Immediate spinal and paraspinal muscle responses to Schroth Method exercises in adolescent idiopathic scoliosis: a real-time three-dimensional ultrasonography study

To quantify immediate, real-time changes in three-dimensional spinal alignment and paravertebral muscle parameters during the performance of a single Schroth posture using three-dimensional ultrasonography.This study further aimed to provide an objective, real-time assessment of skeletal and muscle responses during Schroth performance, which is traditionally guided by therapist palpation and visual inspection. Forty participants with adolescent idiopathic scoliosis (AIS) classified as 3 C (3-curve) or 4 C (4-curve double) with Cobb angles of 20°-45° were enrolled (20 per group). Four Schroth Method postures (self-corrective sitting, self-corrective standing, door handle exercise, and muscle cylinder) were each compared with the habitual posture.Paravertebral muscle volume was measured at the upper end vertebrae (UEV), apex vertebrae (AV), and lower end vertebrae (LEV). Three-dimensional ultrasound parameters included the ultrasound curve angle (UCA), thoracic spinous process angle (TSPA), lumbar spinous process angle (LSPA), thoracic axial vertebral rotation (TAVR), and lumbar axial vertebral rotation (LAVR). The study included 40 participants (20 per group). Across both 3 C and 4 C groups, all four corrective postures significantly reduced UCA and LSPA compared with habitual posture (all p < 0.05). In 3 C group, self-corrective sitting, door handle exercise, and muscle cylinder improved TAVR ( p < 0.01; p < 0.01; p = 0.02). Muscle volume increased with self-corrective standing (concave AV, UEV; p < 0.01), muscle cylinder (bilateral all regions; p < 0.05), and door handle exercise (concave AV, p = 0.02; LEV, p = 0.04; bilateral UEV, p < 0.01). In 4 C group, all postures improved LAVR ( p < 0.001); self-corrective sitting and door handle exercise also improved TAVR ( p = 0.02; p < 0.001), while muscle cylinder improved TSPA ( p < 0.01). Muscle volume increased with door handle exercise (concave UEV in thoracic; concave AV, bilateral LEV in lumbar; all p ≤ 0.05) and muscle cylinder (concave AV in thoracic; concave AV, bilateral LEV in lumbar; all p ≤ 0.05), whereas it decreased with self-corrective sitting (convex AV, bilateral UEV in thoracic curve; concave AV in lumbar curve; all p ≤ 0.01). In this preliminary study of a single Schroth corrective posture, three-dimensional spinal alignment demonstrated immediate posture-specific changes, accompanied by region- and side-specific paravertebral muscle volume responses. These findings provide objective insight into the acute biomechanical effects of Schroth exercises and support further investigation of individualized exercise strategies using longitudinal designs. The study protocol was prospectively registered at ‘Chinese Clinical Trial Registry’ under the trial identifier ChiCTR1800018310, dated 11/09/2018.