Quantitative Paraspinal Muscle Morphology and Risk of 90-Day Complications After Lumbar Instrumentation Surgery.

STUDY DESIGN: Retrospective cohort study. OBJECTIVE: To investigate the association between paraspinal muscle morphology and postoperative complications after lumbar instrumentation surgery for degenerative lumbar spine disease. SUMMARY OF BACKGROUND DATA: Paraspinal muscle degeneration may influence outcomes after lumbar spine surgery; however, quantitative imaging-based predictors of postoperative complications remain limited. METHODS: In this retrospective cohort study, 89 patients who underwent lumbar instrumentation surgery were analyzed. Paraspinal muscle cross-sectional areas of the multifidus and erector spinae at the L4-L5 level were measured using a region-of-interest technique on preoperative MRI. Muscle ratios, a composite Paraspinal Muscle Index (SMI), and asymmetry indices were calculated. Logistic regression and receiver operating characteristic (ROC) analyses were used to evaluate associations with 90-day postoperative complications. RESULTS: Postoperative complications occurred in 19 patients (21.3%). Patients with complications demonstrated lower mean multifidus ratio (P=0.005), erector spinae ratio (P=0.010), and SMI (P=0.004), whereas multifidus asymmetry was significantly higher (P=0.012). In multivariable analysis, diabetes mellitus and operative time remained independent predictors. The addition of muscle parameters increased model discrimination from AUC 0.771-0.820; however, this improvement did not reach statistical significance (P=0.150). CONCLUSIONS: Reduced paraspinal muscle ratios and increased muscle asymmetry were associated with postoperative complications. Quantitative evaluation of paraspinal muscles on routine MRI may contribute to perioperative risk stratification.