Fat Infiltration in the Multifidus Muscle as a Predictor of Prognosis After Decompression and Fusion in Patients with Single-Segment Degenerative Lumbar Spinal Stenosis: An Ambispective Cohort Study Based on Propensity Score Matching

OBJECTIVE: To determine whether fat infiltration in the multifidus muscle would predict surgical prognosis in patients with degenerative lumbar spinal stenosis (DLSS). METHODS: This ambispective cohort study enrolled 118 consecutive patients undergoing surgery for 14-5 single-segment DLSS. Fat infiltration rate (FIR) on magnetic resonance images of the multifidus muscle at L5-S1 were measured using ImageJ software. The enrolled patients were divided into FIR <25% and FIR >= 25% groups according to their FIR of the multifidus muscle at L5-S1. The 2 groups of patients who finished follow-up were further matched for the baseline covariates based on propensity scores. Patients' reported outcomes including the visual analog scale score for back pain and leg pain, and the Oswestry Disability Index (ODI) score were compared between groups at follow-up and further adjusted using generalized linear models. RESULTS: Patients in the FIR <25% group showed statistically significantly greater reduction in ODI at 6 and 18 months after surgery than did patients in the FIR >= 25% group in either cohort regardless of adjustment; however, the 2-point between-group difference was smaller than the predefined minimum clinically important difference. In addition, more patients in the FIR <25% group achieved clinically significant improvement in ODI than those in the FIR 25% group in either complete cohort or matching cohort (63.8% vs. 21.1%, P < 0.001; 70.3% vs. 24.1%, P < 0.001, respectively) before and after adjustment (63.3% vs. 27.8%, P < 0.001; 69.1% vs. 31.0%, P < 0.001, respectively). CONCLUSIONS: Fat infiltration in multifidus muscle at L5-S1 could be a potential predictor of functional improvement after surgery in patients with 14-5 single-segment DLSS.