Multimodal quantitative characterization and mechanistic exploration of paraspinal muscle groups in adolescent idiopathic scoliosis.

BACKGROUND: The mechanical properties of muscles and their interactions with three-dimensional spinal deformities are difficult to quantify with a single method. This study aimed to quantitatively characterize the paraspinal muscle groups in adolescent idiopathic scoliosis (AIS) using multimodal methods. METHODS: The patients with AIS who received corrective surgery at our hospital from June 1, 2025, to August 31, 2025 were enrolled in this prospective study. Two independent evaluators used 3.0T magnetic resonance imaging (MRI) and digital radiography (DR) to analyze parameters in the bilateral paraspinal muscle groups. RESULTS: This study enrolled 25 patients with AIS, including 15 cases with lumbar curvature and 10 with thoracic curvature. There were significant differences in the multimodal quantitative characterization of the convex and concave sides of scoliosis in AIS patients (p < 0.05). On the concave sides of the lumbar curvature, the erector spinae, multifidus muscles and psoas major muscles showed a higher fat fraction, higher signal intensity, and smaller volume than those on the convex sides. The erector spinae muscle was significantly thicker on the concave side in lumbar curvature, and on the convex side in thoracic curvature. Two evaluators showed good intra- and inter-observer consistency, with intraclass correlation coefficients (ICC) ranging from 0.75 to 0.85. The Cobb angle showed almost no correlation with the flexibility index on the concave side. For cases of thoracic curvature, the maximum vertebral inclination angle showed a strong positive correlation with the erector spinae thickness ratio on the convex side (r = 0.85). CONCLUSION: The quantitative assessment results of this exploratory study using MRI and DR methods showed that muscle asymmetry in the paraspinal muscles may interact with three-dimensional spinal deformity in patients with AIS.