Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

547. Anterior Thoracic Corpectomy

Sheeraz A. Qureshi, Morgan N. Chen, and Andrew C. Hecht

DEFINITION

images Anterior thoracic approaches provide a means of decompression, stabilization, and fusion for a variety of spinal pathologies, such as deformity, trauma, infection, tumors, and disc herniations.

ANATOMY

images The thoracic vertebral bodies are heart-shaped in the anteroposterior plane.

images The thoracic pedicles are oval and are larger superoinferiorly than mediolaterally.

images The average height is 8 to 15 mm and the average width is 3 to 10 mm.

images The medial cortex is the thickest; however, there is no epidural space between the medial cortical edge and the dura.16

images The facet joints are situated more anteriorly and articulate superiorly and inferiorly with a rib. As the transition from the thoracic to lumbar spine occurs, the thoracic vertebrae begin to resemble the lumbar vertebrae and the facets change from a frontal orientation to one that is more lateral.

images Please refer to approach in Chapter SP-3 regarding spinal cord vascular considerations during anterior thoracic surgery.

PATHOGENESIS

Intervertebral Disc Herniation

images Seventy-five percent of thoracic disc herniations occur between T8 and L1. They are classified as central, centrolateral, lateral, or paramedian.

images Most herniations occur central or centrolateral and are often calcified.

images The spinal canal in the thoracic spine is relatively small.

images Neurologic consequences occur from direct anterior compression of the spinal cord from a herniated disc. There can be posterior displacement of the cord and local vascular insufficiency.

Infection

images The mechanism of spinal infections is controversial. Proposed routes of infection include hematogenous spread from other infected foci, local extension from nearby infections, and direct inoculation.

images The two proposed routes of hematogenous spread are venous and arterial.

images Advocates of venous hematogenous spread argue that organisms are carried to the spine via the plexus of Batson, similar to the mechanism of tumor metastasis.2

images Proponents of arterial hematogenous spread note that the metaphyseal bone near the anterior longitudinal ligament is an area where infections typically begin. This region has an end-arteriole network that is susceptible to bacterial seeding.19

Tumor

images Most spine tumors are of metastatic origin. The spinal column is the most frequent site of skeletal metastasis.18

images Malignant cells are carried to the spine through the valveless extradural venous plexus of Batson.2,8 A recent anatomic model suggests that malignant cells can also metastasize through the segmental arteries.20

Trauma

images The articulation of the vertebral column, ribs, and sternum makes the thoracic spine relatively stable.1

images High-energy injuries are frequently required to produce injury to the thoracic spine.

images Forces associated with injury are axial compression, flexion, lateral compression, flexion–rotation, shear, flexion– distraction, and extension.

NATURAL HISTORY

Intervertebral Disc Herniation

images Wood et al described 20 patients with asymptomatic thoracic disc protrusions followed by magnetic resonance imaging (MRI).21 All patients remained asymptomatic at an average of 26 months, and most disc herniations were smaller or unchanged on repeat MRI.

images It is unknown how often asymptomatic thoracic herniations become symptomatic.

images Brown et al reported on 55 patients with 72 thoracic disc herniations.3 Fifty-four were treated initially with conservative therapy and 15 eventually required surgery. Nine of 11 patients with lower extremity complaints went on to have surgery. Two patients had myelopathy and were treated surgically. All 55 patients ultimately returned to their previous level of activity.

images Patients with lower extremity symptoms and myelopathy are likely to require surgical intervention.

Infection

images Vertebral osteomyelitis is rare and accounts for 2% to 4% of all cases of osteomyelitis.

images Staphylococcus aureus is the most common organism, accounting for almost 50% of pyogenic infections.5

images The incidence is rising as a result of a growing immunocompromised and elderly patient population, increased intravenous drug abuse, and an increase in invasive diagnostic and therapeutic procedures.

images Before medical and surgical treatment, spinal osteomyelitis carried a mortality rate of greater than 70%.10 The advent of antibiotics and anterior spinal débridement techniques has reduced mortality to less than 15%.6,13

images Carragee reported on 72 patients were treated nonoperatively with antibiotics.6 Over 33% of them required surgical débridement. Results related to patient age and immune status.

Tumor

images Over 90% of spinal tumors are metastatic lesions with a distant primary source.

images Primary tumors from the breast, prostate, lung, kidney, and thyroid are most likely to metastasize to the vertebral column.18

images Tumors that affect the anterior elements of the spine can be benign or malignant.

images Benign primary tumors that have a predilection for the anterior elements include giant cell tumors and hemangiomas. Malignant tumors that commonly affect the anterior elements include osteosarcomas, chondrosarcomas, myelomas, and lymphomas.15

images Improved diagnostics have allowed for more accurate diagnosis and improved staging.9

images Chemotherapy and radiotherapy have improved survival and local control.14

images Treatment goals include preservation of neural function, spinal stability, margin-free tumor resection, and correction of deformity.

Trauma

images Fractures of the thoracolumbar spine are the most common spinal injuries.

images The thoracic spine configuration of vertebrae, sternum, and ribcage confers an inherent stability.1

images Injuries to this region require significant force, and unstable injuries are usually a result of high-energy injuries such as motor vehicle accidents, falls from heights, and crush injuries.

images Patients can have associated injuries such as pneumothoraces, pulmonary contusions, and vascular injuries.

images Although most thoracic injuries do not involve neurologic deficit, complete neurologic deficits are more common with thoracic spine injuries due to the small neural canal, the tenuous blood supply, and the high energy needed to cause injury.4

PATIENT HISTORY AND PHYSICAL FINDINGS

images Neurologic status is examined.

images Manual motor testing

images Pin-prick and light touch sensory examination may help to localize the cord level of injury based on dermatome.

images Babinski reflex and clonus are upper motor neuron signs.

images Reflex examination of the patellar and Achilles tendons: hyperactivity is an upper motor neuron sign.

IMAGING AND OTHER DIAGNOSTIC STUDIES

images It is often useful to obtain an MRI and a CT-myelogram preoperatively. MRI is the key radiologic study to confirm the diagnosis and localize pathology. Plain CT scans are helpful in delineating bony anatomy.

images A plain CT scan should be obtained in concert with MRI on every patient with a destructive bony process, such as tumor or infection, to preoperatively assess the degree of bony loss and determine the optimal strategy for reconstruction.

images CT-myelography may be needed if MRI scans cannot be obtained or if quality of the MRI is suboptimal due to patient movement, metal artifact from prior implants, or other factors.

images CT can detail ossification of the posterior longitudinal ligament or ligamentum flavum.

images CT-myelography can also clarify whether cord compression is primarily anterior secondary to a disc fragment, or circumferential due to stenosis.

DIFFERENTIAL DIAGNOSIS

images Spinal tumors

images Infections

images Transverse myelitis

images Ankylosing spondylitis

images Fractures

images Intercostal neuralgia

images Herpes zoster

images Cervical and lumbar herniated discs

images Disorders of thoracic and abdominal viscera

images Amyotrophic lateral sclerosis

images Multiple sclerosis

images Arteriovenous malformations

NONOPERATIVE MANAGEMENT

Intervertebral Disc Herniation

images In the absence of myelopathy, most patients can be treated conservatively.

images A conservative treatment plan should include nonsteroidal anti-inflammatories, rest, activity modification, and physical therapy focusing on trunk stabilization.3

images Other options include intercostal nerve blocks and pharmacotherapy such as narcotics, tricyclic antidepressants, serotonin-reuptake inhibitors, and certain antiepileptics.

Infection

images Vertebral infections should be treated nonoperatively with culture-specific antibiotics and spinal immobilization.

images Open or CT-guided biopsy can aid in targeting appropriate antibiotic treatment.

images Treatment frequently involves 6 weeks of parenteral antibiotics followed by a course of oral antibiotics.

images An infectious disease consultant can help guide the antibiotic regimen.

images External immobilization with an orthosis can help stabilize the spine, decrease pain, and prevent deformity.

images Bracing is particularly important in patients with greater than 50% destruction of the vertebral body since they are at greater risk for deformity.7

images Response to treatment can be followed clinically with erythrocyte sedimentation rate, C-reactive protein, and a complete blood count.

Tumor

images A multidisciplinary approach including a neuroradiologist, pathologist, oncologist, and spine surgeon is used to treat spinal tumors.

images A CT-guided biopsy can help establish a diagnosis in 76% to 93% of lesions.9,18

images Metastatic lesions that do not compromise spinal stability and without rapid neurologic progression can be managed nonoperatively.18

images Nonoperative treatment can include radiation, chemotherapy, embolization, and bracing.

images Most primary spinal tumors cannot be treated nonoperatively.

Trauma

images Most thoracic and thoracolumbar spine injuries can be effectively treated nonoperatively.

images Conservative treatment can include recumbency, bracing, and pain management for patients without neurologic deterioration and with a structurally stable injury.11,17

images Decubitus ulcers, thromboembolism, urinary tract infections, and late pain are complications reported with nonoperative treatment.12

SURGICAL MANAGEMENT

images Indications for discectom.

images Progressive myelopathy due to anterior compressive lesions

images Lower extremity weakness or paralysis

images Radicular pain refractory to conservative therapy

images Deformity correction

images Indications for corpectom.

images Fractures with anterior spinal cord compression

images Metastatic or primary thoracic tumors

images Osteomyelitis

images Sequestered disc herniations that have migrated behind the vertebral body

images Ossification of the posterior longitudinal ligament

images Indications for bone grafting and cage or allograft placement

images Infectio.

images Although somewhat counterintuitive, anterior spinal infections can be successfully managed with allograft, cage, or instrumentation reconstruction if a thorough débridement of infected tissues is performed and postoperative antibiotics are administered

images Tumor

images Trauma

images Degenerative disease

images Deformity correction (scoliosis, kyphosis)

images Indications for polymethylmethacrylate (PMMA) us.

images Anterior column reconstruction of tumors in patients with a life expectancy of less than 1 year

images Patients in whom the use of radiation or chemotherapy is anticipated

images Indications for plate fixatin

images Anterior and middle column instability

images Revision of failed posterior fusion

images Pseudarthrosis

images Indications for use of solid rod instrumentatio.

images Patient under 30 years of age

images Thoracic and thoracolumbar curves of less than 65 degrees (Cobb angle)

images Thoracic or lumbar compensatory curves that correct to less than 20 degrees with side bending

images Hypokyphosis (less than 20 degrees from T5 to T12)

images Refer to Chapter SP-3 for preoperative planning, patient positioning, and approach discussions.

TECHNIQUES

THORACIC DISCECTOMY

images  After elevating the articular ligaments of the costotransverse and costovertebral articulations, the remaining rib head is excised (TECH FIG 1).

images  The superior edge of the pedicle of the caudal vertebra is resected with a rongeur to expose the dural tube.

images  To find the disc herniation, the surgeon follows the superior edge of the pedicle to the vertebral body and disc space.

images  The disc herniation is removed using small angled curettes and pituitary rongeurs.

images  Discectomy can be facilitated by removing a small portion (1 to 2 cm) of the adjacent vertebral bodies. If the disc is extremely calcified or has migrated behind the vertebral body, it is helpful to perform hemicorpectomies of the adjacent vertebral bodies.

images  The portion of the disc that lies away from the ventral aspect of the spinal cord should be removed first. Once a cavity is created by removing this initial disc and bone, the rest of the disc can be removed into this cavity, ensuring that all forceful maneuvers are directed anteriorly away from the thecal sac.

images  We prefer to keep the posterior longitudinal ligament (PLL) intact whenever possible, as its removal often results in substantial epidural bleeding. We will pass an elevator or nerve hook through a rent in the PLL if one is present to ensure adequate decompression from pedicle to pedicle. If the PLL needs to be removed, we use bipolar cautery to cauterize the PLL and then carefully remove it with either a Kerrison or a combination of pituitary rongeur and curette.

images

TECH FIG 1  The rib head can be removed with a high-speed burr once the costotransverse and costovertebral articulations are excised.

THORACIC OR THORACOLUMBAR CORPECTOMY

images  The posterior aspect of the vertebral body is identified.

images Discectomy is performed above and below the level of the corpectomy.

images The lateral annulus is incised using a no. 10 blade to the anterior midline.

images An elevator is then used to separate the disc from the endplates.

images Discectomy is completed using curettes and rongeurs.

images  Attention is turned to the vertebrectomy. Using a 4-mm burr, the surgeon removes most of the bone from the vertebral body.

images Corpectomy is completed by removing the remaining bone with a rongeur (TECH FIG 2).

images Depending on the nature of the pathology, the PLL may need to be removed for the purposes of decompression.

images  For retropulsed fracture fragments, the fragments are first thinned using a high-speed 4-mm ball-tipped burr.

images

TECH FIG 2  Corpectomy site.

images  Then a thin, sharp curette is used to peel the fragments away from the dura and into the created trough.

images It is important to work quickly but carefully at this point as there can be a significant amount of epidural bleeding.

images  The posterior cortical fragments are removed from the contralateral (deep) side of the canal first so that the bulging dura will not obscure the rest of the fragments.

images  Decompression is adequate when the dura can be seen bulging into the corpectomy trough and the spinal canal has been decompressed throughout its complete width.

Plating

images  A flat surface is prepared for the plate by removing lateral endplate prominences and rib heads with a highspeed burr.

images  Using an awl insertion guide, a posterior bicortical thoracic bolt is placed at the cephalad and caudad fixation levels.

images  The trajectory should be parallel to the endplate and angled slightly anteriorly to avoid penetrating the canal (TECH FIG 3A).

images  If sagittal correction or interbody graft placement is needed, distraction is performed on the endplates using a lamina spreader.

images  A correct-length plate is applied over the bolts without extending into the adjacent disc spaces (TECH FIG 3B,C). Nuts are applied loosely to secure the plate to the posterior bolts.

images  Using a drill or awl, correct-length anterior screws are placed angling slightly posteriorly.

images In general, bicortical screws are preferred because the cancellous bone of the vertebral body provides relatively weak purchase, especially in patients with tumors or infections.

images

TECH FIG 3  Application of plate and screws. A. Osteophytes are removed, and a trajectory is planned parallel to the endplate and angled slightly anteriorly to avoid penetration of the canal. B. Nuts secure the posterior bolts, and screws are applied anteriorly. C. It is important for the screws to be a safe distance from the dural covering of the spinal cord.

SCREW–ROD INSTRUMENTATION

images  Use of an anterior screw–rod construct allows for correction of coronal plane deformity through fusion of fewer spinal motion segments compared with posterior instrumentation.

images  The entry position for the anterior vertebral screws is determined based on the location of the vertebral foramen, as this identifies posterior body cortex.

images  The surgeon inserts the most cephalad and caudad screws first in the midlateral vertebral body at the same distance from the posterior cortex (TECH FIG 4).

images  The screw tips should engage the far cortex of each vertebra and should be directed toward the posterolateral corner of the vertebra.

images  The rest of the screws are placed in similar fashion.

images  The rods are inserted as directed by the particular system, and alignment is corrected before tightening.

images

TECH FIG 4  Application of screw–rod instrumentation.

BONE GRAFTING AND CAGES

images  It is of utmost importance to prepare an adequate fusion bed.

images  A thorough decortication is performed.

images  Although placement of the graft on preserved bleeding subchondral endplates is preserved, creating a slot or peg hole in the adjacent vertebral bodies can help to prevent graft extrusion.

images  Before graft placement, kyphotic deformity can be corrected by distracting adjacent vertebrae.

images Extreme care must be taken to avoid injury to the adjacent endplates during distraction, especially in patients with osteoporosis or other states with compromised bone quality (tumors, infections).

images  After the graft has been anchored, compression locks the graft in position.

images  If tricortical iliac crest bone is used, we prefer to have the cortical smooth surface face the spinal canal.

images  Single-level corpectomy defects can be supported with tricortical iliac crest grafts, whereas larger defects are better stabilized with autogenous fibular strut grafts or shaft allografts.

images Depending on the size of the patient, humeral shafts often provide the best fit in the thoracic spine.

images  For cage placement, the ends of the cage can be trimmed to create the necessary cage configuration (TECH FIG 5A).

images Alternatively, stackable cages (eg, those made of PEEK) can be measured to fit the space.

images  The packed cage is implanted between the distracted adjacent endplates (TECH FIG 5B).

images  The cage is stabilized when the distraction is released.

images  Bone graft should be packed in and around the cage.

Polymethylmethacrylate

images  PMMA may be used in patients with spinal tumors who have poor life expectancy, or who are unlikely to heal anterior bone grafts due to poor bone quality or healing potential.

images

TECH FIG 5  A. Titanium mesh cages. B. Cage placement.

images  It provides immediate spinal stability and is strongest in compression.

images  The PMMA can be reinforced and anchored with Steinmann pins drilled into the adjacent vertebral bodies.

images  Bends in the Steinmann pins can prevent pin migration.

images  To increase interdigitation of the cement, multiple drill holes are placed in the adjacent vertebral bodies.

images

POSTOPERATIVE CARE

images Chest tubes remain until output is less than 150 mL over 24 hours.

COMPLICATIONS

images The exiting nerve root can be injured while removing the pedicle.

images Vascular injury

images Intercostal neuralgia

images Atelectasis

images Neurologic injury

images Wrong-level surgery

images Significant bleeding can be encountered when entering the epidural space.

REFERENCES

1.     Andriacchi TP, Schultz A, Belytschko T, et al. A model for studies of mechanical interactions between the human spine and rib cage. J Biomech 1974;7497–7507.

2.     Batson OV. The role of the vertebral veins in metastatic processes. Ann Intern Med 1942;16:38–45.

3.     Brown CW, et al. The natural history of thoracic disc herniation. Spine 1992;17:S97–S102.

4.     Burke DC, Murray DD. The management of thoracic and thoracolumbar injuries of the spine with neurological involvement. J Bone Joint Surg Br 1976;58B:72–78.

5.     Butler JS, Shelly MJ, Timlin M, et al. Nontuberculous pyogenic spinal infection in adults: a 12-year experience from a tertiary referral center. Spine 2006;31:2695–2700.

6.     Carragee EJ. Pyogenic vertebral osteomyelitis. J Bone Joint Surg Am 1997;79A:874–880.

7.     Frederickson B, Yuan H, Olans R. Management and outcomes of pyogenic vertebral osteomyelitis. Clin Orthop Relat Res 1978;131:160–167.

8.     Harada M, Shimizu A, Nakamura Y, et al. Role of the vertebral venous system in metastatic spread of cancer cells to the bone. Adv Exp Med Biol 1992;324:83–92.

9.     Lis E, Bilsky MH, Pisinski L, et al. Percutaneous CT-guided biopsy of osseous lesion of the spine in patients with known or suspected malignancy. AJNR Am J Neuroradiol 2004;25:1583–1588.

10. Makins GH, Abbott FC. On acute primary osteomyelitis of the vertebrae. Ann Surg 1896;23:510–539.

11. Mumford J, Weinstein JN, Spratt KF, et al. Thoracolumbar burst fractures: the clinical efficacy and outcome of nonoperative management. Spine 1993;18:955–970.

12. Rechtine GR II, Cahill D, Chrin AM. Treatment of thoracolumbar trauma: comparison of complications of operative versus nonoperative treatment. J Spinal Disord 1999;12:406–409.

13. Rezai AR, et al. Contemporary management of spinal osteomyelitis. Neurosurgery 1999;44:1018–1025.

14. Simmons ED, Zheng Y. Vertebral tumors: surgical versus nonsurgical treatment. Clin Orthop Relat Res 2006;443:233–247.

15. Simon MA, Springfield D. Surgery of Bone and Soft-Tissue Tumors. Philadelphia: Lippincott-Raven, 1998.

16. Vaccaro AR, et al. Placement of pedicle screws in the thoracic spine. 1. Morphometric analysis of the thoracic vertebrae, J Bone Joint Surg Am 1995;77A:1193–1199.

17. Weinstein JN, Collalto P, Lehmann TR. Long-term follow-up of nonoperatively treated thoracolumbar spine fractures. J Orthop Trauma 1987;1:152–159.

18. White AH, Kwon B, Lindskog D, et al. Metastatic disease of the spine. J Am Acad Orthop Surg 2006;14:587–598.

19. Wiley AM, Trueta J. The vascular anatomy of the spine and its relationship to pyogenic vertebral osteomyelitis. J Bone Joint Surg Br 1959;41B:796–809.

20. Willis TA. Nutrient arteries of the vertebral bodies. J Bone Joint Surg Am 1949;31A:538–540.

21. Wood KB, et al. Magnetic resonance imaging of the thoracic spine: evaluation of asymptomatic individuals. J Bone Joint Surg Am 1995;77A:1631–1638.



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