Preoperative Vertical Instability May Predict Below-Average Outcomes After Lumbar Decompression Surgery for Spondylolisthesis with Stenosis

Introduction: Several research groups have concluded that decompression alone can yield outcomes comparable to decompression and fusion for degenerative spondylolisthesis with stenosis, and that improved guidelines are needed to determine which surgical option is best for each patient. We hypothesize that retrospective analysis of data from a prospective study on the role of translational instability in surgical planning may provide insight into additional variables, beyond translational instability, that could influence surgical outcomes.

Methods: Preoperative flexion-extension radiographs for 48 patients from a previously reported prospective study were analyzed using automated, FDA-cleared methods. In addition to translational instability, we measured vertical instability using a standardized metric. Based on prior research, if this metric is greater than 2, it is considered abnormal. Data were analyzed using threshold-limit graphs and standard statistical tests to assess the potential for predicting ODI scores, leg/buttock pain, and patient satisfaction.

Results: Patients with a vertical instability metric greater than 3 (15/48 patients), had significantly less improvement in ODI scores (12 points versus 25 points, P=0.02) and less improvement in NRS leg/buttock pain (2.2 points versus 4.1 points, P=0.06). Additionally, only 33% of patients with a vertical instability metric greater than 3 were satisfied with decompression surgery, compared to 76% satisfaction among patients when the metric was less than 3 (P=0.005).

Conclusion : Translational instability is commonly used as the primary radiographic metric to determine whether fusion is needed in addition to decompression for lumbar spondylolisthesis with stenosis. This post hoc analysis of data from a previously published prospective study suggests that, in addition to translational instability, the presence of vertical instability may also predict below-average outcomes in patients with degenerative spondylolisthesis and stenosis treated using decompression alone. Additional research is required to determine if the findings can be repeated and have prospective clinical efficacy.