Lumbar Multifidus Intramuscular fat Concentrations are Associated With Recovery Following Decompressive Surgery for Lumbar Spinal Stenosis. A Longitudinal Cohort Study With 5-year Follow-up.

Study design: Longitudinal cohort study.

Objective: To explore the association between pre-operative lumbar paraspinal intramuscular fat (IMF) and recovery over a 5-year period following surgical decompression for lumbar spinal stenosis (LSS)-related intermittent neurogenic claudication.

Summary of background data: The literature is inconclusive whether higher IMF concentrations on MRI are related to unfavorable outcomes following lumbar decompressive surgery for intermittent neurogenic claudication due to LSS.

Methods: Patients(N=149) with LSS-related intermittent neurogenic claudication (52% male; mean (SD) age: 65.5 (9.1) years; BMI: 27.9 (4.3)) were included for this study. Pre-operative lumbar paraspinal IMF was quantified and categorized as non-severe (<50%) and severe (≥50%) IMF for each muscle (left and right lumbar multifidus and erector spinae) from axial T2-weighted MRI scans using automated computer-vision models. Logistic regression was used to investigate the association between IMF and global perceived effect as well as surgical success. Linear mixed-effects models were used to assess the difference in the clinical course of leg and back pain and disability between the IMF groups. The models were corrected for potential confounders.

Results: Overall, participants with non-severe IMF in the lumbar multifidus reported a higher percentage of successful recovery (53.7% versus 37.5%) and surgical success (76.5% versus 59.9%) compared to the severe IMF group. This association was not present for erector spinae IMF. After adjusting for the potential confounders, the associations between lumbar multifidus IMF and successful recovery and surgical success remained significant for most timepoints across the 5-year follow-up (Odds ratios: 2.26-7.32, p≤0.049). Patients with non-severe IMF in the right lumbar multifidus experienced less disability (P=0.035). No between-group differences were found for the clinical course of leg and back pain (p≥0.143).

Conclusions: Pre-operative levels of IMF in the lumbar multifidus, but not the erector spinae, were associated with 5-year recovery and success following surgery for LSS-related intermittent neurogenic claudication.