High-frequency ultrasonography in quantifying paraspinal muscle remodeling after Schroth therapy for adolescent idiopathic scoliosis: a retrospective observational study

This retrospective observational study quantitatively assessed paraspinal muscle structural changes following Schroth therapy in patients with Adolescent Idiopathic Scoliosis (AIS) using high-frequency musculoskeletal ultrasound (HF-MSKUS), with the aim of characterizing short-term morphological adaptations associated with this standardized intervention. Fifty AIS patients completed 12 weeks of Schroth training (January 2024–January 2025). Inclusion criteria included AIS (Cobb angle > 10°) with an apical vertebra between T10–L2. HF-MSKUS measured bilateral transverse diameter (TD), anteroposterior diameter (APD), perimeter (P), and cross-sectional area (CSA) at the upper-end, apical, and lower-end vertebral levels before and after training. Prior to treatment, typical muscular asymmetry was observed, characterized by relative convex-side atrophy and compensatory hypertrophy on the concave side. Following Schroth training, significant pre–post changes in paraspinal muscle morphology were detected at all measured levels. At the upper-end vertebra, convex-side TD, APD, P, and CSA increased significantly after intervention (all p < 0.001). At the apical vertebra, convex-side CSA showed a significant increase (ΔCSA ≈ + 0.53 mm², p < 0.01), whereas concave-side CSA decreased significantly (ΔCSA ≈ − 0.44 mm², p < 0.01), indicating a redistribution of bilateral paraspinal muscle morphology. At the lower-end vertebra, convex-side CSA increased (ΔCSA ≈ + 0.51 mm²) and concave-side CSA showed a mild reduction (ΔCSA ≈ − 0.44 mm²), with statistically significant pre–post differences (p < 0.01).In severity-based subgroup analyses, significant pre–post changes in paraspinal muscle morphology were observed within both mild and moderate–severe groups. However, due to the limited sample size in the moderate–severe subgroup, quantitative comparisons between severity strata should be interpreted cautiously. HF-MSKUS proved to be a feasible, radiation-free modality for serial assessment of paraspinal muscle structure in AIS. These findings demonstrate measurable short-term morphological adaptations of the paraspinal muscles following 12 weeks of Schroth therapy, while the functional significance and long-term clinical implications of these changes warrant further investigation.