Bi-planar spinal stereoradiography of adolescent idiopathic scoliosis: considerations in 3D alignment and functional balance

A prospective, cross-sectional study to determine the impact of arm position on the 3D spine and pelvic parameters and postural balance in adolescent idiopathic scoliosis. A total number of 37 adolescent idiopathic scoliosis patients were enrolled prospectively. Three arm positions, (1) 45A degrees shoulder flexion with knuckles on clavicles, (2) 90A degrees shoulder and elbow flexion with forearms and palms on the front wall, and (3) arms hanging on either side, were instructed to the cohort. Bi-planar low dose X-ray images of the spine and pelvis were registered in a stereoradiography system in the first and second arm positions. A pressure mat recorded the position of the center of pressure in each arm position. Spinal and pelvic parameters were measured for the cohort. Statistical analysis was performed to determine the agreement between the spinal and pelvic parameters and standing balance in different arm positions. Thoracic kyphosis, sacral slope, sagittal vertical axis, T1 tilt, and spinal height were significantly different between the knuckles on clavicle and forearms on the wall positions p < 0.05. Significant differences were observed in the pressure distribution under the feet between the wall and freestanding positions. Bland-Altman plots determined disagreements between the first and second arm positions in clinical measurements and postural assessment of adolescent idiopathic scoliosis. The knuckles on clavicles position replicates the functional standing balance in AIS. Significant differences between the spinal and pelvic parameters suggest that the wall and clavicle arm positions should not be used interchangeably in AIS postural assessment. Diagnostic level II.