Background <p>Adolescent idiopathic scoliosis (AIS) can be associated with restrictive lung disease. Brace wearing is also associated with restrictive lung disease. Due to external compression, bracing could alter the biomechanical function of the rib cage. The aim of this work was to test the feasibility of using biplanar radiography to study the impact of the brace on the rib cage kinematics during breathing.</p> Materials and methods <p>Twelve patients with moderate AIS, treated with Cheneau-Toulouse-Munster (CTM) brace, underwent pulmonary function test and biplanar radiography at two lung volumes: normal breathing and full inspiration with and without brace. Their spine and rib cage were reconstructed in 3D from the radiographs.</p> Results <p>Lung volumes were reduced after application of the brace, both by pulmonary function test and 3D reconstruction. The reduction in the rib cage volume appeared to be due to changes in rib cage width, in relation to the pressure pads. Costo-vertebral strategy did not seem to be modified by brace wearing. The brace tended to increase the correction of the cobb angle in maximum inspiration.</p> Conclusions <p>This study confirms the relevance of assessing respiratory function using biplanar radiography and 3D reconstruction. By reducing lung volumes without changing the costo-vertebral strategy, the impact of the Cheneau brace on ventilation remains to be clarified.</p> Level of evidence <p>III, prospective.</p>