Preoperative Leg Muscle Quality Association Functional Recovery After Adult Spinal Deformity Surgery: A Propensity-Score-Matched Study

<i>Background and Objectives:</i> We conducted a retrospective observational study. <i>Background:</i> While traditional rehabilitation approaches emphasize trunk muscle conditioning, emerging evidence suggests that leg muscle strength plays a critical role in postoperative functional mobility. Previous studies have focused on trunk muscle rehabilitation in patients with adult spinal deformity (ASD). However, recent findings suggest that leg muscle conditioning may be a better predictor of postoperative improvement. Strengthening the gluteal and iliopsoas muscles has been linked to improved sagittal balance, gait stability, and mobility, ultimately leading to enhanced surgical outcomes. This study examines the relationship between the preoperative functional cross-sectional area (FCSA) of trunk and leg muscles and postoperative improvement in mobility, as assessed by the Timed Up and Go (TUG) test, in patients undergoing surgery for ASD. <i>Materials and Methods:</i> Sixty-two patients (57 women, mean age 71.2 ± 7.1 years) who underwent ASD surgery between April 2017 and April 2024 were retrospectively analyzed. The FCSA of key muscles-psoas major (PM), erector spinae (ES), multifidus (MF), gluteus maximus (GM), and gluteus medius (GMed)-was measured using CT images. Patients were categorized into an improvement group and a non-improvement group based on whether they achieved the minimum clinically important difference (MCID) of -2 s in the TUG test 12 months after surgery. Propensity score matching (PSM) was applied to adjust for baseline differences between the groups. A significance level of 5% was used for all comparisons. <i>Results:</i> Thirty-three patients achieved a clinically meaningful improvement in TUG, while 29 did not. Before PSM, patients with worse preoperative TUG and Oswestry Disability Index (ODI) scores showed greater improvements (<i>p</i> < 0.01). After PSM, no significant differences were found between the groups in terms of age, sex, or BMI. However, the improvement group showed significantly greater FCSA values in PM (6.1 ± 2.3 mm² vs. 3.9 ± 1.5 mm², <i>p</i> = 0.021) and GM (19.9 ± 5.9 mm² vs. 15.3 ± 3.9 mm², <i>p</i> = 0.019). <i>Conclusions:</i> This study demonstrates that leg muscle quality, particularly that of the gluteus maximus and psoas major, is a significant predictor of postoperative mobility improvement in patients with ASD. These findings challenge the conventional focus on trunk muscles and suggest the inclusion of leg muscle training in preoperative rehabilitation strategies to enhance surgical outcomes.