Preoperative erector spinae muscle quality is more important than leg muscle quality for postoperative walking recovery in lumbar spinal stenosis: a retrospective study in Japanese patients

STUDY DESIGN: Retrospective cohort study. PURPOSE: To determine whether preoperative trunk and lower limb muscle quality predicts achievement of the minimal clinically important difference (MCID) in the 6-minute walk distance (6MWD) after lumbar spinal stenosis (LSS) surgery. OVERVIEW OF LITERATURE: LSS commonly causes intermittent claudication and reduced walking ability. Previous studies have suggested that muscle quality affects postoperative recovery, but its association with clinically meaningful improvements in the 6MWD remains unclear. METHODS: This retrospective study included 150 patients aged ≥60 years who underwent decompression or fusion surgery for LSS at Okayama Rosai Hospital between April 2021 and April 2023. Preoperative assessments included demographic and surgical factors, Zurich Claudication Questionnaire (ZCQ) scores, visual analog scale scores, the 6MWD, and computed tomography-based muscle quality. The functional cross-sectional areas of the psoas major, erector spinae (ES), multifidus, gluteus maximus, and gluteus medius were quantified in Hounsfield units. Muscle quality was expressed as the low-attenuation muscle area (LAMA) ratio. Patients were classified according to whether they achieved the MCID (80 m) in the postoperative 6MWD. Logistic regression analyses were used to identify predictors of the achievement of the MCID. RESULTS: Among the 150 patients, 86 (57%) achieved the MCID. Univariate analysis showed that younger age, higher preoperative ZCQ scores, a shorter 6MWD, and lower LAMA ratios of all examined muscles were significantly associated with the achievement of the MCID in postoperative walking ability. In multivariate analysis, younger age (p