Facet Joint Opening on Computed Tomography Is a Predictor of Poor Clinical Outcomes After Minimally Invasive Decompression Surgery for Lumbar Spinal Stenosis

STUDY DESIGN: Retrospective longitudinal cohort study. OBJECTIVE: To investigate the impact of facet joint opening (FJO) on clinical outcomes after minimally invasive decompression surgery for lumbar spinal stenosis. SUMMARY OF BACKGROUND DATA: Although FJOs have previously been identified as indicators of segmental spinal instability, their impact on clinical outcomes after decompression alone surgery has yet to be investigated. METHODS: This study included 296 patients from a single institution who underwent minimally invasive surgery for lumbar spinal stenosis and were followed up for ≥5 years. Our analysis focused on identifying FJOs at the index decompression level (d-FJO) and at multiple levels (m-FJO) (i.e., ≥3 levels within the lumbar segment) using preoperative computed tomography. Clinical outcomes including reoperations, improvement ratio for Japanese Orthopaedic Association score, and achievement of a minimal clinically important difference in visual analogue scale scores for low back pain or leg pain at 5 years were compared between patients with and without d-FJO or m-FJO. RESULTS: There were 129 (44%) and 62 (21%) patients with d-FJO (more common with lateral olisthesis) and m-FJO (less common with spondylolisthesis), respectively. Reoperations were more common in patients with d-FJO than in those without (16% vs. 5%). On Cox proportional hazards analysis, d-FJO was identified as a predictor for revision at the index decompression level (hazard ratio 4.04, P = 0.03), whereas m-FJO was a predictor for revision at other lumbar levels (hazard ratio 3.71, P = 0.03). Patients with m-FJO had slightly lower rates of achieving minimal clinically important difference in visual analogue scale scores for low back pain (34% vs. 52%, P = 0.03) and poorer improvement ratio for Japanese Orthopaedic Association scores (74% vs. 80%, P = 0.03) than those without. CONCLUSION: FJO at both index decompression level and multiple level were predictors of poor outcomes; patients with FJOs require careful surgical planning or special follow-up.Level of Evidence: 3.