Introduction: In the surgical treatment of neurogenic claudication and/or radiculopathy in isthmic spondylolisthesis it is debatable whether instrumented fusion (DF) has to be added to decompression (D). To that end a randomized controlled trial was performed randomizing patients to both treatment options, and the two year analysis demonstrated a superior outcome for DF. Eligible patients that declined randomization were included in an observational cohort study. The objective of the current study is to analyze this larger population, to assess a possible difference in outcome between randomized and patient-preferred treatment, and to evaluate whether a subgroup of patients would benefit more of a particular treatment strategy.

Methods: Between 2008–2017, 172 patients with low-graded isthmic spondylolisthesis enrolled in this study (84 in RCT) and were followed up for 2 years. Primary outcome measures were Roland Disability Questionnaire and patient’s perceived recovery. Visual-analogue scale (VAS) for back pain and for leg pain, and the proportion of reoperated patients were evaluated as secondary outcome measures through Kaplan-Meier analyses. Repeated-measurement analysis of variance was performed. Subgroup analyses were performed for gender, age, BMI, smoking, patient preference, and DF after D.

Results: 85 patients received decompression-alone (D), and 87 patients received decompression-and-fusion (DF). Both groups were similar at baseline. At 12-week follow-up, improvement of Roland Disability Questionnaire scores were comparable (D: 5.1 points 95% CI [3.7 to 6.5] and DF: 6.6 points 95% CI [5.3 to 8.0], p = 0.38). In contrast, both VAS back pain (25.5 points 95% CI [18.6 to 32.3] in D versus 35.9 points 95% CI [29.1 to 42.6], p = 0.034) and leg pain (23.5 points 95% CI [13.3 to 33.7] in D versus 34.0 points 95% CI [24.1 to 43.8], p = 0.04) improved significantly more in the DF-group.

At 2-year follow-up, DF-group showed 4.1 points more improvement in RDQ scores (9.8 95% CI [8.3 to 11.4] versus 5.7 95% CI [4.1 to 7.3], (p < 0.001), and more improvement in VAS-back pain (-17.4 (95% CI [-27.2 to -7.5] p = 0.001). VAS-leg pain did not differ between both groups (p = 0.1). Perceived recovery was comparable in both groups at 12-week follow-up (37% (D) versus 58.3% (DF; p = 0.08), but superior for DF (74% versus 47.1%; p < 0.001) at 2-year follow-up. None of the subgroup analysis demonstrated a superior outcome for mere decompression. During the 2-year follow-up period, cumulative probability of reoperation was 38.6% in the D-group and 6.2% in the DF-group (p < 0.001). RDQ score was significantly worse in patients that were submitted to DF after D (Figure 1).

Discussion: In patients with isthmic spondylolisthesis, decompression and instrumented fusion showed superior functional outcome and perceived recovery compared to decompression-alone at two-year follow-up. Additionally, decompression and fusion resulted in less reoperations, and adding fusion to decompression in second stage led to inferior functional outcome. No subgroups could be discerned to have a better outcome with mere decompression. Therefore, we recommend decompression and instrumented fusion over decompression-alone as a primary surgical treatment option in isthmic spondylolisthesis.