Surgical Management of Isthmic, Dysplastic and Degenerative Spondylolisthesis

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CHAPTER 100 Surgical Management of Isthmic, Dysplastic and Degenerative Spondylolisthesis

Yizhar Floman

INTRODUCTION

Spondylolisthesis is a common radiological and clinical condition that may arise as a result of different developmental and pathological processes. Although the classification system proposed by Wiltse, Newman, and McNab is the most widely accepted ¹ there is no consensus which classification system is the most appropriate for clinical decision-making.¹^–³ Most authorities agree that the presence or absence of an isthmic defect or elongated pars in conjunction with the presence or absences of dysplastic changes are the most important features of any classification system.^2,³ Some types of spondylolisthesis occur only in adults (i.e. degenerative), while others are encountered mostly in children and adolescents (dysplastic). Although isthmic spondylolisthesis is present in both children and adolescents as well as in adults, the clinical presentation and natural history of this type of spondylolisthesis differ in the two age groups. It is obvious, therefore, that the recommended management of isthmic spondylolisthesis in adolescents may differ from the desirable management in adults.

Some types of spondylolisthesis require simple and standard surgical management, others require the most complex and challenging surgery. Many reports on the surgical management of spondylolisthesis lump together different types of spondylolisthesis, different age groups, and are at best anecdotal and retrospective. Only a few well-conducted outcome studies ⁴^–⁶ on the surgical management of spondylolisthesis have been published on well-defined populations with similar types of vertebral slip (isthmic or degenerative). It is not surprising, therefore, that the surgical management of the various types of spondylolisthesis is not yet standardized and depends among other factors on the severity of the slip. Therefore, the type and extent of the surgical management is often controversial. This controversy is well reflected in the literature.⁷

The goal of surgery in spondylolisthesis is to reconstruct the normal anatomy whenever possible (pars repair), to restore the normal sagittal profile of the spine (reduction), to sacrifice as few motion segments as possible and, by doing the above, alleviate back and leg pain to promote daily and recreational activities. Since there is no standard type of operation, the most suitable surgical solution should be tailored to the individual case, taking into consideration not only gender, chronological age, and the amount of the slip but also the presence of dysplastic and/or degenerative changes, as well as the global sagittal balance.

The most common types of spondylolisthesis encountered clinically are isthmic, dysplastic, and degenerative, and these types will be discussed in detail in this chapter. The rare types of spondylolisthesis such as traumatic, pathologic, or iatrogenic will not be discussed in this chapter, although these should be managed according to the same guidelines outlined throughout the chapter.

INDICATIONS FOR SURGERY

The indications for surgical intervention in spondylolisthesis are the same as in any other spinal pathology: pain that does not respond to medical rehabilitation and interventional spine management, functional impairment, neurological deficit, and progressive deformity (vertebral slip).

Adolescents

Wiltse and Jackson ⁸ outlined the guidelines for the management of spondylolysis and spondylolisthesis in children. Failure of adequate conservative management (discussed in the previous chapter), may dictate the need for surgical intervention, including surgical stabilization.⁹ In general, most low-grade isthmic slips are managed successfully with nonoperative treatment and only one-third of patients will require surgery.¹⁰ Adolescents and young adults with spondylolysis may be managed with pars interarticularis repair. Surgical stabilization should be strongly considered, in symptomatic adolescents with slips between 25% and 50%, and in asymptomatic individuals in whom slip progression is documented radiologically. Surgical stabilization is mandatory in slips greater than 50%, or when the slip angle exceeds 45 degrees, even in the absence of symptoms, as further slip progression will certainly occur.^8,^11,¹²

Adults

In adults with low back pain and/or sciatica, the mere presence of spondylolysis or minimal olisthesis is not by itself an indication for surgery. Symptoms may not be directly related to these abnormalities, which probably developed many years prior to the current complaint. The cause of pain may be the result of a lesion elsewhere in the spine. Nevertheless, after the fourth decade of life some adults with a mild slip present with back and leg pain, due to superimposed degenerative changes either at the slip level or at the level above the spondylolisthesis. In addition, adult slip progression secondary to the degeneration of the disc at the slip level may occur in up to 20% of adults with low-grade isthmic slip.¹³ If conservative measures fail to control low back and or leg pain, operative treatment may be indicated.^4,¹⁴

OPTIONS FOR SURGICAL MANAGEMENT

In general, the surgical options in the management of spondylolysis and spondylolisthesis are as follows: pars repair, neural decompression without or with stabilization, and fusion (without or with decompression). Spinal fusion can be approached with various techniques: (1) posterolateral in situ fusion with or without instrumentation, (2) circumferential in situ fusion (anterior interbody or posterior interbody fusion), (3) slip reduction and posterolateral fusion or circumferential procedures with or without sacral dome resection, and (4) in spondyloptosis slip reduction or L5 excision and fusion of L4 to the sacrum.

Spondylolysis: pars repair

A direct repair of a pars defect, which is in essence a stress fracture, is a logical operative solution in patients with symptomatic spondylolysis. Repair of the pars restores normal anatomy, without loss of segmental motion, and does not require an extensive surgery since fusion is avoided.¹⁵ It may also reduce mechanical stress on the adjacent spinal levels. A prerequisite for the procedure is the presence of a type IIA pars defect¹ and a nondysplastic posterior arch, together with a normal disc and facet joints at the involved level. To better delineate which patients are suitable candidates for pars repair, lidocaine infiltration of the pars under fluoroscopy may be helpful. Postinjection pain relief and the presence of a pars defect smaller than 7 mm, are the best predictors for clinical success of this surgical procedure.^15,¹⁶ Pars repair can also be considered in individuals with a minimal slip without disc degeneration.

There are several operative methods available to achieve this goal. The most commonly used techniques are Buck’s screw fixation,¹⁷ Scott’s transverse process wiring,¹⁸ or Morscher’s hook screw device.¹⁹ Biomechanical testing has demonstrated that pars screws or devices that rely on pedicle screw fixation provide better mechanical stability and minimize stress across the pars defect.²⁰ In all pars repair techniques the need to excise the pars pseudoarthrosis, freshen the bone edges, and to apply locally cancellous bone graft is of utmost importance. A brace is worn after surgery for at least 8–12 weeks.

Bradford and Iza ¹⁸ reported on their experience with the Scott’s wiring technique in 22 patients. They found that the clinical outcome of the Scott’s wiring was favorable in 80% of the patients, and 90% obtained a pars defect fusion. Johnson and Thompson²¹ found that the clinical outcome of the Scott’s wiring was favorable in individuals with spondylolysis younger than 25 years of age. Buck reported on his experience with the Buck screw in 75 patients. The surgical outcome was good in 88%.¹⁷ Hefti et al.¹⁹ reported on their experience with the Morscher hook screw technique for direct repair of the pars in 33 patients. Pain relief was attained in 79% of patients and a healed pars was observed in 73%. The largest series of patients with pars repair published to date included 113 individuals who underwent pars repair with the Morscher device and were followed for an average of 11 years.¹⁶ Union of the pars defect was achieved in 87%. Pseudoarthrosis rates were found to be four times higher in patients older than 20.¹⁶

Decompression in isthmic and dysplastic spondylolisthesis

When radicular pain, as opposed to back pain, is the main complain of the patient, even in the absence of neurological deficit, neural decompression may be in indicated. Gill ²² suggested removing the loose posterior elements and the fibrocartilagenous pars defect in order to decompress the neural elements without performing arthrodesis, and argued that this was the management of choice for symptomatic spondylolisthesis. He indeed published a report of a series of patients in whom pain alleviation was achieved with laminectomy alone, without arthrodesis. However, when one considers that spondylolisthesis is by definition an unstable condition, surgical damage to the posterior ligamentous structures by performing a laminectomy will render the spine even more unstable. Indeed, Gill himself noted some increase in the amount of vertebral slip in about 40% of his patients. Others have documented a more pronounced postoperative slip progression following laminectomy without fusion, not only in children and adolescents but also in young adults under the age of 40.^8,^11,^23,²⁴ Gill’s laminectomy, when performed alone, is mentioned only to be condemned, especially in children and adolescents. Carragee considers it futile performing decompressive laminectomy in adults with mild isthmic slip without neurological signs as it does not improve the clinical outcome and may increase the rate of pseudoarthrosis following noninstrumented spondylodesis.⁵ Combining decompressive laminectomy with pedicular screw fixation will provide better clinical results.⁵ Carragee’s experience echoes earlier reports that decompression is not always mandatory in patients with radicular pain. Posterolateral fusion alone will often eliminate radicular symptoms.^25,²⁶ The absolute indications for decompression in spondylolisthesis are: symptomatic radiculopathy with motor deficit, or sphincteric involvement.

While isthmic spondylolisthesis is a pathological condition in which ‘canal expansion’ is the rule (as the loose lamina remains behind the slipped body), dysplastic spondylolisthesis is a pathological condition that leads to significant spinal canal stenosis (the lamina remains intact and by slipping forward constricts the cauda equina). Therefore, in cases of symptomatic, dysplastic spondylolisthesis with a forward slip greater than 25%, a laminectomy should always be performed.

Posterolateral in situ fusion

In low-grade olisthesis

For more than five decades in situ posterolateral fusion with iliac crest bone graft was the most commonly applied surgical procedure for low-grade isthmic spondylolisthesis and is considered even today as the gold standard, especially in children and adolescents.²⁴ Although anatomical reduction of the slip may be desirable, restoration of function with minimal risk to the patient is the ultimate goal of surgery in spondylolisthesis. In low-grade slips in situ arthrodesis carries a minimal risk, and leads to good or excellent clinical results in most patients. Reports on the successes of in situ posterolateral monosegmental fusion with or without Gill’s decompression date back to the late 1950s and early 1960s.^27,²⁸ Two retrospective studies reviewed almost 300 patients, and reported greater than 80% fusion rates and a clinically asymptomatic postoperative result.^27,²⁸

Wiltse and Jackson ⁸ popularized the paraspinal approach for in situ arthrodesis. The procedure is carried out through a midline skin incision, followed by bilateral incision of the thoracolumbar fascia and bilateral muscle splitting through the sacrospinalis with exposure of the lateral gutters and the transverse processes. Arthrodesis extends from the transverse processes of L5 to the sacral alae. Autologous iliac crest bone graft is laid down. The results of in situ fusion are good to excellent in most cases with fusion rates of 68–100%.^8,²⁹^–³¹ Postoperative management may include cast or brace immobilization, although many surgeons do not apply postoperative immobilization at all.^8,³¹ Postoperative immobilization may be recommended if decompression was performed in addition to the spondylodesis or in patients with slips greater than Meyerding 2. Decompression should be performed in conjunction with arthrodesis whenever a focal neural deficit correlating with the spinal imaging is present.¹¹ It was already noted that some surgeons^8,^25,²⁶ do not perform decompression in conjunction with arthrodesis in both adolescents and adults, as in situ fusion alone was found to eliminate neurologic symptoms.

In general, the results obtained in adults with in situ fusion are not as good as in children and adolescents,³²^–³⁴ not only because of the associated degenerative changes which may be present above and at the slip level, but also due to smoking status and workmen’s compensation claims.³³ Haraldsson and Wilner³⁴ conducted a comparative study of posterolateral fusion in adolescents and adults and noted that only 57% of adults with a lumbosacral slip who underwent fusion had a good clinical result as opposed to the 95% successes rate obtained in children and adolescents. In contrast to the different clinical outcome observed in the two groups, fusion rates approached 100% in both adolescents and adults.³⁴ More recently, and in considerable contrast to the last three cited reports,³²^–³⁴ Moller and Hedlund⁴ reported a high success rate of in situ fusion in adults with low-grade slips. One hundred and eleven patients were randomly allocated to either an exercise program or posterolateral fusion. At a minimum 2-year follow-up, patients subjected to surgical fusion had statistically superior results on both the Disability Rating Index and the visual analog scale.⁴ Moller and Hedlund⁴ concluded that posterolateral fusion is a method supported by evidence-based medicine standards to reduce back pain and functional disability in adult isthmic spondylolisthesis. They also reported that the results of noninstrumented fusion were as good as those attained with instrumentation¹⁴ The clinical results obtained by Moller and Hedlund are even more striking since Gill’s decompression was carried out in two-thirds of the patients (all with sciatic pain) in both the noninstrumented and instrumented groups (personal communication). This author’s own personal experience with decompression and fusion in adult isthmic spondylolisthesis is similar.³⁵ Between January 1999 and July 2003, 25 consecutive adults with symptomatic lumbosacral isthmic slip (average age 50 years) underwent surgery for slips ranging from grade 1 to 4. All cases had a Gill procedure, instrumentation, and posterolateral fusion (Fig. 100.1).³⁵ Back and leg pain relief was achieved in all with radiological evidence of solid fusion. The results of fusion surgery in adults with isthmic spondylolisthesis are certainly better than those observed in adults undergoing fusion for purely degenerative disc disease.³⁶ The combination of mechanical instability associated with spondylolisthesis, compounded by the development of degenerative changes with or without neural compression, will respond more favorably to spondylodesis.¹³

Fig. 100.1 (A) Lateral X-ray of the lumbosacral junction of a 58-year-old female, taken 8 years after in situ instrumentation and fusion of a grade 2+ isthmic spondylolisthesis. (B) Anteroposterior X-ray of the same patient. Note the solid posterolateral L5–S1 fusion.

In high-grade olisthesis

In situ fusion is not only efficient in low-grade olisthesis but also in patients with high-grade slips. Because the transverse process of L5 may be dysplastic and small and lies too deep to be accessed, in situ fusion of high-grade slips may extend from the ala to the transverse process of L4. Postoperative immobilization in high-grade slips is mandatory. Casting or bracing with thigh extension (in one leg) should be instituted for a least 2–3 months. Johnson and Kirwan ³⁷ collected 17 patients with slips greater than 50% managed by in situ fusion. Sixteen of the 17 patients had a good clinical result. Reynolds and Wiltse published a similar-sized series and similar success rate.³⁸ No change was observed in the degree of slip or sagittal rotation at the final follow-up X-ray.³⁸ These authors noticed that with the attainment of a solid fusion (approximately 7 months postoperatively), pain, hamstring tightness, overall cosmetic appearance, and posture were improved. Peek et al.²⁵ reviewed eight adults with grade 3 and 4 slips, who were managed by in situ fusion without decompression. Again, good results were recorded in all patients, including resolution of neural deficits, even though no neural decompression was performed. Boxall et al. also reported that pain, gait abnormalities, hamstring tightness, and neural deficit all resolve with in situ fusion without concomitant decompression.¹² Seitsalo et al.³⁹ collected 93 adolescents (mean age 14.8 years) who underwent surgery for high-grade spondylolisthesis with long-term follow-up. Ninety-four percent of the patients obtained satisfactory clinical results with in situ fusion only. Another study from the same institution found that in situ fusion results in adolescents compared favorably with the results of surgical slip reduction accompanied by both anterior and posterior fusion; however, in the latter group postoperative complications were more common.⁴⁰

Drawbacks of in situ fusion in high-grade slips

Despite the impressive excellent functional results obtained with bilateral lateral in situ fusion, there are several drawbacks with this technique when managing high-grade slips. In high-grade slips, the fusion mass is subjected to tension, flexion, and shearing forces. Attaining a solid fusion can be endangered by repetitive stress fractures in the fusion mass leading to gradual slip progression. Indeed, some authors report a high incidence of pseudoarthrosis (up to 45%) in patients with high-grade slips undergoing in situ arthrodesis.^11,^12,^39,⁴¹^–⁴³ In addition, an increase in the slip angle (15–20 degrees) and the degree of slip (up to 33% increase) were noted as well despite an apparently solid fusion mass.^12,^41,⁴² Slip progression was found to occur in the first 6 months after surgery. Although in situ fusion is considered a simple and safe surgical technique, neural injury is possible. Schoenecker et al.⁴⁴ collected 189 patients who underwent in situ fusion for high-grade slip at several major US spine centers. Twelve of them (6%) developed cauda equina symptoms following in situ fusion. In less than 50% of these patients did the cauda equina injury recover. Patients at risk for developing postoperative cauda equina dysfunction were those with slip angles greater than 45 degrees. Schoenecker⁴⁴ postulated that the cauda equina injury was probably the result of intraoperative slip progression that occurred due to loss of muscle protection during anesthesia as well as the surgical destabilizing effect. Radiculopathy of the first two sacral roots is common before surgery in many patients with high-grade slips. This is explained by the fact that the S1 and S2 roots tent over the vertical sacrum. In addition, in many of the patients there is also evidence for L5 radiculopathy. The likelihood for intraoperative neural injury in high-grade slips is thus compounded.