Degenerative Spondylolisthesis—What We Know, What We Don’t, and Where We Go From Here

Adam M Pearson
US Musculoskeletal Review, 2011;6(1):39-41
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Abstract

The evidence base supporting the treatment of degenerative spondylolisthesis (DS) has improved markedly over the past 20 years; however, there is still a need to determine whether fusion is indicated for all patients and what type of fusion is the most appropriate. Here, I review what is known, and what still needs to be determined, about the treatment of DS.
Keywords
Degenerative spondylolisthesis, fusion, evidence-based medicine
Disclosure The author has no conflicts of interests to declare.
Received: April 15, 2011 Accepted May 10, 2011
Correspondence: Adam M Pearson, MD, MS, Dartmouth-Hitchcock Medical Center, 1 Medical Center Drive, Lebanon, NH 03756. E: adam.pearson@hitchcock.org

Degenerative spondylolisthesis (DS) is a common condition in our aging population, affecting up to 30% of osteoporotic women over 65 years of age.1 It is also the most common diagnosis leading to fusion in the Medicare population, a procedure that is being performed more frequently and at highly variable rates across the US.2,3 The combination of an aging population and the use of more expensive technology to perform lumbar fusion will lead to increasing costs associated with the treatment of DS and a greater degree of scrutiny over the indications for surgery and for various methods of fusion in this patient population. As such, the spine community must be able to provide evidence supporting the treatment protocols for DS. Previously, patients with DS were categorized as a subgroup within spinal stenosis (SpS); however, recent evidence from the Spine patient outcomes research trial (SPORT) has demonstrated that patients with DS are treated with fusion more frequently and have better surgical outcomes compared with patients with SpS.4 As such, future studies need to focus specifically on the DS population to better define the indications for surgery, the appropriate surgical techniques, and expected outcomes for this condition. In this article, I evaluate critically where we stand in answering the following questions about DS: is either surgery or a non-operative treatment favored for this condition; is fusion indicated in DS; what type of fusion leads to the best outcomes; and what factors predict surgical and non-operative outcomes?

Surgical versus Non-operative Treatment
Two large-scale trials comparing surgery with non-operative treatment for SpS included patients with DS and demonstrated an advantage for surgery for the combined SpS—DS cohort.5–8 These trials did not perform subgroup analyses specifically on the patients with DS. As such, SPORT is the only large-scale trial to compare surgery with non-operative treatment in a well-defined DS population.3,9 Although SPORT was initially designed to include both a randomized clinical trial (RCT) and observational cohort, within four years of the trial starting, 54% of patients randomized to non-operative treatment had undergone surgery, and 36% of patients randomized to surgery did not undergo surgery. Owing to this high rate of cross-over, a meaningful intention to treat analysis of the RCT was not possible; therefore, the randomized and observational cohorts were combined in a statistically controlled as-treated analysis.10 The results of these analyses demonstrated a clear advantage to surgery on all of the main outcome measures, including the Short Form 36 (SF-36) bodily pain (BP) and physical function (PF) scores and the Oswestry Disability Index (ODI), out to four years. These results must be viewed in the context of the inclusion criteria, which included neurogenic claudication or radicular pain for at least 12 weeks, neurologic findings on physical examination, and imaging demonstrating spinal stenosis with a degenerative listhesis. The results are not generalizable to patients with a shorter duration of symptoms or with only axial low back pain.

Critics of SPORT pointed out that the as-treated analysis did not provide level I evidence demonstrating the superiority of surgical treatment, because the results could be confounded by unmeasured variables that could not be controlled for in the analysis.11 This is a valid criticism, and the high level of cross-over in SPORT demonstrated the challenges inherent in a study comparing surgery with non-operative treatment for a condition in which patients experience primarily pain. It appears that the only way to perform a RCT comparing surgery to non-operative treatment successfully would be to restrict patients from crossing over—a study design that would encounter serious ethical and logistical problems—or use a sham surgery control group—a study design that would probably have Given these limitations, the SPORT data might be the best evidence generated to determine whether surgery or non-operative treatment leads to better outcomes in DS. As such, most experts now agree that surgery leads to better short- and medium-term outcomes in patients with DS who have symptoms lasting at least three months.

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