Sagittal alignment and thoracic cage parameters are correlated with the surgery success rate and life quality of adolescents with idiopathic scoliosis (AIS). However, the effects of the long-term bracing on sagittal and thoracic cage parameters have not been clearly recognized.

Long-term brace treatment could compromise sagittal balance and thoracic development in patients with AIS.

Two hundred and seventy-five patients with AIS were included in this study. The radiographs when AIS was diagnosed and 2 years after Chêneau bracing treatment were collected. Sagittal, cervical, pelvic, and thoracic cage parameters were evaluated. In addition, 32 patients finishing brace treatment with complete radiograph data were selected from included 275 patients and the data of CL, TK and LL at five different time points was collected.

CL (average: from 14.13° to 8.94°, p=0.012), TK (average: from 24.35° to 19.02°, p=0.001) and LL (average: from 38.44° to 32.13°, p=0.004) underwent observably decline after two-year brace treatment. No statistically significant alteration of pelvic parameters was shown. The vertical parameters of thoracic cage including T1–12 height, left and right thorax height and thoracic transverse diameter increased significantly. Thoracic anteroposterior diameter at the T7 vertebral level (average: from 11.49 to 10.57cm, p=0.001) and diaphragm level (average: from 11.89 to 10.74cm, p=0.001) decreased significantly after bracing.

CL, TK and LL decreased after long-term bracing treatment, which lead to the aggravation of “flat back” in AIS patients. In addition, the thoracic anteroposterior diameters declined after two-year bracing, which may result from reduced TK and contribute to further pulmonary function impairment.

IV.