Lumbar Muscle Morphology Correlates With Early Surgical Outcomes in Adolescent Idiopathic Scoliosis: A Pilot Study

Study Design Original Research. Objectives This study aimed to evaluate the preoperative cross-sectional area (CSA) and muscle quality of the major lumbar muscles in patients with adolescent idiopathic scoliosis (AIS) and to investigate their associations with perioperative outcomes. The study also explored lumbar muscle morphology as a potential imaging-based surrogate marker for perioperative risk stratification. Materials and Methods In this retrospective study, 81 consecutive AIS patients who underwent posterior spinal fusion at a single institution between January 2019 and December 2023 were included. Two trained pediatric radiologists independently reviewed preoperative T1-weighted axial MRI scans at the L3 level to assess muscle CSA, Modified Goutallier grade, and threshold-based parameters of fatty infiltration. Interobserver reliability was evaluated using intraclass correlation coefficients. Multivariable linear regression analyses were performed to assess associations between muscle parameters and perioperative outcomes, adjusting for relevant covariates. Receiver operating characteristic (ROC) analysis was used to identify curve-specific muscle thresholds for perioperative risk stratification ( P < .05). Results Patients were stratified according to Lenke type: 1-2 (Group 1, n = 30), 5 (Group 2, n = 14), and 3-4-6 (Group 3, n = 37). Fatty infiltration of the multifidus and erector spinae muscles was significantly higher in Groups 2 and 3 compared with Group 1 ( P < .05). Associations between muscle morphology and perioperative outcomes were curve-pattern dependent, with no significant correlations in Group 1. In Group 2, larger functional CSA of the multifidus, paraspinal muscles, and quadratus lumborum was independently associated with increased blood loss (β = 98.06, P = .001; β = 17.49, P = .017; β = 29.3, P = .014). Greater psoas fatty infiltration predicted delayed ambulation (β = 0.236, P = .005). In Group 3, increased paraspinal fatty degeneration predicted longer operative duration (β = 8.42, P = .015). ROC analysis identified curve-specific MRI-derived thresholds for perioperative risk stratification. Conclusion Preoperative lumbar muscle quality, rather than muscle size, was associated with perioperative complexity and recovery in AIS surgery in a curve-pattern–dependent manner. MRI-based muscle assessment may represent a potential tool for perioperative risk stratification, although prospective validation is required.