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Surgical Management of Degenerative and Postsurgical Spondylolisthesis
Surgical Management of Degenerative and Postsurgical Spondylolisthesis John R. Dimar, II, MD, Mladen Djurasovic, MD, and Leah Y. Carreon, MD Spondylolisthesis is defined as the forward translation of one vertebra on another in the sagittal plane. There are multiple etiologies of spondylolisthesis, including the degenerative and postsurgical varieties. Degenerative spondylolisthesis presents in a more elderly population and usually involves the lumbar fourth and fifth vertebrae. The pathogenesis is believed to be secondary to the progressive degeneration of the disc and facets, which results in instability and pathologic segmental motion. Clinically, patients present with low back pain and neurological symptoms consisting of spinal claudication or radiculopathy. A postsurgical spondylolisthesis is often the inevitable result of decompression with up to 50% of patients developing late instability that requires stabilization. Similar to a degenerative spondylolisthesis, these patients will present with reoccurrence of radicular pain associated with increasing low back pain. A spondylolisthesis is identified with plain radiographs, which should include flexion and extension to identify pathologic motion. An MRI is useful for the evaluation of stenosis, while a Myelo/CT with flexion and extension weight-bearing views is superior for the evaluation of dynamic instability. Nonoperative treatment consists of bracing, nonsteroidal antiinflammatory medication, epidural blocks, weight reduction, and physical therapy. Surgical indications include severe back pain or neurological symptoms. Following decompression, an arthrodesis is recommended for a degenerative spondylolisthesis since long-term studies have demonstrated improved outcomes. A postsurgical spondylolisthesis, by definition, is unstable and requires a concurrent stabilization. Surgical options include posterior pedicular rod and screw fixation, posteriorly placed interbody implants combined with pedicular instrumentation, or combined anterior and posterior procedures. Materials available for fusion include autograft, allograft, or new biologic graft substitutes such as rhBMP-2. This article reviews the etiology and pathogenesis of spondylolisthesis along with recommended treatment options and surgical techniques to enable clinicians to insure superior patient treatment outcomes. Semin Spine Surg 17:186-194 © 2005 Elsevier Inc. All rights reserved. KEYWORDS spondylolisthesis, spine fusion, lumbar spine
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pondylolisthesis is defined as the forward translation of one vertebra on another in the sagittal plane of the spine. There are multiple etiologies of spondylolisthesis including dysplastic, isthmic, degenerative, traumatic, pathologic, and iatrogenic/ postsurgical.1 The degree of forward translation may be graded according to the Meyerding classification.2 Spondylolisthesis of the isthmic variety is asymptomatic during adult life and rarely progresses.3 When isthmic spondylolisthesis progresses, the result is back pain and radiculopathy.
University of Louisville, Department of Orthopedic Surgery, Leatherman Spine Center, Louisville, KY. Address reprint requests to John R. Dimar, II, MD, 210 East Gray Street, #900, Louisville, KY 40202-3900. E-mail: [email protected]
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Degenerative spondylolisthesis presents in a more elderly population and usually involves the lumbar fourth and fifth vertebra. Clinical symptoms at presentation include back pain, radiculopathy, and spinal claudication. In fact, degenerative spondylolisthesis is one of the most common causes of spinal stenosis in the elderly population. Unlike an isthmic spondylolisthesis, degenerative spondylolisthesis does not exhibit any abnormalities of the pars interarticularis; however, the pathogenesis is not well-defined. It is believed that with aging of the spine, the disc degenerates, moving the axis of rotation of the functional spinal unit posteriorly resulting in ligamentum flavum, interspinous ligament, and facet hypertrophy. Certain patients subsequently develop facet incompetence that allows for anterolisthesis of one vertebra on
Degenerative and postsurgical spondylolisthesis another, leading to central and lateral stenosis. This slow continuum of progressive degeneration leads to static spinal stenosis due to the facet and ligamentous hypertrophy with secondary dynamic stenosis due to the pathologic segmental motion. Certain patients that have sagittally oriented facets have a distinct predilection for the development of a degenerative spondylolisthesis between L4 and L5.4 Nonetheless, some patients with degenerative spondylolistheses may become stable secondary to hypertrophic ankylosis of the facets. Subsequently, the adjacent level may develop a symptomatic degenerative spondylolisthesis with neural compression. This effect is demonstrated by the prevalence of degenerative spondylolisthesis between the fourth and fifth lumbar vertebra secondary to either the stabilizing effect that the transverse processes’ alar ligaments imparts to the fifth vertebra or the sacralization of the fifth lumbar vertebra to the sacrum. The neurological symptoms caused by a degenerative spondylolithesis are secondary to the degenerative disc disease, disc protrusion, and the facet hypertrophy, which when combined with mechanical antero- or retrolisthesis results in both static and dynamic foraminal narrowing and neural impingement. A postsurgical spondylolisthesis often is the inevitable result of decompression, where it is necessary to extensively resect the facets to adequately decompress the entrapped nerve roots. Experimental studies have shown that excessive removal of the stabilizing structures of the spine results in either rotational or sagittal instability.5,6 Although the actual incidence is unknown, as many as 50% of patients that have had extensive facet, disc, and ligamentous resection for spinal stenosis will develop late instability requiring stabilization.7 Consequently, in the presence of spinal stenosis secondary to a preexisting spondylolisthesis, spinal arthrodesis following decompression has demonstrated superior long-term results.8
Diagnostic Modalities Spondylolisthesis is easily identified with plain radiographs, which should include oblique views to identify a possible pars interarticularis fracture. Most degenerative and postsurgical spondylolisthesis are Grade I or II, but may rarely progress to a higher grade slip. Dynamic flexion and extension sagittal radiographs are essential to identify any excessive pathologic segmental translation that might result in neural compression (Fig. 1). This finding is frequently a hallmark of dynamic instability, a condition that may be made significantly worse by an isolated decompression. On occasion, there may be enough motion at the level of the spondylolisthesis that the caudad vertebral body suffers progressive erosion, or in the case of the sacrum, a dome shape. However, this radiographic finding is uncommon with a degenerative or postsurgical spondylolisthesis, being noted primarily with isthmic spondylolisthesis that is typical in a younger population. Magnetic resonance imaging (MRI) is useful to identify central and/or lateral recess stenosis and is superior at identifying degenerative disc disease, tumors, intraspinal abnormalities, and acute spondylysis of the pars interarticularis
187 (Fig. 2). However, since MRI is performed in the recumbent position, a mobile spondylolisthesis may be reduced into a normal anatomical position obscuring any dynamic compression of the neural elements. Upright MRI has recently been introduced, but is not readily available. CT myelography provides the most reliable method to fully evaluate both the static (recumbent) and the dynamic (weight-bearing) pathology of a degenerative or postsurgical spondylolisthesis. Since the myelogram duplicates the dynamic position of the vertebra during weight-bearing, it provides a real-time picture of the degree and level(s) of neurological compromise. The importance of flexion and extension lateral views cannot be overstated, since they may provide the only information as to whether or not a concurrent stabilization procedure is required (Fig. 3). The CT scan is also superior to an MRI in evaluating the bony anatomy of the spine. Sagittal fine-cut reconstruction images are excellent in evaluating the foramen for hypertrophic facet impingement, canal diameter, ossification of the posterior longitudinal ligament, and ligamentum flavum. A CT myelography is also superior for evaluating malpositioned implants, since metallic implants (including titanium) will obscure any useful findings of an MRI due to image distortion. Finally, a CT myelography may also reveal spinal stenosis secondary to adjacent level degenerative or postsurgical spondylolisthesis.
Conservative Treatment Nonoperative treatment of degenerative spondylolisthesis may be appropriate depending on the degree of instability or severity of neural compression. Treatment modalities include nonsteroidal antiinflammatory medications (NSAIDs), limitation of activities up to and including short-term bed rest, bracing or casting, weight reduction, and physical therapy. An exercise program should be gradual and consist of lowimpact aerobic activity such as water aerobics, elliptical trainers, recumbent bicycles, and walking. Epidural injections may be beneficial for patients that exhibit radiculopathy or spinal claudication symptoms, but they have limited longterm benefit. While a combination of these treatment modalities may achieve satisfactory results temporarily, a significant number of patients with severe spinal stenosis due to degenerative spondylolisthesis will ultimately require surgery.9
Surgical Indications Surgical treatment of degenerative and postsurgical spondylolisthesis is indicated when nonoperative therapy has failed. Depending on the circumstances, either decompression or combined decompression with concurrent instrumented fusion may be indicated. The major indications for surgery include severe radiculopathy, neurogenic claudication, or incapacitating low back pain; all of which individually or in combination are a result of segmental spinal instability and the resultant spinal canal narrowing. The pathogenesis of nerve compression is twofold. The first cause is narrowing of the central spinal canal from displacement anteriorly of one vertebra on another. The second
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Figure 1 A 63-year-old female with progressive neurogenic claudication and a one-block walking tolerance. Lateral radiograph showing Grade 1 spondylolisthesis at L4 to L5 with a sacralized L5. Flexion and extension films show segmental translation at L4 to L5.
cause is due to the degenerative facet, capsule, and ligamentum flavum hypertrophy. Degeneration of the disc increases the load sharing by the facets resulting in hypertrophy and in eventual incompetence. Facet hypertrophy also leads to lateral recess narrowing and compression of the L4 and L5 nerve roots between the facets and the L5 vertebral body.
Understanding that the pathology consists of both neural compression secondary to these bony abnormalities and vertebral translation is critical to selecting the correct surgical procedure. This will prevent a subsequent surgery for postsurgical instability or persistent lateral recess stenosis. Postsurgical spondylolisthesis is frequently encountered
Degenerative and postsurgical spondylolisthesis
189 section, which may consequently render the level unstable, particularly in rotation. In these circumstances, where the true bony anatomy of the facet is obscured by capsular hypertrophy and spondylolysis, it is extremely difficult to gauge the actual amount of facet resection that occurs during a decompression, since only removal of the capsule will reveal the true amount of facet damage. Because of this dilemma, many decompressions that are extensive enough to relieve neural element compression, particularly in the lateral recess, result in subsequent postsurgical instability. Therefore, symptomatic postsurgical spondylolisthesis generally requires both decompression and stabilization with revision surgery, since more stabilizing structures will necessarily be resected during decompression.
Decompression with Instrumentation and Arthrodesis
Figure 2 A 46-year-old female with Grade 1 spondylolisthesis, severe degenerative disc disease, and bilateral L5 radiculopathy. (A) Axial MRI through L4 to L5 showing central and foraminal stenosis. (B) Sagittal MRI demonstrating Grade 1 L4 to L5 spondylolisthesis with consequent stenosis.
either when a preexisting mobile degenerative spondylolisthesis is decompressed without a concurrent fusion or as a result of a stable motion segment being rendered unstable following excessive facet, disc, and ligamentous resection (Fig. 4). An appreciation of the facet architecture during decompression is critical, since the facet orientation changes from coronal to sagittal as one moves cephalad from the lumbosacral junction. As a result, a larger proportion of lumbar rotatory motion is in the middle lumbar segments rather than at the lumbosacral junction.10 Traditional thought has been that 50% of each facet may be safely resected without rendering the spinal segment unstable.7 This paradigm is not appropriate for the upper segments of the spine where it frequently results in excessive superior articulating facet re-
Current opinion concerning the surgical treatment of degenerative spondylolisthesis, particularly those that demonstrate excessive pathological motion, is that an arthrodesis should be combined with a decompressive laminectomy. Concurrent pedicle instrumentation may also be used and has been shown to lead to a higher fusion rate, but no difference in clinical outcome.11 Long-term prospective studies have also demonstrated improved outcomes for degenerative spondylolisthesis when fusion is combined with decompression.8,12,14 The indication for an arthrodesis is that further resection of any hypertrophied structures, no matter how minimal, may result in increased pathological instability resulting in further slippage. The more extensive resection necessary to achieve an adequate decompression, the higher the incidence of progression of the spondylolisthesis. Therefore, when considering a wide decompression for spinal stenosis secondary to a degenerative spondylolisthesis, a segmental spinal arthrodesis is indicated.13 A decompression for spondylolisthesis is done in a similar fashion to that described for spinal stenosis. The anterior translation of one vertebra on another along with the frequently encountered extensive facet hypertrophy at the level of the spondylolisthesis makes identification of the anatomy and the subsequent decompression difficult. Following laminectomy, it is important to identify and decompress the exiting nerve root and not confuse it with the traversing nerve root. A thorough decompression of the neuroforamen via superior facet resection may be safely completed with small Kerrison rongeurs. Although rare with a degenerative or postsurgical spondylolisthesis, high-grade spondylolisthesis may need a complete nerve root decompression before reduction to prevent excessive stretching and resultant neurological injury.14 There is also often significant spinal dural hypoplasia secondary to the long-standing severe spinal canal narrowing, and therefore, the risk of a dural tear is significant. Every precaution should be employed to prevent a dural tear due to the significant morbidity that results from this complication, including increased blood loss, neurological injury, and postoperative epidural hematoma.15,16
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Figure 3 A 59-year-old male with severe lumbar back pain and right leg pain. Lateral myelogram demonstrates filling defect at L4 to L5 due to Grade 1 spondylolisthesis and sacralized L5. Flexion and extension radiographs display abnormal motion at L4 to L5.
There are currently many surgical methods commonly employed to achieve symptomatic relief from degenerative spondylolisthesis. Improved clinical outcomes have been documented by outcome studies following decompression and fusion using rigid pedicular/rod fixation.17 An alternative
popular methodology replaces the posterolateral arthrodesis with a posteriorly placed interbody fusion combined with structural interbody support. This is typified by a translaminar interbody fusion (TLIF) or a posterior lateral interbody fusion (PLIF).18,19 Currently, both approaches use supple-
Degenerative and postsurgical spondylolisthesis
Figure 4 A 52-year-old female following extensive laminectomy at L4 to L5 and L5 to S1 presenting with severe back pain and weakness of the left EHL. (A) Anteroposterior radiograph shows a wide laminectomy. (B) Lateral myelogram demonstrates Grade 1 spondylolisthesis at L4 to L5. (C, D) Flexion and upright myelogram show an increase in the forward translation of L4 on L5.
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192 mental posterior rigid pedicular/rod fixation and can be combined with a concurrent posterolateral arthrodesis if desired. Regardless of whether a posterolateral or an interbody technique is utilized, a standard midline approach to the spine is accomplished by reflecting the paraspinal muscles subperiosteally off the posterior spinous processes, lamina, and facet capsules. The integrity of the facet capsules and interspinous ligaments should be preserved until the correct surgical levels are identified. Meticulous attention to hemostasis will help prevent excessive blood loss. A localizing radiograph is essential to correct level identification, with either a probe placed within the disc space of the intended decompression and arthrodesis level or a pedicle probe placed into the pedicle of the superior vertebra. For a posterolateral arthrodesis, meticulous removal of all soft tissue from the posterior bony surfaces is essential since cell migration and fusion occurs from the decorticated bony surfaces.20 Although most degenerative and postsurgical spondylolisthesis demonstrate significant postural reduction on the operating table, some anterior translation of the cephalad vertebra on the caudad vertebra is inevitable. There is also distortion of the normal anatomy that may obscure the identification of the transverse processes, which are more ventrally positioned. This vertebral displacement becomes more pronounced as the grade of spondylolisthesis increases. To identify the cephalad ventrally displaced transverse process, it may be necessary to dissect along the prerenal fascia from the transverse processes above and below. Fortunately, the significant loss of fusion surface secondary to severe hypoplasia of the anterolisthesed vertebra’s transverse process observed with isthmic spondylolisthesis is not often observed with degenerative spondylolisthesis. When considering a posterolateral arthrodesis, a careful decortication of the transverse processes, pars interarticularis, posterior lamina, and facets are completed in preparation for placement of bone graft. Materials available for grafting include iliac crest (ICBG), local bone from the decompression, allograft, or newer biologic graft substitutes such as rhBMP-2 (Infuse™, Medtronic Sofamor Danek, Memphis, TN). Biologic fusion agents such as rhBMP-2 have demonstrated significant success in achieving excellent clinical outcomes in arthrodesis.21 Pedicle screw placement may be performed using any of the previously described techniques for spinal stenosis and should be used as an adjunct to posterolateral fusion. Instrumentation will improve the fusion rates and generally allow for more rapid mobilization postoperatively. Additionally, pedicle screw/rod instrumentation provides immediate stabilization to an unstable spinal segment and may aid in achieving and maintaining a reduction of the spondylolisthesis. Pedicle screw placement may be very difficult due to the distortion of anatomical landmarks and the tendency of the unstable, anterolisthesed, superior vertebra to move forward with pedicle probing. Unique to a degenerative spondylolisthesis is the tendency for the inferior pedicles to develop central sclerosis resulting in increased difficulty in successful cannulation of the pedicle with a probe. A high-speed burr may be necessary to perforate through the hard bone at the top of the pedicle and allow for successful pedicle probing.
J.R. Dimar, II, M. Djurasovic, and L.Y. Carreon Additionally, serial tapping of the pedicle is critical since aggressive screw placement, regardless of the screw having cutting flutes, can result in pedicle splitting and resultant loss of fixation the first time a patient flexes forward. With a higher grade, spondylolisthesis rod attachment may be difficult due to screw proximity and malalignment. This may be solved by utilizing longer multi-axial screws (although it is rare that a screw longer than 45 mm is needed) in the superior pedicles. Due to the potential for increased rotational and translational instability following decompression degenerative or postsurgical spondylolisthesis, placement of a crosslink should be considered to stiffen the construct. Intraoperative EMGs have demonstrated a 98% sensitivity in predicting whether a screw is within the pedicle and should be combined with postscrew placement radiographs to improve the accuracy of pedicle screw placement.22 Finally, before construct locking, attention should be paid to the maintenance of proper sagittal contour. As a rule, the safest time to consider the preservation or correction of lumbar lordosis is preoperatively, not during surgery, since this is the critical time to plan whether anterior column support via an anterior approach or TLIF procedure is necessary to restore segmental lordosis. The TLIF has gained popularity for arthrodesis due to its purported advantages of less lateral muscle dissection, disc space elevation with resultant foraminal opening, modest improvement of lordosis, achievement of a 360° fusion without the need for an expensive supplemental anterior approach, and its amenability to minimally invasive procedures19,23 (Fig. 5). This is countered by the potential for more circumferential epidural scarring, nerve root damage secondary to retraction, anterior perforation of the disc, potential for less effective fusion surface preparation, and the need for significant technical expertise. There is also the need for supplemental fixation of the operative level with pedicle screws and rods posteriorly. Both anterior interbody fusions and TLIF procedures have been shown to improve or maintain sagittal alignment. The TLIF has been shown to have slight settling or a decrease in height at 2-year follow-up.24 All the potential sources of bone grafts previously cited for use with a posterior lateral arthrodesis may be utilized with the TLIF procedure. The newer biologics such as rhBMP-2 have also demonstrated success. As well, the TLIF has spawned a variety of implants constructed of metal, carbon fiber, plastic, and bioabsorbable materials with each claiming superiority.25,26 There are, however, no clinical trials directly comparing the implants to support any claims. From the practical standpoint, any interbody implant and instrument system that allows for thorough endplate preparation for fusion, safe nerve retraction, instruments for the elevation of a collapsed disc space, and a well-fitting selection of implants that are stable within the disc space and allow for grafting material placement should be adequate to achieve a successful arthrodesis. Several authors have reported similar arthrodesis rates after TLIF to that of posterolateral arthrodesis.19,27 Many of these posteriorly placed interbody implants can also be utilized with minimally invasive techniques, and propo-
Degenerative and postsurgical spondylolisthesis
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Figure 5 A 55-year-old female with progressive back pain and bilateral leg pain. (A) Lateral radiograph shows Grade 1 spondylolisthesis at L4 to L5. (B) Axial MRI shows associated spinal stenosis with thickening of the ligamentum flavum. (C) Sagittal MRI shows thickened posterior longitudinal ligament and stenosis. (D) Postoperative lateral film shows acceptable reduction of spondylolisthesis at L4 to L5 with interbody fusion via a transforaminal approach supplemented by posterior arthrodesis with instrumentation.
nents of these techniques have reported similar rates of arthrodesis.28 The TLIF technique relies on the unilateral excision of a facet joint to gain access to the posterolateral disc space. A self-retaining laminar spreader or previously inserted pedicle screws are used to apply distraction to the disc space and facilitate exposure. The epidural veins are cauterized using bipolar electrocautery while taking care not to be too aggressive and cause excessive epidural scarring. The nerve root is carefully retracted toward the midline to prevent traction injury. Care must be exercised with any retraction of the exiting nerve root, which is generally sheathed in epidural fat, since it is vulnerable to a crush injury when vigorous
retraction compresses it against the pedicle. The disc is then excised and all material removed down to the endplates using various ronguers and curettes. Depending on the system, there is a wide variety of useful instruments to prepare the disc space for arthrodesis and implant placement. Instruments are also designed to open the disc space, elevate the disc height, decorticate the endplate, and safely expedite precise implant placement. Preferential choices of grafting material include autograft and a rhBMP-2/collagen sponge as allograft is less reliable.19 The interbody implants are available in a wide variety of materials, including titanium, plastics, resorbable polymers, and machined allograft bone,26 as well as numerous shapes, sizes, and configurations to facili-
J.R. Dimar, II, M. Djurasovic, and L.Y. Carreon
194 tate the restoration of lordosis. Accurate placement of the interbody implants may be facilitated by either intraoperative fluoroscopy or serial anterior and lateral radiographs. Regardless of the type of implant, meticulous disc preparation for fusion and correct interbody graft placement is important for success. Because of the facet resection and disc excision, significant destabilization of the spine occurs necessitating the use of supplemental pedicular screw/rod fixation. A TLIF may also be combined with a posterolateral arthrodesis if desired to ensure a more reliable arthrodesis.
12.
13.
14.
15.
Conclusions The purpose of this article was to review the current treatment of low back pain and radicular symptoms caused by degenerative or postsurgical spondylolistheses. It is important to evaluate each patient’s condition individually to determine which of the techniques outlined are applicable to their particular spinal pathology. Careful patient selection, thorough preoperative medical clearance, thoughtful surgical judgment, and proper training in the implementation of the various techniques will insure superior patient outcomes while minimizing complications.
References 1. Amundson G, Edwards CC, Garfin SR: Spondylolisthesis, in Rothman RH, Simeone FA (eds): Spine (ed 3). Vol. 11, Philadelphia, PA, WB Saunders, 1992, p 913 2. Meyerding HW: Spondylolisthesis. Surg Gynecol Obstet 54:371-377, 1932 3. Fredrickson BE: The natural history of spondylolysis and spondylolisthesis. J Bone Joint Surg 250:171-175, 1984 4. Boden SD, Riew KD, Yamaguchi K, et al: Orientation of the lumbar facet joints: association with degenerative disc disease. J Bone Joint Surg Am 78(3):403-411, 1996 5. Panjabi MM: The stabilizing system of the spine. Part I. Function, dysfunction, adaptation, and enhancement. J Spinal Disord 5(4):383389; discussion 397, 1992 6. Panjabi MM: The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. J Spinal Disord 5(4):390-396; discussion 397, 1992 7. Shields CB, Miller CA, Dunsker SB: Thoracic and lumbar spondylosis. Spine Surg Benzel 1:421-434, 1999 8. 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(6):802-808, 1991 9. Grobler LJ, Wiltse LL: Classification, nonoperative, and operative treatment of spondylolisthesis, in Frymoyer JW (ed): The Adult Spine: Principles and Practice. New York, NY, Raven Press, Vol. 2, 1991, pp 1655-1704 10. Zhang YM, Voor MJ, Wang M, et al: Intervertebral measurement of lumbar segmental motion with a new measuring device. Med Eng Phys 20(2):139-148, 1998 11. Fischgrund JS, Mackay M, Herkowitz HN, et al: 1997 Volvo Award Winner in Clinical Studies. Degenerative lumbar spondylolisthesis
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with spinal stenosis: a prospective, randomized study comparing decompressive laminectomy and arthrodesis with and without spinal instrumentation. Spine 22(24):2807-2812, 1997 Kornblum MB, Fischgrund JS, Herkowitz HN, et al: Degenerative lumbar spondylolisthesis with spinal stenosis: a prospective long-term study comparing fusion and pseudarthrosis. Spine 29(7):726-733; discussion 733-734, 2004 Herkowitz HN, Sidhu KS: Lumbar spine fusion in the treatment of degenerative conditions: current indications and recommendations. J Am Acad Orthop Surg 3(3):123-135, 1995 Hu SS, Bradford DS, Transfeldt EE, et al: Reduction of high-grade spondylolisthesis using Edwards instrumentation. Spine 21(3):367371, 1996 Bosacco SJ, Gardner MJ, Guille JT: Evaluation and treatment of dural tears in lumbar spine surgery: a review. Clin Orthop 389:238-247, 2001 Ehni BL, Benzel EC: Lumbar discectomy. Spine Surg Benzel 1:389-400, 1999 Nork SE, Hu SS, Workman KL, et al: Patient outcomes after decompression and instrumented posterior spinal fusion for degenerative spondylolisthesis. Spine 24(6):561-569, 1999 Hackenberg L, Halm H, Bullmann V, et al: Transforaminal lumbar interbody fusion: a safe technique with satisfactory three to five year results. Eur Spine J [Epub ahead of print], 2005 Mummaneni PV, Pan J, Haid RW, et al: Contribution of recombinant human bone morphogenetic protein-2 to the rapid creation of interbody fusion when used in transforaminal lumbar interbody fusion: a preliminary report. Invited submission from the Joint Section Meeting on Disorders of the Spine and Peripheral Nerves, March 2004. J Neurosurg Spine 1(1):19-23, 2004 Boden SD, Schimandle JH, Hutton WC, et al: 1995 Volvo Award in Basic Sciences. The use of an osteoinductive growth factor for lumbar spinal fusion. Part I: Biology of spinal fusion. Spine 15;20(24):26262632, 1995 Dimar JR, Glassman SD, Burkus JK, Carreon LY: A comparison of prospective clinical outcome measures for anterior vs. posterior singlelevel spine fusion. IMAST Program July 2004 Glassman SD, Dimar JR, Puno RM, et al: A prospective analysis of intraoperative electromyographic monitoring of pedicle screw placement with computed tomographic scan confirmation. Spine 20(12): 1375-1379, 1995 Hackenberg L, Halm H, Bullmann V, et al: Transforaminal lumbar interbody fusion: a safe technique with satisfactory three to five year results. Eur Spine J [Epub ahead of print], 2005 Brantigan JW, Neidre A: Achievement of normal sagittal plane alignment using a wedged carbon fiber reinforced polymer fusion cage in treatment of spondylolisthesis. Spine J 3(3):186-196, 2003 Brantigan JW, Steffee AD, Lewis ML, et al: Lumbar interbody fusion using the Brantigan I/F cage for posterior lumbar interbody fusion and the variable pedicle screw placement system: two-year results from a Food and Drug Administration investigational device exemption clinical trial. Spine 25(11):1437-1446, 2000 Kuklo TR, Rosner MK, Polly DW Jr: Computerized tomography evaluation of a resorbable implant after transforaminal lumbar interbody fusion. Neurosurg Focus 16(3):E10, 2004 Hackenberg L, Halm H, Bullmann V, et al: Transforaminal lumbar interbody fusion: a safe technique with satisfactory three to five year results. Eur Spine J. [Epub ahead of print], 2005 Schwender J, Ogilvie J: Spondylolisthesis treated with the cantilever transforaminal lumbar interbody fusion (c-TLIF): prospective radiographic and patient outcomes with a minimum of two years follow-up. IMAST Bermuda, 2004
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pondylolisthesis is defined as the forward translation of one vertebra on another in the sagittal plane of the spine. There are multiple etiologies of spondylolisthesis including dysplastic, isthmic, degenerative, traumatic, pathologic, and iatrogenic/ postsurgical.1 The degree of forward translation may be graded according to the Meyerding classification.2 Spondylolisthesis of the isthmic variety is asymptomatic during adult life and rarely progresses.3 When isthmic spondylolisthesis progresses, the result is back pain and radiculopathy.
University of Louisville, Department of Orthopedic Surgery, Leatherman Spine Center, Louisville, KY. Address reprint requests to John R. Dimar, II, MD, 210 East Gray Street, #900, Louisville, KY 40202-3900. E-mail: [email protected]
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Degenerative spondylolisthesis presents in a more elderly population and usually involves the lumbar fourth and fifth vertebra. Clinical symptoms at presentation include back pain, radiculopathy, and spinal claudication. In fact, degenerative spondylolisthesis is one of the most common causes of spinal stenosis in the elderly population. Unlike an isthmic spondylolisthesis, degenerative spondylolisthesis does not exhibit any abnormalities of the pars interarticularis; however, the pathogenesis is not well-defined. It is believed that with aging of the spine, the disc degenerates, moving the axis of rotation of the functional spinal unit posteriorly resulting in ligamentum flavum, interspinous ligament, and facet hypertrophy. Certain patients subsequently develop facet incompetence that allows for anterolisthesis of one vertebra on
Degenerative and postsurgical spondylolisthesis another, leading to central and lateral stenosis. This slow continuum of progressive degeneration leads to static spinal stenosis due to the facet and ligamentous hypertrophy with secondary dynamic stenosis due to the pathologic segmental motion. Certain patients that have sagittally oriented facets have a distinct predilection for the development of a degenerative spondylolisthesis between L4 and L5.4 Nonetheless, some patients with degenerative spondylolistheses may become stable secondary to hypertrophic ankylosis of the facets. Subsequently, the adjacent level may develop a symptomatic degenerative spondylolisthesis with neural compression. This effect is demonstrated by the prevalence of degenerative spondylolisthesis between the fourth and fifth lumbar vertebra secondary to either the stabilizing effect that the transverse processes’ alar ligaments imparts to the fifth vertebra or the sacralization of the fifth lumbar vertebra to the sacrum. The neurological symptoms caused by a degenerative spondylolithesis are secondary to the degenerative disc disease, disc protrusion, and the facet hypertrophy, which when combined with mechanical antero- or retrolisthesis results in both static and dynamic foraminal narrowing and neural impingement. A postsurgical spondylolisthesis often is the inevitable result of decompression, where it is necessary to extensively resect the facets to adequately decompress the entrapped nerve roots. Experimental studies have shown that excessive removal of the stabilizing structures of the spine results in either rotational or sagittal instability.5,6 Although the actual incidence is unknown, as many as 50% of patients that have had extensive facet, disc, and ligamentous resection for spinal stenosis will develop late instability requiring stabilization.7 Consequently, in the presence of spinal stenosis secondary to a preexisting spondylolisthesis, spinal arthrodesis following decompression has demonstrated superior long-term results.8
Diagnostic Modalities Spondylolisthesis is easily identified with plain radiographs, which should include oblique views to identify a possible pars interarticularis fracture. Most degenerative and postsurgical spondylolisthesis are Grade I or II, but may rarely progress to a higher grade slip. Dynamic flexion and extension sagittal radiographs are essential to identify any excessive pathologic segmental translation that might result in neural compression (Fig. 1). This finding is frequently a hallmark of dynamic instability, a condition that may be made significantly worse by an isolated decompression. On occasion, there may be enough motion at the level of the spondylolisthesis that the caudad vertebral body suffers progressive erosion, or in the case of the sacrum, a dome shape. However, this radiographic finding is uncommon with a degenerative or postsurgical spondylolisthesis, being noted primarily with isthmic spondylolisthesis that is typical in a younger population. Magnetic resonance imaging (MRI) is useful to identify central and/or lateral recess stenosis and is superior at identifying degenerative disc disease, tumors, intraspinal abnormalities, and acute spondylysis of the pars interarticularis
187 (Fig. 2). However, since MRI is performed in the recumbent position, a mobile spondylolisthesis may be reduced into a normal anatomical position obscuring any dynamic compression of the neural elements. Upright MRI has recently been introduced, but is not readily available. CT myelography provides the most reliable method to fully evaluate both the static (recumbent) and the dynamic (weight-bearing) pathology of a degenerative or postsurgical spondylolisthesis. Since the myelogram duplicates the dynamic position of the vertebra during weight-bearing, it provides a real-time picture of the degree and level(s) of neurological compromise. The importance of flexion and extension lateral views cannot be overstated, since they may provide the only information as to whether or not a concurrent stabilization procedure is required (Fig. 3). The CT scan is also superior to an MRI in evaluating the bony anatomy of the spine. Sagittal fine-cut reconstruction images are excellent in evaluating the foramen for hypertrophic facet impingement, canal diameter, ossification of the posterior longitudinal ligament, and ligamentum flavum. A CT myelography is also superior for evaluating malpositioned implants, since metallic implants (including titanium) will obscure any useful findings of an MRI due to image distortion. Finally, a CT myelography may also reveal spinal stenosis secondary to adjacent level degenerative or postsurgical spondylolisthesis.
Conservative Treatment Nonoperative treatment of degenerative spondylolisthesis may be appropriate depending on the degree of instability or severity of neural compression. Treatment modalities include nonsteroidal antiinflammatory medications (NSAIDs), limitation of activities up to and including short-term bed rest, bracing or casting, weight reduction, and physical therapy. An exercise program should be gradual and consist of lowimpact aerobic activity such as water aerobics, elliptical trainers, recumbent bicycles, and walking. Epidural injections may be beneficial for patients that exhibit radiculopathy or spinal claudication symptoms, but they have limited longterm benefit. While a combination of these treatment modalities may achieve satisfactory results temporarily, a significant number of patients with severe spinal stenosis due to degenerative spondylolisthesis will ultimately require surgery.9
Surgical Indications Surgical treatment of degenerative and postsurgical spondylolisthesis is indicated when nonoperative therapy has failed. Depending on the circumstances, either decompression or combined decompression with concurrent instrumented fusion may be indicated. The major indications for surgery include severe radiculopathy, neurogenic claudication, or incapacitating low back pain; all of which individually or in combination are a result of segmental spinal instability and the resultant spinal canal narrowing. The pathogenesis of nerve compression is twofold. The first cause is narrowing of the central spinal canal from displacement anteriorly of one vertebra on another. The second
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Figure 1 A 63-year-old female with progressive neurogenic claudication and a one-block walking tolerance. Lateral radiograph showing Grade 1 spondylolisthesis at L4 to L5 with a sacralized L5. Flexion and extension films show segmental translation at L4 to L5.
cause is due to the degenerative facet, capsule, and ligamentum flavum hypertrophy. Degeneration of the disc increases the load sharing by the facets resulting in hypertrophy and in eventual incompetence. Facet hypertrophy also leads to lateral recess narrowing and compression of the L4 and L5 nerve roots between the facets and the L5 vertebral body.
Understanding that the pathology consists of both neural compression secondary to these bony abnormalities and vertebral translation is critical to selecting the correct surgical procedure. This will prevent a subsequent surgery for postsurgical instability or persistent lateral recess stenosis. Postsurgical spondylolisthesis is frequently encountered
Degenerative and postsurgical spondylolisthesis
189 section, which may consequently render the level unstable, particularly in rotation. In these circumstances, where the true bony anatomy of the facet is obscured by capsular hypertrophy and spondylolysis, it is extremely difficult to gauge the actual amount of facet resection that occurs during a decompression, since only removal of the capsule will reveal the true amount of facet damage. Because of this dilemma, many decompressions that are extensive enough to relieve neural element compression, particularly in the lateral recess, result in subsequent postsurgical instability. Therefore, symptomatic postsurgical spondylolisthesis generally requires both decompression and stabilization with revision surgery, since more stabilizing structures will necessarily be resected during decompression.
Decompression with Instrumentation and Arthrodesis
Figure 2 A 46-year-old female with Grade 1 spondylolisthesis, severe degenerative disc disease, and bilateral L5 radiculopathy. (A) Axial MRI through L4 to L5 showing central and foraminal stenosis. (B) Sagittal MRI demonstrating Grade 1 L4 to L5 spondylolisthesis with consequent stenosis.
either when a preexisting mobile degenerative spondylolisthesis is decompressed without a concurrent fusion or as a result of a stable motion segment being rendered unstable following excessive facet, disc, and ligamentous resection (Fig. 4). An appreciation of the facet architecture during decompression is critical, since the facet orientation changes from coronal to sagittal as one moves cephalad from the lumbosacral junction. As a result, a larger proportion of lumbar rotatory motion is in the middle lumbar segments rather than at the lumbosacral junction.10 Traditional thought has been that 50% of each facet may be safely resected without rendering the spinal segment unstable.7 This paradigm is not appropriate for the upper segments of the spine where it frequently results in excessive superior articulating facet re-
Current opinion concerning the surgical treatment of degenerative spondylolisthesis, particularly those that demonstrate excessive pathological motion, is that an arthrodesis should be combined with a decompressive laminectomy. Concurrent pedicle instrumentation may also be used and has been shown to lead to a higher fusion rate, but no difference in clinical outcome.11 Long-term prospective studies have also demonstrated improved outcomes for degenerative spondylolisthesis when fusion is combined with decompression.8,12,14 The indication for an arthrodesis is that further resection of any hypertrophied structures, no matter how minimal, may result in increased pathological instability resulting in further slippage. The more extensive resection necessary to achieve an adequate decompression, the higher the incidence of progression of the spondylolisthesis. Therefore, when considering a wide decompression for spinal stenosis secondary to a degenerative spondylolisthesis, a segmental spinal arthrodesis is indicated.13 A decompression for spondylolisthesis is done in a similar fashion to that described for spinal stenosis. The anterior translation of one vertebra on another along with the frequently encountered extensive facet hypertrophy at the level of the spondylolisthesis makes identification of the anatomy and the subsequent decompression difficult. Following laminectomy, it is important to identify and decompress the exiting nerve root and not confuse it with the traversing nerve root. A thorough decompression of the neuroforamen via superior facet resection may be safely completed with small Kerrison rongeurs. Although rare with a degenerative or postsurgical spondylolisthesis, high-grade spondylolisthesis may need a complete nerve root decompression before reduction to prevent excessive stretching and resultant neurological injury.14 There is also often significant spinal dural hypoplasia secondary to the long-standing severe spinal canal narrowing, and therefore, the risk of a dural tear is significant. Every precaution should be employed to prevent a dural tear due to the significant morbidity that results from this complication, including increased blood loss, neurological injury, and postoperative epidural hematoma.15,16
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Figure 3 A 59-year-old male with severe lumbar back pain and right leg pain. Lateral myelogram demonstrates filling defect at L4 to L5 due to Grade 1 spondylolisthesis and sacralized L5. Flexion and extension radiographs display abnormal motion at L4 to L5.
There are currently many surgical methods commonly employed to achieve symptomatic relief from degenerative spondylolisthesis. Improved clinical outcomes have been documented by outcome studies following decompression and fusion using rigid pedicular/rod fixation.17 An alternative
popular methodology replaces the posterolateral arthrodesis with a posteriorly placed interbody fusion combined with structural interbody support. This is typified by a translaminar interbody fusion (TLIF) or a posterior lateral interbody fusion (PLIF).18,19 Currently, both approaches use supple-
Degenerative and postsurgical spondylolisthesis
Figure 4 A 52-year-old female following extensive laminectomy at L4 to L5 and L5 to S1 presenting with severe back pain and weakness of the left EHL. (A) Anteroposterior radiograph shows a wide laminectomy. (B) Lateral myelogram demonstrates Grade 1 spondylolisthesis at L4 to L5. (C, D) Flexion and upright myelogram show an increase in the forward translation of L4 on L5.
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192 mental posterior rigid pedicular/rod fixation and can be combined with a concurrent posterolateral arthrodesis if desired. Regardless of whether a posterolateral or an interbody technique is utilized, a standard midline approach to the spine is accomplished by reflecting the paraspinal muscles subperiosteally off the posterior spinous processes, lamina, and facet capsules. The integrity of the facet capsules and interspinous ligaments should be preserved until the correct surgical levels are identified. Meticulous attention to hemostasis will help prevent excessive blood loss. A localizing radiograph is essential to correct level identification, with either a probe placed within the disc space of the intended decompression and arthrodesis level or a pedicle probe placed into the pedicle of the superior vertebra. For a posterolateral arthrodesis, meticulous removal of all soft tissue from the posterior bony surfaces is essential since cell migration and fusion occurs from the decorticated bony surfaces.20 Although most degenerative and postsurgical spondylolisthesis demonstrate significant postural reduction on the operating table, some anterior translation of the cephalad vertebra on the caudad vertebra is inevitable. There is also distortion of the normal anatomy that may obscure the identification of the transverse processes, which are more ventrally positioned. This vertebral displacement becomes more pronounced as the grade of spondylolisthesis increases. To identify the cephalad ventrally displaced transverse process, it may be necessary to dissect along the prerenal fascia from the transverse processes above and below. Fortunately, the significant loss of fusion surface secondary to severe hypoplasia of the anterolisthesed vertebra’s transverse process observed with isthmic spondylolisthesis is not often observed with degenerative spondylolisthesis. When considering a posterolateral arthrodesis, a careful decortication of the transverse processes, pars interarticularis, posterior lamina, and facets are completed in preparation for placement of bone graft. Materials available for grafting include iliac crest (ICBG), local bone from the decompression, allograft, or newer biologic graft substitutes such as rhBMP-2 (Infuse™, Medtronic Sofamor Danek, Memphis, TN). Biologic fusion agents such as rhBMP-2 have demonstrated significant success in achieving excellent clinical outcomes in arthrodesis.21 Pedicle screw placement may be performed using any of the previously described techniques for spinal stenosis and should be used as an adjunct to posterolateral fusion. Instrumentation will improve the fusion rates and generally allow for more rapid mobilization postoperatively. Additionally, pedicle screw/rod instrumentation provides immediate stabilization to an unstable spinal segment and may aid in achieving and maintaining a reduction of the spondylolisthesis. Pedicle screw placement may be very difficult due to the distortion of anatomical landmarks and the tendency of the unstable, anterolisthesed, superior vertebra to move forward with pedicle probing. Unique to a degenerative spondylolisthesis is the tendency for the inferior pedicles to develop central sclerosis resulting in increased difficulty in successful cannulation of the pedicle with a probe. A high-speed burr may be necessary to perforate through the hard bone at the top of the pedicle and allow for successful pedicle probing.
J.R. Dimar, II, M. Djurasovic, and L.Y. Carreon Additionally, serial tapping of the pedicle is critical since aggressive screw placement, regardless of the screw having cutting flutes, can result in pedicle splitting and resultant loss of fixation the first time a patient flexes forward. With a higher grade, spondylolisthesis rod attachment may be difficult due to screw proximity and malalignment. This may be solved by utilizing longer multi-axial screws (although it is rare that a screw longer than 45 mm is needed) in the superior pedicles. Due to the potential for increased rotational and translational instability following decompression degenerative or postsurgical spondylolisthesis, placement of a crosslink should be considered to stiffen the construct. Intraoperative EMGs have demonstrated a 98% sensitivity in predicting whether a screw is within the pedicle and should be combined with postscrew placement radiographs to improve the accuracy of pedicle screw placement.22 Finally, before construct locking, attention should be paid to the maintenance of proper sagittal contour. As a rule, the safest time to consider the preservation or correction of lumbar lordosis is preoperatively, not during surgery, since this is the critical time to plan whether anterior column support via an anterior approach or TLIF procedure is necessary to restore segmental lordosis. The TLIF has gained popularity for arthrodesis due to its purported advantages of less lateral muscle dissection, disc space elevation with resultant foraminal opening, modest improvement of lordosis, achievement of a 360° fusion without the need for an expensive supplemental anterior approach, and its amenability to minimally invasive procedures19,23 (Fig. 5). This is countered by the potential for more circumferential epidural scarring, nerve root damage secondary to retraction, anterior perforation of the disc, potential for less effective fusion surface preparation, and the need for significant technical expertise. There is also the need for supplemental fixation of the operative level with pedicle screws and rods posteriorly. Both anterior interbody fusions and TLIF procedures have been shown to improve or maintain sagittal alignment. The TLIF has been shown to have slight settling or a decrease in height at 2-year follow-up.24 All the potential sources of bone grafts previously cited for use with a posterior lateral arthrodesis may be utilized with the TLIF procedure. The newer biologics such as rhBMP-2 have also demonstrated success. As well, the TLIF has spawned a variety of implants constructed of metal, carbon fiber, plastic, and bioabsorbable materials with each claiming superiority.25,26 There are, however, no clinical trials directly comparing the implants to support any claims. From the practical standpoint, any interbody implant and instrument system that allows for thorough endplate preparation for fusion, safe nerve retraction, instruments for the elevation of a collapsed disc space, and a well-fitting selection of implants that are stable within the disc space and allow for grafting material placement should be adequate to achieve a successful arthrodesis. Several authors have reported similar arthrodesis rates after TLIF to that of posterolateral arthrodesis.19,27 Many of these posteriorly placed interbody implants can also be utilized with minimally invasive techniques, and propo-
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Figure 5 A 55-year-old female with progressive back pain and bilateral leg pain. (A) Lateral radiograph shows Grade 1 spondylolisthesis at L4 to L5. (B) Axial MRI shows associated spinal stenosis with thickening of the ligamentum flavum. (C) Sagittal MRI shows thickened posterior longitudinal ligament and stenosis. (D) Postoperative lateral film shows acceptable reduction of spondylolisthesis at L4 to L5 with interbody fusion via a transforaminal approach supplemented by posterior arthrodesis with instrumentation.
nents of these techniques have reported similar rates of arthrodesis.28 The TLIF technique relies on the unilateral excision of a facet joint to gain access to the posterolateral disc space. A self-retaining laminar spreader or previously inserted pedicle screws are used to apply distraction to the disc space and facilitate exposure. The epidural veins are cauterized using bipolar electrocautery while taking care not to be too aggressive and cause excessive epidural scarring. The nerve root is carefully retracted toward the midline to prevent traction injury. Care must be exercised with any retraction of the exiting nerve root, which is generally sheathed in epidural fat, since it is vulnerable to a crush injury when vigorous
retraction compresses it against the pedicle. The disc is then excised and all material removed down to the endplates using various ronguers and curettes. Depending on the system, there is a wide variety of useful instruments to prepare the disc space for arthrodesis and implant placement. Instruments are also designed to open the disc space, elevate the disc height, decorticate the endplate, and safely expedite precise implant placement. Preferential choices of grafting material include autograft and a rhBMP-2/collagen sponge as allograft is less reliable.19 The interbody implants are available in a wide variety of materials, including titanium, plastics, resorbable polymers, and machined allograft bone,26 as well as numerous shapes, sizes, and configurations to facili-
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194 tate the restoration of lordosis. Accurate placement of the interbody implants may be facilitated by either intraoperative fluoroscopy or serial anterior and lateral radiographs. Regardless of the type of implant, meticulous disc preparation for fusion and correct interbody graft placement is important for success. Because of the facet resection and disc excision, significant destabilization of the spine occurs necessitating the use of supplemental pedicular screw/rod fixation. A TLIF may also be combined with a posterolateral arthrodesis if desired to ensure a more reliable arthrodesis.
12.
13.
14.
15.
Conclusions The purpose of this article was to review the current treatment of low back pain and radicular symptoms caused by degenerative or postsurgical spondylolistheses. It is important to evaluate each patient’s condition individually to determine which of the techniques outlined are applicable to their particular spinal pathology. Careful patient selection, thorough preoperative medical clearance, thoughtful surgical judgment, and proper training in the implementation of the various techniques will insure superior patient outcomes while minimizing complications.
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