The Babinski reflex (plantar reflex) is evaluated by firmly stroking the lateral plantar aspect of the foot distally and then medially over the metatarsal heads and then observing the toes. If the toes flex, the response is considered negative (normal). If the toes extend and spread, the response is considered positive (abnormal) and indicative of an upper motor neuron lesion. The bulbocavernosus reflex has its root in the S3 and S4 nerves and is evaluated by squeezing on the glans in a male patient or applying pressure to the clitoris in a female patient. This action should elicit a contraction of the anal sphincter. If a Foley catheter is in place, simply pulling on the Foley catheter can stimulate the anal sphincter contraction. The cremasteric reflex is evaluated by stroking the inner thigh and observing the scrotal sac, which should retract upward secondary to contraction of the cremasteric muscle. This function is innervated by T12 and L1. Finally, the anal wink, innervated by S2, S3, and S4, is elicited by stimulating the skin about the anal sphincter and eliciting a contraction.
The presence of spinal shock causes the absence of all reflexes and typically lasts up to 24 h after the injury. The bulbocavernosus reflex is the reflex that returns first (see Table 5–2), thus marking the end of spinal shock. This point has prognostic importance because recovery from a complete neurologic deficit that is still present at the end of spinal shock is extremely unlikely. A complete neurologic examination should be repeated over time as the patient is manipulated and treated.
The ability to interpret the results of a patient's neurologic examination appropriately depends on a thorough knowledge of the anatomy of the spinal cord and peripheral nerves.
Peripheral nerves are a combination of afferent fibers, which carry information from the periphery to the central nervous system, and efferent fibers, which carry information away from the central nervous system. As the peripheral nerve approaches the spinal cord, it becomes known as the spinal nerve. Proximal to the spinal cord, the fiber splits, with the afferent fibers becoming the dorsal root or sensory root and the efferent fibers becoming the ventral root. The afferent fibers are often regrouped in various plexuses that are located between the spinal cord and the periphery. This regrouping takes place before the fibers enter the dorsal root, therefore leading to significant overlap between the dorsal root and the respective dermatomes. The implications of this anatomic fact should be kept in mind by the clinician when performing a sensory examination. For example, a sectioned peripheral nerve is demonstrated by a highly specific sensory loss in that particular dermatome, whereas the clinical findings are more variable for a sectioned dorsal root.
The spinal cord is a caudal continuation of the brain, extending in an organized fashion from the foramen magnum at the base of the skull down to the proximal lumbar spine. The spinal cord has three primary functions: It provides a relay point for sensory information; it serves as a conduit for ascending sensory information and descending motor information; and it mediates body and limb movements because it contains both interneurons and motor neurons. Headed from caudal to rostral, the spinal cord is highly organized with a central butterfly-shaped area of gray matter and surrounding white matter.
The overall diameter of the spinal cord varies as a relative percentage of the spinal canal. The cord fills approximately 35% of the canal at the level of the atlas but increases to approximately 50% of the canal in the lower cervical spine. This variation results from the relative increasing and decreasing size of the spinal gray matter and spinal white matter. As the spinal roots become larger, as occurs at the base of the cervical spine, the size of the gray matter increases relative to the white matter, whereas the size of the white matter decreases linearly from cephalad to caudal.
The gray matter, so called because it appears gray on unstained cross sections, is divided into three zones: the dorsal horn, the intermediate zone, and the ventral horn. Made up predominantly of lower motor neurons, it is prominent in the cervical swellings and lumbar swellings, where axons concentrate before exiting to innervate the upper extremities and lower extremities, respectively.
The white matter derives its name from the fact that the axons in this area are myelinated, casting a white hue on unstained sections. White matter is functionally and anatomically divided into three bilaterally paired columns: the ventral columns, the lateral columns, and the dorsal columns.
The two major ascending systems that relay somatic sensory information are the dorsal columns and the anterolateral system. The ascending axon has its cell body located in the dorsal root ganglion before proceeding without synapsing through the dorsal horn at that level and then ascending along the dorsal column before synapsing at the approximate level of the medulla and crossing over to the contralateral side before proceeding to the cerebral cortex. The topography of the dorsal column is such that the sacrum and lower extremities are medial, with the trunk and cervical region being lateral. The anterolateral system carries pain and temperature sensorium. The afferent fibers have a cell body in the dorsal root ganglion and then synapse at that given level in the dorsal horn before crossing directly to the contralateral side and traveling up the spinothalamic tract.
Motor pathways originate in the cerebral cortex and travel distally to the contralateral side approximately at the level of the medulla and travel down the lateral corticospinal tract before synapsing with the lower motor neuron in the ventral horn of the gray matter. The topography of the corticospinal tract is such that the sacrum and legs lie lateral to the trunk and cervical axons. Thus, at the level of the cervical spine, the spinal cord contains both lower motor neurons traversing to the upper extremities and upper motor neurons being transmitted to the lower extremities. Therefore, injury in this area can give both upper and lower motor findings.
The anatomy of the reflex arc and especially its relationship to spinal shock should be kept in mind. The basic reflex circuitry is an afferent nerve coming from a stretch receptor through the dorsal horn of gray matter before synapsing with the lower motor neuron in the ventral horn of the gray matter, which sends a positive signal to the same muscle via an alpha motor neuron. This simple arc, however, is modulated by input from higher centers. If all descending influence is interrupted, such as would occur in a traumatic transection of the spinal cord, all reflexes are lost. This is also seen during spinal shock. If the local circuitry of the reflex arc is not disturbed, reflexes return at the end of spinal shock. The earliest reflex to return is the bulbocavernosus reflex, which typically returns within 24 hours of injury. Peripheral reflexes may take several months before they return.
RISK OF NEUROLOGIC DAMAGE
As mentioned earlier, the spinal cord varies in its diameter from cephalad to caudad. In the upper cervical spine, it occupies approximately a third of the spinal canal. In the lower cervical spine, it occupies approximately half of the canal. As inferred from this anatomy, the risk of neurologic damage from injury is greater in the lower cervical spine.
Cord compromise extends from two causes: mechanical destruction resulting directly from the trauma and vascular insufficiency. With vascular insufficiency, hypoxia and edema follow and result in further tissue damage. By approximately 6 hours after the trauma, axonal transport ends, and by 24 hours, cord necrosis begins.
CLASSIFICATION OF NEUROLOGIC STATUS
Approximately 60% of injuries to the cervical spine result in no neurologic sequelae. In most of these cases, the injuries are in the upper cervical spine, where the ratio of the spinal cord to the spinal canal is smaller. It is obviously critical to identify unstable injuries of the cervical spine in the intact patient because the evolution of neurologic deficits is both potentially catastrophic and preventable.
Nerve Root Injuries
Eight cervical nerve roots correspond to the seven cervical vertebral bodies. Each of the first seven nerve roots exits above its respective body (the C1 nerve exiting above the C1 vertebral body, the C2 nerve exiting above the C2 body, and so forth), whereas the C8 nerve root exits through the foramen between the C7 and T1 vertebral bodies. Nerve root injuries can happen either in isolation or in conjunction with more severe spinal cord injuries. Injury to the nerve root alone may result from a compression or fracture of the lateral bone mass and thus impingement on the neural foramen. The clinical findings of a root injury would be those of a lower motor neuron lesion. If the nerve root is still intact and the ongoing pressure to the root is removed, the prognosis for recovery of nerve root function is good.
Incomplete versus Complete Neurologic Injury
In the acute setting, any evidence of neurologic function distal to the level of injury is significant and defines the lesion as being incomplete rather than complete. As Lucas and Ducker reported in a prospective study published in 1979, "The less the injury, the greater the recovery," and "partial lesions partially recover, whereas complete lesions do not."
According to the Frankel system, which is the most widely used system for classifying sensory and motor deficits in patients with spinal cord lesions, there are five categories of injury: (A) sensory function absent, motor function absent (complete injury); (B) sensation present, motor absent; (C) sensation present, motor active but not useful; (D) sensation present, motor active and useful; and (E) normal sensory function, normal motor function.
In the acutely injured spinal cord patient, the documentation of sacral nerve root function by testing perianal sensation, rectal tone, and flexion of the great toe is critically important. Intact sacral function may be the only sign of an at least partially functioning spinal cord. In contrast, the absence of sacral function may be the only finding on physical examination in patients with an injury to the conus medullaris or cauda equina at the distal spinal column. Because these patients can move their lower extremities, a cursory examination might easily miss these significant deficits.
CLINICAL FEATURES OF SPINAL CORD SYNDROMES
Combining the findings on examination with knowledge of the cross-sectional anatomy of the spinal cord allows the examiner to identify specific injury patterns (Figure 5–35).
Central Cord Syndrome
The most common of the incomplete cord syndromes is the central cord syndrome, which occurs most frequently in elderly (more than 65 years) people with underlying degenerative spondylosis but can also be found in younger people who have had a severe hyperextension injury with or without evidence of a fracture. Central cord syndrome is defined by the American Spinal Injury Association (ASIA) as a clinical presentation characterized by "dissociation in degree of motor weakness with lower limbs stronger than upper limbs and sacral sensory sparing." The syndrome typically occurs following a hyperextension injury and is thought to be caused by an expanding hematoma or edema forming in the central aspect of the spinal cord. Central cord syndrome can be quite variable in presentation and in recovery. A mild presentation may consist of a slight burning sensation in the upper extremities, whereas a severe central cord syndrome includes motor impairment in both the upper and lower extremities, bladder dysfunction, and a variable sensory deficit below the level of injury. The pattern of clinical presentation is directly related to the cross-sectional anatomy of the spinal cord. Because the lower extremity and sacral tracts of the spinothalamic and corticospinal tracts are lateral, these areas are often spared in central cord syndrome. In cases in which they are involved, they are the areas whose function returns first. The upper extremity deficit is caused by a lesion in the gray matter, and the damage here is largely irreversible.
From 50% to 75% of patients with central cord lesions show some neurologic improvement, but the amount of improvement varies considerably among patients. The usual order in which motor function recovery occurs is as follows: return of lower extremity strength, return of bladder function, return of upper extremity strength, and return of intrinsic function of the hand.
Anterior Cord Syndrome
The patient with an anterior cord syndrome typically presents with immediate paralysis and loss of pain and temperature sensation. Both the spinothalamic and corticospinal tracts are located in the anterior aspect of the spinal cord and therefore involved. With the dorsal columns preserved, the patient still has intact proprioception and vibratory sense as well as intact sensation to deep pressure. This clinical presentation is the most common in the younger (less than 35 years) trauma victim. The mechanism of injury is typically a flexion injury to the cervical spine. It is usually associated with an identifiable lesion of the cervical spine, most commonly a vertebral body burst fracture or a herniated disk. Return of useful motor function is reported in only 10–16% of patients with anterior cord syndrome. The prognosis is slightly improved, however, if evidence of spinothalamic tract function is present early.
Patients with this syndrome have a motor weakness on the ipsilateral side of the lesion and a sensory deficit on the contralateral side caused by a functional hemisection of the spinal cord. For example, a cervical lesion on the right side of the spinal cord disrupts the ipsilateral corticospinal tract, which is the tract that carries motor function to the right side of the body distal to the level of the lesion. The right spinothalamic tract is also disrupted. This tract carries pain and temperature fibers from the contralateral side of the body distal to the level of injury. Position sense and vibratory sense, which are carried in the posterior column, have not yet crossed the midline; therefore, these sensory functions are disrupted on the ipsilateral side of the injury.
Brown-Séquard syndrome may result from a closed rotational injury such as a fracture-dislocation or may result from a penetrating trauma such as a stab wound. The prognosis in cases resulting from a closed injury is quite favorable, with 90% of patients regaining function of the bowel and bladder as well as the ability to walk.
Posterior Cord Syndrome
The posterior cord syndrome is the least common of the incomplete syndromes and typically a result of an extension type injury. Its clinical presentation is one of loss of position and vibratory sense below the level of injury secondary to disruption of the dorsal columns. With these deficits as isolated findings, the prognosis for recovery of ambulation and function of the bowel and bladder is excellent.
Complete Spinal Cord Injury
A complete neurologic deficit is characterized by a total absence of sensation and voluntary motor function caudal to the level of spinal cord injury in the absence of spinal shock. Initial evaluation must rule out any evidence of sacral sparing and the presence of a bulbocavernosus reflex. In the absence of sacral sparing and with the return of the bulbocavernosus reflex, which typically occurs within 24 hours, the spinal cord injury is termed complete and there is virtually no likelihood of functional spinal cord recovery. Affected patients may gain some root function about the level of the injury—a phenomenon called root escape because this damage to nerve roots is a peripheral nerve injury. Although the presence of root escape should not be taken as a potential return of spinal cord function, it can significantly improve the patient's rehabilitation efforts because vital function of the upper extremities may be regained.
A lateral radiograph of the cervical spine may be the only screening tool obtained upon initial radiographic evaluation of the multiple-trauma patient. This radiograph must be carefully reviewed. Should a patient present with a complete neurologic injury or a densely affected incomplete neurologic injury indicating a traumatically malaligned cervical spine, closed reduction of the cervical spine should be urgently attempted with axial traction through Gardner-Wells tongs. Once the patient is fully evaluated and life-threatening injuries are stabilized, secondary diagnostic studies can then be undertaken. If the patient is fully alert, has full pain-free rotational range of motion, no palpable tenderness, and no other injuries, the cervical spine can be cleared on clinical grounds.
Subsequent Plain Radiographs
Full radiographic evaluation of the cervical spine with plain radiographs includes lateral, AP, open-mouth (odontoid), right oblique, and left oblique views. The lateral radiograph, if adequate, visualized approximately 85% of significant cervical spine injuries. It must display the base of the skull with all seven cervical vertebrae, as well as the proximal half of the T1 vertebral body. If the C7-T1 junction is not visualized, a repeat radiograph should be done with axial traction on the upper extremities caudally to attempt to visualize the C7-T1 junction. If this is unsuccessful, a swimmer's view, which is a transthoracic lateral with the patient's arm fully abducted, should be taken. If this plain radiograph is not satisfactory and if suspicion of injury is still high, a CT scan must be obtained.
When evaluating a lateral cervical spine radiograph, the clinician should first evaluate the bony anatomy. Four lines or curves should be kept in mind (Figure 5–36). The anterior spinal line and the posterior spinal line are imaginary lines drawn from the anterior cortex and posterior cortex, respectively, of the cervical vertebral body from C2 all the way down to T1. The spinal laminar curve is an imaginary line drawn from the posterior aspect of the foramen magnum connecting the anterior cortex of each successive spinous process. These three lines (labeled A, B, and C in Figure 5–36) should have a gentle, continuous lordotic curve with no areas of acute angulation. The fourth line (labeled D in Figure 5–36) is known as the basilar line of Wackenheim, and it is drawn along the posterior surface of the clivus and should thus be tangent to the posterior cortex of the tip of the odontoid process. After the clinician examines the radiograph in terms of these four lines or curves, he or she should look at the individual vertebral bodies to see if there is loss of height of any of them or if a rotational deformity is present with alterations in the alignment of the facets.
The evaluation of soft tissues can also prove valuable diagnostically. Prevertebral soft tissues have an upper limit of normal width beyond which a prevertebral hematoma indicative of vertebral injury can be suspected. The upper ends of normal are 11 mm at C1, 6 mm at C2, 7 mm at C3, and 8 mm at C4. The measurements below C4 become more variable and therefore less reliable clinically.
The AP view of the cervical spine is at first a confusing projection to those who are unfamiliar with cervical anatomy, yet careful attention to bony detail in the AP view can be of significant diagnostic aid in picking up subtle injuries. The bony and soft-tissue anatomy seen on the AP projection should be symmetric. The spinous processes should be equally spaced because a single level of increased intraspinous process distance suggests posterior instability. Abrupt malalignment of the spinous processes suggests a rotatory injury such as a unilateral facet dislocation. After checking for these problems, the clinician should inspect the lateral masses. The facet joints are typically angled away from the vertical and therefore not clearly seen on the AP projection. If, however, the facet joint can be seen at a particular level, this is indicative of a fracture through the lateral masses and a rotational malalignment of the facet.
The open-mouth (odontoid) view is the projection most useful for looking at C1-C2 anatomy. It permits visualization of both the dens in the AP plane, and the lateral masses of C1 on C2.
The right and left oblique views can be taken of the cervical spine with the patient in the supine position. These views are useful as confirmatory studies in ruling in or out lateral mass injuries.
Two techniques are used in obtaining cervical stress radiographs. The first is to apply axial distraction to the cervical spine through a halo or traction device and obtain a lateral radiograph. This technique should be carefully performed in the presence of a physician and only after gross instabilities of the cervical spine are ruled out. Serial lateral radiographs are taken as weight is sequentially added, reaching an amount equivalent to approximately a third of body weight or 30 kg, depending on the level of suspected injury. Occult instability can be inferred by noting an interspace angulation of at least 11 degrees or an interspace separation of at least 1.7 mm (Figure 5–37).
The second technique, which should only be performed in a fully alert and cooperative patient, is used to obtain flexion-extension lateral radiographs that are helpful in the diagnosis of late instability. The technique is to have the patient flex the head forward as far as possible while a lateral radiograph is taken and then to have the patient put the head in full extension while another radiograph is taken. Findings presumptive of instability are facet subluxation, forward subluxation of 3.5 cm of one vertebral body on the next, and interbody angulation of greater than 11 degrees.
CT scanning is the most useful means for definitive delineation of bony fracture anatomy. Its advantages are its ready availability and its ability to be performed with a minimal amount of patient manipulation. CT scans provide excellent axial detail, and if the sections are taken with close enough cuts, the computer can reconstruct images in sagittal, coronal, or oblique planes. CT scans can now even be reformatted into a three-dimensional construct for excellent visualization of the bony anatomy.
MAGNETIC RESONANCE IMAGING
MRI is the most effective way to evaluate the soft-tissue component of cervical trauma. The major advantage of MRI is that it can visualize occult disk herniation, hematoma, or edema about the spinal cord, as well as ligamentous injury. Current disadvantages are that MRI is disrupted by metallic objects, so these should be removed from the area of examination, and it also requires a prolonged amount of time to perform, therefore making close monitoring of the acutely ill patient difficult.
Diagnostic Checklist of Spinal Instability
The concept of spinal stability is central to the understanding and treatment of cervical spine injuries. In a broad sense, patients with injuries that are deemed unstable require surgical intervention, whereas those deemed to have stable injury patterns can be treated nonoperatively. Spinal injuries, however, are not readily divided into unstable and stable injuries, and in actuality they fall along a spectrum of spinal instability.
White and Panjabi's diagnostic checklist of spinal instability (Table 5–3) has nine categories, each of which is assigned a point value. If a total of 5 points is present in a given patient, the injury is deemed unstable.
Holdsworth's two-column theory of spine stability, as well as Denis's three-column theory, proposed for application to the thoracolumbar spine, are also applied to the cervical spine in an attempt to better predict stability in the neck.
General Principles of Managing Acute Injuries of the Cervical Spine
Management of acute cervical spine injury is predicated on two principles: protection of the uninjured spinal cord and prevention of further damage to the injured spinal cord. This is accomplished by following spine precaution principles from the very onset of medical care, starting at the accident scene. The cervical spine should be considered injured until proven otherwise and securely immobilized before the patient is transported to a medical center. The equipment for initial immobilization should not be removed until the definitive means of immobilization can be put in place or the cervical spine is cleared of injury. Use of a spinal board, with the patient's head taped to the board and held between two sandbags, is the most secure form of immobilization readily available in the field. This technique can be supplemented by a Philadelphia collar. When the medical center is reached, if a definitive cervical spine injury is identified and deemed unstable, skeletal traction for immobilization, reduction, or both may be applied. Gardner-Wells traction is easily applied and adequate for axial traction. Halo traction affords the added advantage of four-point fixation and thus controlled traction in three planes. Halo traction can also be easily converted at a later time to halo-vest immobilization.
Among the various agents that show potential benefits in laboratory studies of models of spinal cord injury are corticosteroids, opiate receptor antagonists (such as naloxone or thyrotropin-releasing hormone), and diuretics (such as mannitol). The National Acute Spinal Cord Injury Studies (NASCIS) II and III reported neurologic improvement with steroid treatment given within 8 hours of injury. Those treated within 3 hours did best; those treated between hours 3 and 8 only did better by extending to 48 hours of treatment. Criticism of the NASCIS studies called to question the validity of the conclusions, and many professional organizations downgraded their enthusiasm for the use of methylprednisolone in the patient with the acutely injured spinal cord. However, many hospitals still use the protocol in blunt trauma cord injuries if the medicine can be administered within 3 hours of the injury. The recommended dosage of methylprednisolone in an acute setting is 30 mg/kg given as a bolus and followed by 5.4 mg/kg/h for 24 hours. However, some thought should be given to its use because, for example, the Congress of Neurological Surgeons stated that steroid therapy "should only be undertaken with the knowledge that the evidence suggesting harmful side effects is more consistent than any suggestion of clinical benefit."
INJURIES OF THE UPPER CERVICAL SPINE
With the exception of occipitoatlantal dissociation, traumatic injuries to the upper cervical spine are less frequently associated with significant neurologic injury than are traumatic injuries to the lower cervical spine. This is secondary to the fact that the spinal cord occupies only a third of the upper spinal canal versus a half of the lower spinal canal.
Occipitoatlantal dissociation is a disruption of the cranial vertebral junction, and it implies a subluxation or complete dislocation of the occipitoatlantal facets. This injury is typically fatal, yet the clinician must be aware of it because unrecognized occipitoatlantal dissociation may have catastrophic results. The mechanism of dissociation is poorly understood, but it most likely results from either a severe flexion or distraction type of injury. Anterior translation of the skull on the vertebral column is a common presentation and most likely a hyperflexion injury. Bucholz, however, presented the pathologic anatomic findings of fatal occipitoatlantal dissociation and proposed a mechanism of hyperextension with resultant distractive force applied across the craniovertebral junction.
When the dissociation is a frank dislocation, the findings are clear on a lateral radiograph. When the dissociation is a subluxation, however, findings may be more subtle. In normal individuals, the distance between the tip of the dens and the basion (the anterior aspect of the foramen magnum) should be no greater than 1.0 cm, and the previously described Wackenheim line should run from the base of the basion tangentially to the tip of the dens. If the dens penetrates this line, anterior translation of the cranium is implied. Calculation of the Powers ratio can also be helpful in securing the diagnosis. Powers and his colleagues described a ratio of two lines (Figure 5–38), the first of which runs from the tip of the basion to the midpoint of the posterior lamina of the atlas (line BC) and the second of which runs from the anterior arch of C1 to the opisthion (line AO). When the ratio of BC to AO is greater than 1:1, anterior occipitoatlantal dissociation is present. Other radiographic signs include marked soft-tissue swelling and the presence of avulsion fractures at the occipitovertebral junction.
Early recognition and surgical stabilization are the mainstays of treatment in cases of occipitoatlantal dissociation.
Fractures of Vertebra C1 (Atlas Fractures)
The mechanism of injury in the fracture of the atlas is most typically axial compression with or without extension force, and the anatomic findings of the fracture are indicative of the specifics of the force and the position of the head at the time of impact. In 1920, Jefferson presented his classic description of the four-part fracture of the atlas following an axial injury. This fracture is a burst type that occurs secondary to the occipital condyles being driven into the interior portions of the ring of the atlas and driving the lateral masses outward, resulting in a two-part fracture of the anterior ring of the atlas as well as a two-part fracture of the posterior ring. More common than the classic four-part atlas fracture, however, are the two-part and three-part fractures. Isolated anterior arch fractures are the least common, and they are typically associated with fractures of the dens, whereas the more common posterior arch fracture is typically the result of a hyperextension injury.
A fracture of the atlas is typically diagnosed on plain radiographs. Findings may be subtle on the lateral cervical spine radiograph. The open-mouth (odontoid) view may show asymmetry of the lateral masses of C1 on C2 with overhang (Figure 5–39). A bilateral overhang totaling more than 6.9 mm is presumptive evidence of a disruption to the transverse ligament and suggests potential late instability. Presumptive evidence for transverse ligament disruption can also be seen on the lateral radiograph if the ADI is greater than 4 mm.
The treatment for fractures of the atlas as isolated injuries is typically nonoperative (Figure 5–40). If there are signs of transverse ligament disruption, halo traction is indicated with later transfer to halo-vest immobilization for a total of 3–4 months. Immediate halo-vest application is indicated in cases involving a moderately displaced fracture with lateral mass overhang up to 5 mm, although collar immobilization is preferred in cases involving a minimally displaced fracture of the atlas. At completion of bony union, flexion-extension views should be obtained to rule out any evidence of late instability. If late instability is present and the bony elements were allowed to heal, a limited C1-C2 fusion can address the instability. If a nonunion is present or if the posterior arch remains disrupted, an occiput to C2 fusion is necessary to control the late instability.
Dislocations & Subluxations of Vertebrae C1 & C2
ATLANTOAXIAL ROTATORY SUBLUXATION
Atlantoaxial rotatory subluxation is most common in children and may be associated with minimal trauma or even occur spontaneously. Although some patients are asymptomatic, others present with neck pain or torticollis (a position in which the head is tilted toward one side and rotated toward the other). Inasmuch as the mechanism of injury is often unclear, the propensity for the C1-C2 location is based on anatomic factors. In approximately 50% of cases, cervical spine rotation occurs at the C1-C2 junction, where the facet joints are more horizontal and less inherently stable in rotation.
The diagnosis of atlantoaxial rotatory subluxation is typically suspected on the basis of radiographs taken in several views. The odontoid view may show displacement of the lateral masses with respect to the dens; a lateral view may show an increased ADI; and the AP view may show a lateral shift of the spinous process of C1 on C2. CT scanning can be used to confirm the diagnosis, and a dynamic CT scan with full attempted right and left rotation can demonstrate a fixed deformity.
There are four types of atlantoaxial rotatory subluxations. In type I, the ADI is less than 3 mm, which suggests the transverse ligament is still intact. In type II, the interval is 3–5 mm, which suggests the transverse ligament is not structurally intact. In type III, the interval exceeds 5 mm, which is indicative of disruption of the transverse ligament as well as secondary stabilization of the alar ligament. In type IV, there is a complete posterior dislocation of the atlas on the axis, a finding typically associated with a hypoplastic odontoid process such as that seen in several forms of mucopolysaccharidosis (eg, the Morquio syndrome).
Treatment of atlantoaxial subluxation is typically conservative, consisting of traction followed by immobilization. Approximately 90% of patients respond to this treatment regimen. There is a high incidence of recurrence, however. For patients who do not respond to conservative measures and for patients with recurrent problems, C1-C2 arthrodesis may be required to control the deformity.
DISRUPTION OF THE TRANSVERSE LIGAMENT
The transverse ligament and secondarily the alar ligament are the main constraints to anterior displacement of C1 on C2. It was previously presumed that because anterior subluxation of C1 on C2 typically involves a fracture through the dens, the transverse ligament is in fact stronger than the bony elements of the dens. Fielding and his colleagues, however, showed that experimentally this was not the case, yet clinically the higher association of anterior dislocation of dens fractures still holds true.
The mechanism of disruption is typically a flexion injury, and the diagnosis is made on lateral radiographs. The ADI should not exceed 3 mm in the adult. If the interval is 4 mm or larger and the dens is intact, a rupture of the transverse ligament is presumed.
High-resolution CT scan can be used to categorize this injury into two types. Type 1 is a disruption in the substance of the transverse ligament, whereas type 2 involves an avulsion fracture of the insertion of the transverse ligament on the lateral mass of C1. Type 1 injuries predictably fail conservative treatment and should be managed with a C1-C2 arthrodesis. A trial of nonoperative care in type 2 injuries using a rigid cervical orthosis may be a reasonable alternative. A 74% success rate can be anticipated, with surgery reserved for patients who fail nonoperative care, showing persistent instability after 12 weeks in mobilization.
FRACTURE OF THE ODONTOID PROCESS
Fracture of the odontoid process is typically associated with high-velocity trauma, and the mechanism of injury is flexion in most cases. Depending on the fracture pattern, extension may be the predominant force in a smaller subset of cases. Associated injuries, particularly fractures of the ring of the atlas, should be ruled out. Neurologic involvement is relatively rare with odontoid fractures. In a study of 60 patients with acute fractures of the odontoid process, Anderson and D'Alonzo reported that 15 had some neurologic deficit on presentation, but only 5 of the 15 had major neurologic involvement, and only 2 of this group of 5 remained quadriparetic at follow-up.
Odontoid fractures may be suspected on the basis of clinical presentation and confirmed on plain radiographs, although spasm and overlying shadows can obscure the diagnosis. CT scan with sagittal and coronal reconstruction is the most sensitive study to diagnose these injuries. CT scan with axial sectioning alone may miss the horizontal fracture line typical of these injuries; thus, the reconstructions are necessary.
Both the risk of nonunion with delayed instability and the method of treating odontoid fracture depends on the classification of the fracture. Reported rates of nonunion range from 20% to 63%. According to the classification system proposed in 1974 by Anderson and D'Alonzo, there are three types of fracture of the odontoid process (Figure 5–41).
Type I is a fracture through the tip of the odontoid process. In this configuration, the blood supply is maintained through the base of the odontoid process and through the attachment of the alar transverse ligaments. The mechanical stability of this fracture pattern is left intact. Symptomatic care and immobilization are the treatment of choice.
Type II, the most common type, is a fracture through the base of the odontoid process at its junction with the body of the axis. In this configuration, soft-tissue attachments to the fracture fragment cause distraction at the fracture site. Because the amount of cancellous bone available for opposition is limited, a high nonunion rate is expected, particularly if displacement is significant or the patient is older (more than 60 years). In this case, primary surgical treatment may be indicated. Anterior screw fixation of the odontoid process is now the treatment of choice for most type 2 odontoid fractures. Although it is technically demanding, it does allow for the maintenance of motion at C1-C2 (Figure 5–42).
Type III is a fracture through the body of the axis. The blood supply is maintained through soft-tissue attachments, and abundant cancellous bone opposition at the fracture site facilitates a high rate of union. The treatment, therefore, is conservative, consisting of halo traction or halo-vest immobilization until bony union occurs.
HANGMAN'S FRACTURE (TRAUMATIC SPONDYLOLISTHESIS OF VERTEBRA C2)
Hangman's fracture occurs when a fracture line passes through the neural arch of the axis. The anatomy of the axis is such that the superior facets are anterior and the inferior facets are posterior, thus concentrating stress through the neural arch. Because of the high ratio of spinal canal size to spinal cord size at this level, neurologic damage associated with hangman's fracture should be unusual. However, in his postmortem studies, Bucholz reported that traumatic spondylolisthesis was second only to occipitoatlantal dislocations in cervical injuries leading to fatalities.
According to the scheme proposed by Levine and Rhyne, hangman's fractures can be classified on the basis of anatomic factors and the presumed mechanism of injury. Treatment depends on the type of fracture. Imaging studies in a patient with hangman's fracture are shown in Figure 5–43.
Type I is typically caused by hyperextension with or without additional axial load. There is no angulation of the deformity, and the fracture fragments are separated by less than 3 mm. Treatment should consist of immobilization in a cervical collar or halo vest until union occurs, which is typically 12 weeks.
Type II is thought to be caused by hyperextension and axial load with a secondary flexion component leading to displacement of the fracture. Reduction of the anterior angulation in this type of fracture is necessary and typically obtained by traction therapy and then followed by placement of a halo vest until union occurs. An atypical type II hangman's fracture is described. This fracture occurs through the posterior aspect of the vertebral body, potentially resulting in cord compromise as the anterior aspect of the vertebral body flexes forward. A higher likelihood of neurologic injury with this atypical pattern is seen, and halo-vest immobilization is recommended.
Type IIA has the same fracture pattern as type II but with a component of distraction that also occurred at the time of injury and led to disruption of the C2-C3 disk space, rendering this injury inherently unstable. Traction should be avoided in cases of type IIA fracture because it exacerbates the injury. Treatment should consist of immediate halo-vest application, with the patient's head positioned in slight extension to afford a reduction.
Type III includes a fracture through the neural arch, a facet dislocation, and a disruption of the C2-C3 disk space that renders the injury highly unstable. Treatment generally consists of early closed reduction of the facet dislocation and application of a halo vest to maintain the reduction. If the reduction cannot be obtained in a closed fashion or cannot be maintained conservatively, treatment with open reduction of the dislocation and anterior or posterior fusion is indicated.
INJURIES OF THE LOWER CERVICAL SPINE
As stated earlier, fractures and dislocations of the lower cervical spine have a greater frequency of catastrophic neurologic involvement because of the decreased ratio of spinal canal to spinal cord in the lower levels. Treatment of affected patients again relies on early recognition of the injury, recognition of inherent stability or instability of the injury pattern, and institution of appropriate definitive care.
In 1982, Allen and colleagues developed a classification system for closed indirect fractures and dislocations of the lower cervical spine. After reviewing numerous cases previously described by other authors as well as 165 of their own cases, they grouped the injuries into six categories, based on the position of the cervical spine at the time of impact and on the dominant mode of failure. The six categories were compressive flexion, vertical compression, distractive flexion, compressive extension, distractive extension, and lateral flexion. Of these, the distractive flexion injuries were the most common, followed by the compressive extension injuries and the compressive flexion injuries. Some of the categories were further divided into stages, as described next.
Compressive Flexion Injury
There are five stages of compressive flexion injuries, which are labeled compression flexion stage (CFS) I through V (Figure 5–44). CFS I shows a slight blunting and rounding to the anterior superior vertebral margin, without any evidence of posterior ligamentous damage. CFS II shows some additional loss of height of the anterior vertebral body, again sparing the posterior elements. CFS III has an additional fracture line passing from the anterior surface of the vertebral body through to the inferior subchondral plate, with minimal displacement. CFS IV has less than 3 mm of displacement of the inferior posterior vertebral fragment into the neural canal. CFS V has severe displacement of the inferior posterior fragment into the canal, with widening of the spinous processes posteriorly, indicative of three-column disruption.
Within the compressive flexion category are two types of fractures, more commonly referred to as the compression fracture and the teardrop fracture. Most compression fractures without disruption of the posterior elements are thought to be stable, so no surgical intervention is required. The more severe compression fracture injuries, however, can result in displacement of bone into the spinal canal, and if a neurologic injury is present, these require anterior decompression and stabilization. All patients should be carefully checked with flexion-extension views at the completion of their treatment to rule out any evidence of late instability.
Vertical Compression Injury
Vertical compression spinal (VCS) injuries occur secondary to axial loading and are divided into three stages. VCS I consists of an endplate central fracture with no evidence of ligamentous failure. VCS II is a fracture of both vertebral endplates, again with only minimal displacement. VCS III is the more commonly termed burst fracture with a spectrum of fragmentation of the vertebral body, with or without posterior element disruption.
The treatment for VCS injuries is typically nonoperative. Traction is applied to obtain and maintain alignment, and bony union is generally complete after 3 months of halo-vest immobilization. Flexion-extension views should be obtained at the completion of healing because a posterior ligamentous injury can result in late instability.
Distractive Flexion Injury
The category of distractive flexion spinal (DFS) injury was the most common injury category reported by Allen and colleagues, and it includes both unilateral and bilateral facet subluxation and dislocation. There are four stages of DFS injury. DFS I, termed a flexion sprain, is characterized by subluxation of the facet joint, with possible interspinous process widening. This injury has subtle radiographic findings and may easily be missed during initial evaluation and therefore result in late symptomatic instability (Figure 5–45). DFS II is a unilateral facet dislocation, the diagnosis of which can be confirmed on plain radiographs. The lateral radiograph would reveal an anterior subluxation of one vertebra of approximately 25% of vertebral body width at the affected level. The facet itself may be perched or fully dislocated. DFS III is a bilateral facet dislocation with approximately 50% anterior dislocation at the affected level. DFS IV, which is also termed a floating vertebra, is a bilateral facet dislocation with displacement of a full vertebral width.
Treatment of DFS injuries depends on the severity of the injury. Achievement of anatomic alignment and spinal stability yields the best results. Patients with unilateral facet dislocation should be treated with closed reduction in the acute phase, followed by immobilization. If closed reduction is not possible, open reduction and fusion are indicated (Figure 5–46). Bilateral facet dislocations are associated with a higher incidence of both neurologic injury and instability. Treatment consisting of closed reduction and immobilization is feasible, but because it results in a high percentage of late instability, which eventually requires posterior fusion, the use of early posterior fusion is indicated.
Another fracture pattern that should be included in the discussion on flexion injuries is the clay shoveler's fracture, which is a fracture of the spinous process, typically at level C6, C7, or T1. This is an avulsion injury that generally occurs in flexion by the counteractive forces of the muscular attachments. As an isolated injury, it is considered stable and usually treated nonoperatively.
Compressive Extension Injury
The category of compressive extension (CES) injury was the second most common injury category reported by Allen and colleagues. It is divided into five stages. CES I is a fracture of the vertebral arch unilaterally, with or without displacement, and CES II is a bilateral fracture. CES III and CES IV were not encountered in the series reported by Allen and colleagues but are theoretic interpolations between CES II and CES V. CES III is a bilateral fracture of the vertebral arch articular processes, lamina, or pedicle without vertebral displacement, whereas CES IV is the same fracture pattern but with moderate vertebral body displacement. Three patients in the Allen series had CES V injuries, which were bilateral vertebral arch fractures with 100% anterior displacement.
Treatment of CES injuries is related to the three-column theory. Stabilization with a posterior, anterior, or combined approach is indicated if there is significant disruption of the middle column or of two of the three columns.
Distractive Extension Injury
Distractive extension (DES) injuries are typically soft-tissue lesions and divided into two stages. DES I is a disruption of the anterior ligamentous complex or, rarely, a nondisplaced fracture of the vertebral body. Radiographs may appear entirely normal. One clue to the diagnosis is widening of the disk space, which is sometimes present. DES II is a disruption of the posterior soft-tissue complex, which can allow posterior displacement of the upper vertebral body into the spinal canal. This lesion is often reduced at the time of lateral radiographs and may show only subtle or no changes on routine radiographs. When neurologic involvement is present, it is most commonly a central cord syndrome, and provided that no coexisting compression lesions are present, some neurologic recovery is expected.
The DES injury is usually stable and does not require surgical intervention. Late flexion-extension views, however, are indicated to rule out any evidence of late instability.
Lateral Flexion Injury
Allen and colleagues included the injuries of five patients in the category of lateral flexion (LFS) injury. This category is further divided into two stages. LFS I is an asymmetric compression fracture of the vertebral body and ipsilateral posterior arch, with no displacement in the coronal plane. LFS II has a similar fracture pattern but with displacement in the coronal plane, which suggests ligamentous disruption on the tension side of the injury. This mechanism can lead to brachial plexus injuries of varying degrees on the distracted side.
Because of the rarity of LFS injuries, treatment protocols are not well established. Surgical stabilization should be considered if late instability is expected or if there is a neurologic deficit.
Ultimately the treating physician must decide on a treatment plan. The Allen classification, although quite useful to describe an injury, is a mechanistic system that is challenging to apply to the individual patient to assess operative indications. The decision whether to operate is based on a spectrum of spinal stability and neurologic compromise. A patient with a three-column injury, continued neurologic compression, and neurologic symptoms has a clear operative indication either through an anterior, posterior, or combined approach. A fully neurologically intact patient with a one-column injury generally does fine in a brace. Patients with injury patterns in between must be treated on a case-by-case basis.
Cervical Strains & Sprains (Whiplash Injury)
Cervical strains and sprains, which are commonly referred to as a whiplash injury when associated with motor vehicle accidents, can produce a protracted and confusing clinical picture. Pain is typically the one unifying feature, yet there may be numerous other complaints, including local tenderness, decreased range of motion, headaches that are typically occipital, blurred or double vision, dysphagia, hoarseness, jaw pain, difficulty with balance, and even vertigo. It is often difficult for the physician to correlate radiographic findings, diagnostic test results, and other objective findings with the subjective complaints of the patient. The constellation of symptoms is fairly uniform, however, and should certainly not be discounted, and many investigators propose an anatomic basis for the clinical complaints. McNabb proposed that paresthesias in the ulnar distribution may be secondary to spasm of the scalenus muscle, and certainly symptoms such as hoarseness and dysphagia can be related to retropharyngeal hematoma. The cervical zygapophysial joint and facet capsule are implicated as a source for chronic pain after whiplash injury.
Figure 5–47 presents an algorithm for management of cervical strain. Radiographs should be taken because the amount of neck trauma that the patient has sustained may be significant. Radiographic findings, however, may be subtle or entirely negative. Cervical lordosis may be reversed, indicating spasm. Subtle signs of instability may also be present, and these can be further delineated on flexion-extension views if symptoms persist. The prevertebral soft-tissue window should be within normal limits to rule out any prevertebral hematoma.
Once the stability of the spine is ensured, the care of the cervical sprain or whiplash injury should be symptomatic. Initial rest, bed rest if necessary, and soft collar immobilization are indicated, along with the use of antiinflammatory medications. Early mobilization with progressive range of motion and weaning from external supports should be encouraged, however. Frequent reassurance is often necessary because the symptoms may be long lasting.
Approximately 42% of patients have persistent symptoms beyond 1 year, with approximately a third having persistent symptoms beyond 2 years. Most patients who do improve do so within the first 2 months. Factors associated with a poor prognosis include the presence of occipital headaches, interscapular pain, or reversal of cervical lordosis. Women have a worse prognosis than men, and hyperextension injuries are thought to have a worse prognosis than hyperflexion injuries.