The surgical management of complicated spinal stenosis: spondylolisthesis

THE SURGICAL MANAGEMENT OF COMPLICATED SPINAL STENOSIS: SPONDYLOLISTHESIS RAJ D. RAO, MD, and HARRY N. HERKOWITZ, MD

The principles of surgery in spinal stenosis follow a clear understanding of the pathology in the various types of stenosis. This article describes how the basic technique of one-level decompression in spinal stenosis is modified to deal with the pathology in degenerative spondylolisthesis. We have provided an explanation of the pathology in spinal stenosis with degenerative spondylolisthesis, and how modifications of the basic decompressive technique are necessary to deal with these variations in pathology. The indications and technique for a concomitant lateral spinal fusion are described. Techrdques of instrumentation are not covered in this article. KEY WORDS: spinal stenosis, spondylolisthesis surgery

Degenerative spondylolisthesis most often appears in patients in their sixth decade. Forward slippage of one vertebra on another, in the presence of an intact neural arch, makes the diagnosis evident on radiographs. Most of these patients do well with nonoperative measures. Surgery is indicated when the symptoms are predominantly in the lower extremities, nonoperative measures have failed, and there is a significant reduction in the patient's quality of life.

PATHOLOGY IN DEGENERATIVE SPONDYLOLISTHESIS Long-standing degenerative changes at the disk facet complex can eventually result in anterior or lateral vertebral slippage. This most commonly occurs at the L4-5 level, and may be accompanied by a sacralized L5 or a high-riding L4 vertebra. Sagittal narrowing of the canal results from the inferior margin of the posterior arch of L4 encroaching on the spinal canal. In addition, as the body of L4 slips forward, the L5 nerve root gets tethered and compressed in the narrowed lateral recess, between the anteriorly eroding and advancing inferior facet of L4 and the posterior superior aspect of the L5 vertebral body and the L4-5 disk 1 (Fig 1, 2). The L4 root may get compressed between the hypertrophied superior facet of L5 and the posterior inferior edge of the L4 body (Fig 1). Relief of symptoms results from adequate decompression of the narrowed thecal sac, along with decompression of the affected nerve roots at the sites of compression.

From the Department of Orthopaedic Surgery, William Beaumont Hospital, Royal Oak, MI. Address reprint requests to Harry N. Herkowitz, MD, Department of Orthopaedic Surgery, William Beaumont Hospital, 3535 W. 13 Mile Rd, Suite 604, Royal Oak, M148073. Copyright © 1997 by W.B. Saunders Company 1048-6666/97/0701-0008505.00/0

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SURGICAL TECHNIQUE FOR DECOMPRESSION We have been satisfied with our experience positioning the patient in the knee-chest position using the Andrews table. Surgical exposure of the posterior spinal elements is performed in routine fashion. After confirmation of the levels, decompression is begun by removing the inferior half to two thirds of the spinous process of L4 with a large rongeur. The superior half to two thirds of the spinous process of L5 is similarly removed with a large rongeur. The inferior half of the lamina of L4 and the superior half of the lamina of L5 are then thinned using a rongeur or large bur, to facilitate subsequent use of the Kerrison punch. The insertion of the ligamentum flavum onto the undersurface of L4 is then delineated with a small 3-0 angled curette. A Kerrison punch is then used to resect inferior laminar bone from L4 in the midline, till either epidural fat or dura are visualized. An angled Frazier elevator is then slid through this "window" distally into the plane between the dura and ligamentum flavum, and the ligamentum incised in the midline distally toward the superior edge of the L5 lamina. A curette or Kerrison punch are then used to excise the insertion of the ligamentum onto the superior edge of the L5 lamina in the midline and on either side of the midline. Residual ligamentum flavum is then excised sharply or with a small rongeur. Using a Kerrison punch, laminar bone is resected, beginning in the midline and extending on either side to the medial wall of the pedicles. Superiorly, the inferior half to two thirds of the L4 lamina is removed and inferiorly the superior half of the L5 lamina is removed. At the end of this stage of the decompression, there is a central rectangular defect in the posterior elements of the selected levels (Fig 3). The dura is clearly visible, and bleeding is controlled by thrombin-impregnated Gelfoam (Upjohn, Kalamazoo, MI) and cottonoids. Decompression of Lateral Recess

After this central decompression has been performed, the next step is the examination and appropriate decompresOperative Techniques in Orthopaedics, Vol 7, No 1 (January), 1997: pp 44-47

Root

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Fig 1. Schematic sagittal section showing pathology in degenerative spondylolisthesis. The L5 root is trapped in the lateral recess between the anteriorly eroding inferior articular process of L4 and the posterior aspect of the body of L5 and the L4-5 disc. The L4 root may get pinched between a hypertrophic superior articular process of L5 posteriorly and the posterior inferior edge of the L4 vertebral body and bulging L4-5 disc anteriorly.

sion of the lateral recesses and foraminal nerve root regions. The traversing nerve root (L5) will often be pinched in the lateral recess beneath the advancing inferior facet of L4, the hypertrophic superior facet of L5, the hypertrophic facet joint capsule, and the attachment of the ligamentum flavum onto the joint capsule. Facet joints in degenerative spondylolisthesis are often sagittally oriented, with a corresponding reduction in coronal dimension. 2 As much of the facet joint as necessary must be resected to completely decompress the nerve root. A combined bilateral total of one facet joint may be resected without compromising stability. 3 An angled Frazier elevator is passed from medial to lateral, along the L5 nerve root into the neuroforamen. The root must then be traced

Inferior articular processL4 Superiorarticular processL5 L5 root

Fig 3. Completion of central laminectomy trough. A combined (left and right) total of one facet remains, and the pars interarticularis is intact.

distally past the L5 pedicle and the foramen explored to ensure that there is no compression of the root within the foramen.

Decompression of Foraminal Zone Significant foraminal zone compromise may exist in degenerative spondylolisthesis. The exiting L4 nerve root is pinched between the posterior inferior edge of the vertebral body or the disk anteriorly, the pedicle superiorly, and the hypertrophic superior facet of the caudal vertebra inferiorly. Undercutting of the offending facet ensures that less than 50% of the facet joint is resected in most cases. 4 This part of the decompression is most safely performed with a Kerrison punch angled so as to parallel the nerve roots, which minimizes the risk of transection of the nerve roots. The facet joint may need to be thinned with a rongeur to safely place the Kerrison punch. Occasionally, a curette may be necessary to remove the inferomedial aspect of the pedicle to decompress the nerve root.

FUSION IN DEGENERATIVE SPONDYLOLISTHESIS A concomitant arthrodesis after decompressive laminectomy is recommended for patients with stenosis and degenerative spondylolisthesis. 5 The ideal technique for achieving an arthrodesis after a decompressive laminectomy is a bilateral lateral intertransverse or alo-transverse process fusion. For illustrative purposes, an L4-L5 arthrodesis is described. Exposure

Fig 2. Schematic cross section showing pathology in degenerative spondylolisthesis. The anteriorly eroded inferior articular process of L4 traps the traversing L5 nerve root in the lateral recess. SURGERY FOR SPINAL STENOSIS

The midline posterior approach used for decompression can be used to obtain exposure for the arthrodesis. Using hand-held retractors, the paraspinal muscles are pulled laterally and their attachment to the dorsolateral aspect of the facet joints released with electrocautery. Probing ven45

t-rally from here, the transverse processes can be found just distal to the facet joint• The L4 transverse process can be found just distal to the L3-L4 facet joint and the L5 transverse process found just distal to the L4-L5 facet joint. The retractors are reapplied to a position just dorsal to the transverse processes. Using a no. 2 curet or electrocautery, soft tissue is then removed from the dorsal aspect of the transverse processes, as well as the lateral aspects of the superior facets of L4 and L5. Soft tissue inserting onto the superior, inferior, and lateral edges of the transverse processes is released• Soft tissue is then removed from the lateral aspect of the pars interarticularis of L4, and from the junction of the superior facets with the transverse process, which is often recessed medially beneath an overhanging articular process. A flat bed is now available for laying down bone graft.

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Decortication is performed using a high-speed no. 4 or no. 5 round cutting bur, or with the use of curettes. The structures to be decorticated include the dorsal aspects of the L4 and L5 transverse processes, the lateral aspects of the superior articular facets of L4 and L5, and the lateral aspect of the pars interarticularis. 6

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Fig 5. Lateral view of pelvis showing a portion of the osteotome remaining outside the ilium while the other portion cuts through the outer corticocancellous table of the posterior ilium. A straight osteotome is used to make successive vertical cuts approximately 7 mm apart (Reprinted with permissionS).

Bone Grafting Autogenous bone graft should consist of long thin strips• Cancellous strips are ideally placed in direct contact with the decorticated areas of bone, over the transverse processes and adjacent to the superior articular processes (Fig 4). Cortical or corticocancellous strips also may be added.

Bone Graft Harvesting Access for bone graft harvest is either through a separate skin incision over the posterior iliac crest, or, if the laminectomy skin incision is long enough and distal enough, through subcutaneous dissection that allows access to the posterior iliac crest. The periosteum over the iliac crest is incised, and the muscles covering the outer table of the posterior ilium stripped subperiosteally. This is

usually performed with the Cobb elevator, using electrocoagulation to stop bleeding along the way. A Taylor retractor is then placed deep in the wound, and held in place by a small weight suspended from its handle• A half-inch straight osteotome is then used to make cuts in the outer cortex of the posterior ilium, beginning at the posterior iliac crest, and proceeding in a ventral direction• Only one half of the osteotome's distal edge should project into the intramedullary cavity; the other half should project out of the outer table. Successive vertical cuts of equal length are made approximately 7 mm apart (Fig 5). A half-inch curved osteotome is then used to connect the cuts

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46

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at their most ventral aspect. Beginning at the crest, the curved osteotome is then malleted ventrally b e t w e e n the two tables of the ilium, to remove corticocancellous strips of bone (Fig 6). Cancellous bone from the intramedullary cavity can n o w be harvested with gouges. Finally, curettes are used to r e m o v e any remaining cancellous bone.

INSTRUMENTATION The role of n o n i n s t r u m e n t e d versus i n s t r u m e n t e d arthrodesis in spinal stenosis surgery has not been well established in the literature. Internal fixation permits correction of deformity, provides stability, and improves the fusion rate. 7 We w o u l d r e c o m m e n d the use of instrumentation in the following conditions: (1) previous lumbar decompression with progressive spondylolisthesis, (2) recurrent stenosis with removal of s u m total of one facet joint, (3) scoliosis with a flexible curve or d o c u m e n t e d preoperative curve progression, (4) previous lumbar decompression with scoliosis, (5) symptomatic pseudoarthrosis w h e r e compression m a y b y helpful, (6) fusion of two or more segments, and (7) translational instability > 4 m m or angular instabil-

SURGERY FOR SPINAL STENOSIS

ity greater than 10 degrees end plate angle w h e n c o m p a r e d with segments above and below.

REFERENCES 1. Kirkaldy-Willis WH, Wedge JH, Yong-Hing K, et al: Pathology and pathogenesis of lumbar spondylosis and stenosis. Spine 3:319-328, 1978 2. Grobler LJ, Robertson PA, Novotny JE, et ah Decompression for degenerative spondylolisthesis and spinal stenosis at L4-5: The effects of facet joint morphology. Spine 18:1475-1482,1993 3. Abumi K, Panjabi M, Kramer K, et al: Biomechanical evaluation of lumbar spinal stability after graded facetectomies.Spine 15:1142-1147, 1990 4. Getty CJ, Johnson JR, Kirwan EO, et al: Partial undercutting fasciectomy for bony entrapment of the lumbar nerve root. J Bone Joint Surg Br 63:330-335,1981 5. Herkowitz HN, Kurz LT: Degenerative lumbar spondylolisthesis with spinal stenosis: A prospective study comparing decompression with decompression and intertransverse process arthrodesis. J Bone Joint Surg Am 73:802-808,1991 6. Kurz LT, Herkowitz HN: Techniques of spinal arthrodesis and bone graft harvest. Semin Spine Surg 6:124-127,1994 7. Bridwell KH, Sedgewick TA, O'Brien MF, et al: The role of fusion and instrumentation in the treatment of degenerative spondylolisthesis with spinal stenosis. J Spinal Disord 6:461-472,1993

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