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

544. Lumbar Decompression

Bradley K. Weiner and Aristidis Zibis

DEFINITION

images Degenerative changes that are part of the aging process may lead to compression of neurologic tissues within the spinal canal or subarticular zones (with or without the foraminal zone) of the lumbar spine.

images This spinal canal stenosis may lead to neurogenic claudication or a monoradiculopathy.

ANATOMY

images The functional vertebral unit is depicted in FIGURE 1. More details are given in the anatomy section of Chapter SP-12.

images Spinal canal stenosis is best classified based on vertical extent of compression, regions of the canal involved, and severity of the involvement.

images Accurate anatomic classification facilitates preoperative planning and can minimize the risk of surgical complications such as missed pathology and iatrogenic root injury.

PATHOGENESIS

images Degenerative changes can affect the disc, the soft tissues, and the facet joints of the spinal unit.

images Annular bulging of the disc, ligamentum flavum hypertrophy and infolding, and osteophyte formation on the facet joints can contribute to neurologic compression. Occasionally, epidural lipomatosis also contributes to spinal stenosis, especially in the presence of insulin-dependent diabetes mellitus (IDDM).

images This compression occurs slowly and gradually affects the blood supply (arterial inflow and venous outflow) of traversing nerve roots and the free flow of cerebrospinal fluid within the common dural sac. When increased demands are placed, as in walking, the nutritional needs of the nerve roots cannot be met and noxious byproducts of metabolism cannot be removed, resulting in neurophysiologic malfunction characterized clinically by paresthetic and cramping symptoms in the legs.

images As in lumbar disc herniations, many patients with spinal stenosis are asymptomatic, suggesting that other factors intrinsic to nerve root function and adaptability are equally important (eg, smoking, vascular disease, diabetes).

NATURAL HISTORY

images Patients with mild to moderate symptoms and mild to moderate neurologic compression may respond to conservative care. Unless the compression increases, symptoms generally remain stable, with minimal resolution and minimal worsening.

images The more severe the symptoms and the more severe the neurologic compression, the more likely symptoms will progress, the less likely they will respond to conservative measures, and the more likely patients will seek surgical intervention.

HISTORY AND PHYSICAL FINDINGS

images Symptomatic patients with spinal canal stenosis generally present with neurogenic claudication (70%), monoradiculopathy (15%), or a combination of the two.

images Foraminal stenosis (10% to 15% of cases) is best diagnosed clinically by a severe monoradiculopathy of an exiting nerve root, and radiographically on parasagittal MRI imaging or CT sagittal reconstruction (FIG 2).

IMAGING

images As described in Chapter SP-12, MRI is the imaging study of choice for the diagnosis and anatomic classification of spinal canal stenosis.

images CT myelography is invasive and can better resolve the bony component of stenosis compared to MRI. Myelograms taken in flexion-extension may demonstrate a dynamic component to the stenosis. CT myelograms may be particularly useful in patients who have had prior surgery (where MRI may be difficult to interpret due to scarring) and in those with associated spinal deformity (eg, scoliosis).

images Plain radiographs are useful in demonstrating instability in the coronal (lateral listhesis) or sagittal (spondylolisthesis) planes that may need to be addressed with fusion in addition to decompression. Upright anteroposterior, lateral, and flexion-extension views can be obtained.

DIFFERENTIAL DIAGNOSIS

images Vascular claudication, bilateral hip osteoarthritis, peripheral neuropathy, and “pump problems” such as congestive heart failure or coronary artery disease resulting in poor peripheral vascular flow.

NONOPERATIVE MANAGEMENT

images Patients with mild or moderate claudicant symptoms or a monoradiculopathy may respond to physical therapy, nonsteroidal anti-inflammatories, and epidural or root sleeve steroid injections. While some patients may relapse into symptoms, many in this group are content to repeat these efforts or to live with their symptoms.

images Patients with significant claudication generally do not respond to nonoperative measures, or they respond only temporarily. Most will elect to undergo operative decompression. Similar to disc herniations, absolute surgical indications include a cauda equina syndrome and progressive neurologic deficits.

SURGICAL MANAGEMENT

images The evidence base is clear: decompressive laminectomy or laminotomy is the operative technique with the best-documented long-term outcomes and is the gold standard of surgery for spinal canal stenosis.

images

FIG 1  Functional vertebral unit.

Preoperative Planning

images Planning is vital and should aim to answer several questions:

images What is the patient's clinical syndrome?

images What levels are involved?

images Is the involvement “intersegmental”?

images Are the foramina involved?

images Is there associated pathology: disc herniation, synovial cyst, or degenerative spondylolisthesis or lateral listhesis?

images The answers to these questions will direct the surgical approach, with the goal being complete and safe decompression of compressed neurologic tissue while minimizing damage to tissues not directly involved in the pathologic process.

images

FIG 2  Classic foraminal stenosis due to osteophyte formation on the tip of the superior articular facet demonstrated on CT sagittal reconstruction.

Positioning

images Prone positioning on a well-padded frame is used (generally the Andrew's, Wilson, or Jackson; see techFig 4A in SP-12). The hips and knees are gently flexed to decrease lumbar lordosis and to facilitate the interlaminar approach. The abdomen is free to decrease intra-abdominal pressure and venous backflow into the canal.

images Shoulders should be gently flexed and abducted to less than 90 degrees; eyes, elbows, knees, and feet need to be well padded.

images A needle is passed between and lateral to the spinous processes at the involved level or levels and C-arm imaging used to confirm the level. The needle is removed and the level or levels are marked and labeled on the skin (see techFig 4B in SP-12).

Approach

images After initial dissection, one of two windows will be undertaken based on the location of stenosis: the interlaminar window or the intertransverse window.

images The traditional interlaminar approach of laminotomy or laminectomy is used in about 90% of cases of spinal canal stenosis requiring operative intervention.

images It is used to decompress soft and bony tissues that compress the neurologic structures within the central canal and subarticular zones throughout the lumbar spine.

images Two less invasive approaches may also be used and have outcomes similar to those seen with the more traditional approach: microdecompression via a unilateral approach and microdecompression via spinous process osteotomies.

images Both techniques afford bilateral decompression of spinal canal stenosis via a unilateral approach.

TECHNIQUES

INCISION

images The skin incision is made directly midline posteriorly and extends from the top of the most cephalad involved spinous process to the bottom of the most caudally involved spinous process (about 1.5 inches for single-level pathology).

images The subcutaneous tissues are gently mobilized and retracted to allow visualization of the dorsolumbar fascia.

Traditional Interlaminar Window for Decompression

images The dorsolumbar fascia is incised in the midline along the length of the skin incision, allowing exposure of spinous processes at each level.

images A Cobb elevator is then used to gently elevate the muscles (multifidus) from the spinous processes and laminae to the midportion of the facet joints bilaterally.

images A retractor is then placed and an intraoperative fluoroscopic image obtained to confirm the levels.

images At this point, illumination or magnification, based upon surgeon preference and experience, is gained by the use of the operative microscope or headlamp or loupes.

images A midline laminotomy is performed on the undersurface of the cephalad lamina to above the level of the insertion of the ligamentum flavum.

images The insertion point is invariably in line with the most cephalad portion of the facet joint.

images This laminotomy is then continued into the subarticular zone laterally (medial facetectomy) and then to include the superior surface of the caudal lamina (TECH FIG 1).

images This bony work allows for exposure and excision of soft and hard tissues compressing the common dural sac and nerve roots and should be enough to get the job done safely and completely while avoiding iatrogenic injury.

images The surgeon should aim to limit the medial facetectomies to less than 50% bilaterally and to preserve at least 5 mm of the lateral pars intra-articularis.

images In cases with concomitant congenital stenosis (involvement in the anatomic “third story” [see Chap. SP-12]; about 15% of cases), complete midline laminectomy may be needed because the lamina itself is part of the pathologic compressive process.

images In the absence of congenital stenosis or deformity, a decompressive procedure that spans the distance from the top to the bottom of the facet joint will adequately decompress the central portion of the canal in most cases. This is because in most cases central stenosis occurs where the disc, ligamentum flavum, and facets converge to impinge upon neural structures.

images Soft and hard compressive tissue is then excised, allowing for decompression of the common dural sac and nerve roots.

images This includes the ligamentum flavum in its entirety (in the midline—decompression of the central canal; its insertion on the undersurface of the capsule; a trumpeted decompression within the subarticular zone via medial facetectomy) and undercutting of the tip of the superior articular process and osteophytes from the facet joints.

images Generally, no retraction of the underlying dura and roots is needed since most pathology is visible and accessible posteriorly.

images Concomitant pathology will also need to be addressed if present.

images Degenerative spondylolisthesis should be treated by spinal fusion with or without instrumentation, as discussed in following chapters.

images Synovial cysts will need to be completely excised and the pseudocapsule gently peeled from the dura.

images Disc herniation should be addressed as described in Chapter SP-12.

images The process is repeated at each clinically involved level. Generally, a residual laminar bridge is maintained at each level for routine decompression for degenerative stenosis (laminotomy). Cases of congenital stenosis require midline laminectomy given the compression within the “third story.”

images The wound is then irrigated and hemostasis obtained. The use of a drain is optional, depending on the degree of oozing. The wound is then closed in three layers (fascia, subcutaneous tissue, skin in running subarticular fashion).

images

TECH FIG 1  Laminotomy or laminectomy is performed to allow access to the ligamentum flavum, which is excised in its entirety in a trumpeted fashion throughout the segment. Medial facetectomy is included to address any bony stenosis in the subarticular zones.

MICRODECOMPRESSION VIA THE INTERLAMINAR WINDOW

Unilateral Approach

images Microdecompression via a unilateral approach may be used for patients with a predominant monoradiculopathy with or without neurogenic claudication and degenerative stenosis with minimal to no spondylolisthesis.

images In other words, it is a good option in any case that may be adequately decompressed via laminotomy.

images A unilateral approach and decompression similar to that described above is undertaken on the ipsilateral side.

images The contralateral side is decompressed via excision of the inferior half of the spinous process and laminar junction, allowing exposure and excision (by working underneath the interspinous ligament) of the contralateral ligamentum flavum via progressive angulation of the microscope, progressive resection of the contralateral laminae (covering the entire area where the ligamentum inserts), and ligamentum resection in its entirety (TECH FIG 2).

images This operation is technically demanding but affords a recovery similar to that seen with microdiscectomy.

images

TECH FIG 2  Microdecompression. A unilateral approach is used and a unilateral decompression performed. The contralateral side is decompressed by angulating under the interspinous ligament in a trumpeted fashion.

Spinous Process Osteotomy Approach

images Microdecompression via spinous process osteotomies may be used as a less invasive alternative for surgeons more comfortable with the traditional approach.

images It affords the visualization of traditional midline approaches while preserving the spinous process and interspinous and supraspinous ligaments.

images A unilateral approach is used, similar to typical discectomy.

images The spinous processes are then osteotomized just posterior to their junction with the laminae.

images When the retractor is placed, the typical bilateral interlaminar window is exposed and decompression as described above is undertaken (TECH FIG 3).

images Once the retractor is removed, the spinous processes fall back into place and generally heal back to the residual laminar ring.

images

TECH FIG 3  Spinous process osteotomies. A unilateral approach is used and the spinous processes are osteotomized near their base. The spines are then retracted, allowing exposure of the “usual” interlaminar window. After decompression, the spines fall back into place and generally heal to the residual laminar bridge.

FORAMINAL DECOMPRESSION VIA THE INTERTRANSVERSE WINDOW

images Foraminal stenosis may be present with or without associated stenosis within the central canal and subarticular zone (addressed separately as above). With the exception of L5–S1, where it is accessible via an interlaminar window, it will need to be addressed via the intertransverse window.

images Adequate decompression of foraminal stenosis via an interlaminar approach requires resection of the lateral pars and results in potential instability at the level. The intertransverse window is a less morbid and easier approach to the foraminal zone and requires minimal resection of the lateral pars.

images The multifidus is taken medially and the longissimus is

taken laterally by finger dissection, allowing placement of a retractor in this intermuscular–nervous plane.

images The tip of the superior articular process and the lateral pars interarticularis are exposed with electrocautery.

images Staying within the capsule of the facet joint to protect the underlying exiting root, the surgeon excises the tip of the superior articular process entirely, affording a bony decompression of the foramen (TECH FIG 4). Concomitant soft tissue stenosis (ligamentum flavum insertion in the subarticular zone or lateral disc herniation) can then be easily addressed if present.

images Irrigation, hemostasis, and closure are performed as described above.

images

TECH FIG 4  Foraminal decompression. Excision of the tip of the superior articular process and part of the pars interarticularis via a paraspinal approach (A) affords decompression of the exiting root in the foramen (B).

images

POSTOPERATIVE CARE

images After surgery, patients are fitted with a light lumbar corset and are encouraged to walk once anesthesia has worn off and pain permits. About 25% will be ready for discharge as 23-hour observation patients. The others (older patients and those with comorbidities) are discharged once they are medically stable and can mobilize adequately.

images Once home, patients engage in a program of progressive walking, stretching, and corset use for comfort. For those progressing slowly, physical therapy may be introduced.

images If all is well, they may drive in about a week and return to light work once they feel up to it. Heavy labor should be avoided for 6 to 12 weeks to ensure proper soft tissue healing. Long-term activities are not restricted.

OUTCOMES

images In most patients, there is an 80% likelihood of an excellent or good outcome 2 years after surgery.

images Patients with significant medical comorbidities (eg, diabetes, heavy smoking, peripheral vessel disease, coronary artery disease) are less likely to do well; these comorbidities reduce the likelihood of an excellent or good result by an estimated 15% to 20%.

images Truly informed consent is recommended, as these procedures are not benign in this population.

COMPLICATIONS

images Dependent on the surgeon: wrong level, wrong side, missed pathology, iatrogenic instability, root injury, dural tear, hemorrhage, positioning (eg, eyes, ulnar nerve)

images Dependent on the operative environment and patient: wound infection, urinary retention, thrombophlebitis or pulmonary embolism

REFERENCES

1.     Herkowitz HN, Kurz LT. Degenerative lumbar spondylolisthesis with spinal canal stenosis: a prospective study comparing decompression with decompression and intertransverse process arthrodesis. J Bone Joint Surg Am 1991;73A:802–808.

2.     Johnsson KE, Rosen I, Uden A. The natural course of lumbar spinal stenosis. Clin Orthop Relat Res 1992;279:82–86.

3.     Katz JN, Lipson SJ, Chang LC, et al. 7 to 10 year outcome of decompressive surgery for degenerative lumbar spinal stenosis. Spine 1996; 21:92–98.

4.     Weinstein JN, et al. Initial results of ‘SPORT': operative and nonoperative treatment of lumbar spinal canal stenosis. Reported at the International Society for the Study of the Lumbar Spine Annual Meeting, 2006.

5.     Weiner BK, Fraser RD, Peterson M. Spinous process osteotomies to facilitate lumbar decompressive surgery. Spine 1999;24:62–66.

6.     Weiner BK, Walker M, Brower RS, et al. Microdecompression for lumbar spinal canal stenosis. Spine 1999;24:2268–2272.



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