Section 15, Chapter 3: Treatment of Degenerative Spondylolisthesis

Peter Försth and Helena Brisby

NON-OPERATIVE TREATMENT

There is strong evidence for the use of surgery in the treatment of lumbar spinal stenosis (LSS) with or without degenerative spondylolisthesis (DS).^1-4 However, a conservative approach for up to 6 months can be recommended as there is a chance of spontaneous improvement and a possibility for the patient to recognize and accept the symptoms.⁵ A slip is not to be considered an indication for surgery and there are now several studies demonstrating that patients with lumbar problems from degenerative changes do not have more pain or discomfort if DS is present.^6-9 The risk of sudden deterioration is very low and disastrous results from a non-surgical approach are seldom observed.¹⁰ The natural course of untreated DS has been reported to be benign and the progression of slip and clinical symptoms does not correlate.¹¹ Clear guidance in the literature on efficient non-operative treatment options are lacking.¹² However, there is some evidence that Gabapentin might have a positive effect on walking capacity and pain.¹³ Epidural steroid injections have been frequently used, especially in the US, but there is no robust evidence for its use.¹⁴ Physical activity in general and especially with the lumbar spine in a flexed position (which relieves pressure on the neural structures) like pole walking or bicycling might be beneficial and increase general health and function. A recent study in Sweden showed improvement of pain and function and a 50% reduction in the desire for surgery in a group of LSS patients who trained regularly on a stationary bicycle for 4 months.¹⁵

SURGICAL TREATMENT

Indications for surgery are: severe problems from the classical symptoms of LSS with neurogenic claudication, limitation of physical function (especially walking capacity), failed non-operative treatment and the very rare condition of rapidly developing severe neurologic deficits with symptoms of cauda equina syndrome. However, the patient’s general condition and comorbidities must be taken in consideration in elderly patients. The basic surgical principles of treatment of DS are the same as for the treatment of LSS without DS, i.e., to relieve compression on neural structures in the spinal canal. In a minority of cases there might be a risk of postoperative instability and in these patients a concomitant fusion might be warranted. The hypothesis that patients with LSS might suffer from instability after decompression has been suggested by several authors.^16-19 This has led many spine surgeons to conclude that fusion is beneficial when decompression is performed. The presence of pre-operative DS has often been associated with “instability,” a term that today is not clearly defined and explained. There has been a frequent use of flexion/extension X-ray to investigate whether there is instability in DS patients. Many surgeons define instability as a difference in slip of ≥ 3 mm between flexion and extension views. However, there is no clear correlation between movement on flexion/extension X-ray and disability or pain. Further, this method is associated with measurement errors (up to 4 mm) and there is no general agreement on a normal pattern or range of sagittal plane movements in the lumbar spines of healthy subjects.²⁰ The method is also dependent on the patient’s pain status and cooperation. Finally, the repeatability is low.²¹ In the award winning biomechanical study by Shaffer, et al., it was concluded that the use of flexion/extension X-rays to diagnose instability can lead to serious errors in classification unless the observed translation exceeds 5 mm.²² There has been a widespread use of fusion in combination with decompression in LSS/DS patients who, in addition to pseudoclaudicatio (the main reason for decompressive surgery), suffer from notable back pain. In several studies, however, improvement of back pain has been at the same level as the improvement of leg pain after decompressive surgery without fusion.^8,9,23-25 Improvement of back pain after decompression alone has been shown regardless of whether DS was present pre-operatively. Furthermore, pre-operative DS is not associated with a higher level of preoperative back pain when compared to patients without a slip, a finding now reported in several studies.^6-9 We conclude that the importance of pre-operative DS appears to be overestimated.

Decompression Technique

As for LSS without DS, there are several approaches to reach the spinal canal to decompress the neural structures. The classic laminectomy nowadays most often is performed with a less invasive technique than some decades ago when surgery for spinal stenosis began to spread. With a central approach with resection of the midline structures, the osteophytes from the medial part of the facet joint can be removed with a chisel, Kerrison or burr at an angle more perpendicular to the joint surface than when the approach is lateral of the midline structures. This enables preservation of as much as possible of the facet joint, which is probably the most important structure for the stability of the segment.²⁶ The stabilizing role of the midline structures in a lumbar segment has been much debated and minimally invasive techniques to preserve these structures have been developed in the last decade. However, the evidence for the creation of instability after decompression with removal of the midline structures is weak and many of the biomechanical studies promoting preservation of midline structures were done in vitro and, in best case, on lumbar segments from human cadavers, but in many cases on porcine segments. Thus, the application on the erect human degenerative spine is questionable.

In a randomized comparison of unilateral laminotomy, bilateral laminotomy and laminectomy, Thomé et al. found superior clinical outcomes after using midline preserving techniques.²⁷ However, in a recent register study from Norway on 885 patients, no differences could be found between microdecompressive surgery with preservation of the midline structures compared to laminectomy.²⁸ This was also the conclusion reached in a recent Cochrane review on the effectiveness of minimally invasive posterior decompression techniques compared with conventional laminectomy.²⁹ In summary, the review found low or very low evidence for the superior effect of unilateral laminotomy for bilateral decompression, bilateral laminotomy and split-spinous process laminotomy compared with conventional laminectomy. No advantages for the microdecompressive techniques were found regarding complications, length of the procedure, length of hospital stay or post-operative walking ability when compared with laminectomy.²⁹ In a radiologic biomechanical pilot study, the authors used the three-dimensional CT technique to measure translation and rotation in vivo before and after decompression in patients with LSS and DS.³⁰ The 20 patients included in this pilot study were randomly assigned to either central decompression with removal of the midline structures (laminectomy) or bilateral foraminotomies with preservation of the interspinous ligament. The findings indicated a minimal increase in movement at maximum provocation in extension and flexion 6 months after surgery. Mean increase in 3D translation was 0.63 mm and in 3D rotation 0.47 degrees. Removal of the midline structures did not result in a significant increase in instability as compared with preservation of these structures. Although the study was not powered to draw any conclusions on differences in clinical results regarding the removal and preservation of the midline structures, there was significant improvement in all studied patient-reported outcome measures 1 and 2 years after surgery for both groups.

A possible explanation of the preserved segmental stability in our study and the fact that DS patients in many clinical studies do well after decompression alone despite removal of stabilizing structures, is that in vivo remaining interspinal structures and (with time) scarring tissue play a stabilizing role. In contrast to isthmic spondylolisthesis, the degree of slip in DS is limited by the articular processes and is usually of grade I and more seldom of grade II according to the Meyerding classification (see Figure 2-3 in Section 15 Chapter 2). Also, the fact that the disc in a DS segment usually has considerably degenerative changes and loss of height might contribute to stability.³¹ These factors might contribute to the post-operative segmental stiffness after a joint preserving technique for decompression and explain why large slippages after decompression are rare.

The Role of Fusion

During the last few decades the use of fusion in LSS patients with DS has been considered as almost mandatory by the majority of surgeons in order to avoid possible post-operative increased instability and restenosis. In the US, 96% of patients with DS undergo a fusion procedure as an adjunct to decompression.³² The works by Herkowitz and Kurz¹⁸ from 1991 and Bridwell, et al.³³ from 1993 have been the main basis for this routine. However, although these studies have been reported as RCTs and thereby with a high degree of evidence, their status as such has been questioned because of the overall design and lack of validated outcome measures.^34-36 Studies of observational design that promote fusion have also had limited validity because of flawed data reporting and small groups of patients.^35,37,38

In an observational study of 213 patients from the Spine Tango Register, Kleinstueck, et al. reported better results when fusion was added to decompression in LSS with DS.³⁹ The authors compared decompression alone with decompression and concomitant fusion and used evaluation of back and leg pain as outcome measures. The reduction of back pain was greater after fusion, but because the fused patients had more back pain pre-operatively, the level of back pain was equal in the two treatment groups at a 1-year follow-up.³⁹

In an RCT published in NEJM 2016 containing 66 patients with single level DS, Ghogawala et al. found a better outcome with fusion compared to decompression alone two years after surgery.⁴⁰ The primary outcome measure, SF-36 Physical-Component Summary, showed an advantage for the fusion group with an improvement of 15.2 points compared to 9.5 points for the decompression alone group. The difference of 5.7 points was significant (p = 0.046) but close to the minimal clinically important difference of 5 points described for this outcome measure. For the Oswestry Disability Index (ODI), which was chosen as a secondary outcome measure, there was no difference between the treatments. Also, in the SF-36 components of Physical Function, Bodily Pain and Vitality there were no differences. Further, conclusions from this study are hampered by a high dropout rate (14%) and the substantial difference in reoperations between the treatment groups. Thirthy-four percent in the decompression alone group vs. 14% in the fusion group had a reoperation within 4 years. The substantially higher reoperation rate during follow-up in the decompression-alone group could negatively affect the results of the SF-36 assessment of overall well-being during the recovery period. Moreover, differences in reoperation rates cannot be considered as a validated outcome measure as a subsequent surgery is an event that may be performed for a number of reasons and is not solely the choice of the patient. The threshold for performing a reoperation in an unsatisfied patient is probably lower when only one treatment option remains (i.e., fusion surgery), especially when clinical instability is considered to be an important indication for surgery.⁴⁰

Several observational studies on large cohorts have been published in recent years comparing decompression alone to decompression with fusion in patients treated for LSS with DS. In two studies with data from the Swedish spine register (Swespine) on 1,306⁸ and 1,624²⁵ DS patients, respectively, no benefit was found with the addition of a fusion. The same conclusion was drawn in a Canadian study on 179 patients.⁴¹ Contrary to these results, a recent registry study from Norway on 520 patients demonstrated moderate advantages for the use of fusion surgery in this patient group.⁴²

In the Swedish Spinal Stenosis Study, published in the same issue in NEJM as the Ghogawala et al. paper, a subgroup of 135 patients had DS (mean slip 7.4 mm).⁹ They were randomized to either decompression with concomitant fusion or decompression alone. At follow-up after two years there had been a significant improvement in all outcome measures but no differences were found between the two treatments. This was also true in a subgroup of 69 patients with a slip more than the mean slip of 7.4 mm (7.4–14.3 mm). Ninety-one of the patients were operated upon due to a single level spondylolisthesis like in the study by Ghogawala et al., without differences between the treatment groups. Also, among the 66% of the patients that had passed five years post-op there were no differences in results. With a mean follow-up of 6.5 years, 21% of the decompressions and 22% of the fusions had undergone subsequent surgery.⁹

In health economic evaluations, the use of fusion has been found to add significant costs to treatment compared to decompression alone, but without advantage in cost-benefit analyses.^9,43,44 In the Swedish Spinal Stenosis Study, the addition of fusion was 6,800 USD more costly per patient compared to decompression alone.⁹ Health economic analysis from the SPORT trial revealed an increase in cost with 20,967 USD in patients where a fusion was added compared to decompression alone.^43,44 Thus, limiting the fusion rate could substantially reduce costs without sacrificing quality. Apart from the lower treatment cost for each patient, the use of decompression without fusion can also save resources by releasing capacity in the operating theatre and the post-operative ward through shorter surgery time and hospital stay. This would be of particular benefit in communities with over-stretched public medical services that produce long queues for medical treatments.

Fusion surgery is associated with an increased risk of severe complications in elderly patients. A large analysis of registry data showed that the addition of fusion surgery to decompression surgery doubled the risk of severe adverse events and was associated with an absolute risk difference that corresponded to a number needed to harm of 30 treated patients.^45,46 A study from the Spine Tango Register also revealed higher proportions of both surgical and general complications after decompression with fusion, compared to decompression alone.⁴⁷ These facts need to be taken into consideration in the decision-making for type of surgery.

SUMMARY

Clearly there are some patients with DS that have a risk to develop instability and inferior results from decompression alone. However, there is no evidence that fusion in general benefits the overall group of DS patients. On the contrary, the higher risk of complications, higher costs and the lack of superiority with fusion should make surgeons hesitate to use this treatment. Patients where the addition of a fusion should be considered are patients with clinically relevant foraminal stenosis, where nerve root symptoms correlate to the level of root compression. In these patients, it might be difficult to decompress without removal of the articular processes posteriorly in the neuro-foramina, which might cause progression of a slip. Also, preoperative radiological findings of sagittal oriented facet joints and preserved disc height have been proposed to predict instability after decompression.³¹ These are circumstances where the addition of a fusion might be beneficial. However, there is a need to further develop radiologic tools to detect patients at risk for developing instability after decompression.

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