Impact of psoas major width-defined sarcopenia on postoperative clinical outcomes in patients with osteoporotic lumbar degenerative disease undergoing posterior lumbar interbody fusion: a retrospective cohort study

To investigate whether psoas major width (PMW)-defined sarcopenia (an imaging-based screening surrogate for low muscle mass), measured as the psoas major width on a preoperative lumbar anteroposterior X-ray, independently affects 2‑year clinical and radiographic outcomes in osteoporotic patients who have undergone posterior lumbar interbody fusion (PLIF) for the treatment of lumbar degenerative disease. A retrospective cohort study was conducted on patients who underwent PLIF between March 2021 and May 2023. Sarcopenia was defined on the basis of preoperative PMW measurements from standard lumbar anteroposterior radiographs, and patients were stratified into sarcopenia and nonsarcopenia groups. Perioperative characteristics; serial clinical scores, including the visual analog scale (VAS), Japanese Orthopedic Association (JOA), and Oswestry Disability Index (ODI); and radiographic parameters, such as interbody fusion grades, were compared between groups. Multivariate linear regression and ordinal logistic regression analyses were performed to identify factors associated with 2-year clinical improvement and fusion quality. A total of 87 patients were included (32 with sarcopenia and 55 without sarcopenia). Baseline characteristics were comparable between groups (all P > 0.05). At the 2-year follow-up, the sarcopenia group showed significantly less improvement in VAS score (ΔVAS: 3.09 ± 0.93 vs. 4.33 ± 1.06, P < 0.001) and ODI score (ΔODI: 30.19 ± 2.61 vs. 31.45 ± 2.49, P = 0.027) compared with the nonsarcopenia group. Patient-level worst-grade analysis revealed significantly worse interbody fusion quality in sarcopenic patients ( P = 0.002, linear-by-linear association test). After adjusting for multiple covariates (age, sex, BMI, BMD, operation time, and surgical segments), multivariate regression confirmed that sarcopenia was independently associated with poorer pain improvement (ΔVAS: β = − 1.438, P < 0.001), and was associated with a modest reduction in ODI improvement (ΔODI: β = − 1.899, P = 0.040). Moreover, sarcopenia was associated with a more than sixfold increased risk of inferior fusion quality (OR = 6.68, 95% CI 1.61–27.73, P = 0.009). Preoperative PMW-defined sarcopenia is independently associated with less pain relief and poorer fusion quality, and was associated with a modest reduction in ODI improvement. Nevertheless, both groups achieved clinically meaningful functional recovery. Routine PMW assessment on standard lumbar radiographs may aid preoperative risk stratification.