Spinal deformity and back surface asymmetry in idiopathic scoliosis.

Stereo radiography and stereotopography were used to record simultaneously the three-dimensional spinal and back surface shape of 141 patients with a clinical diagnosis of adolescent onset idiopathic scoliosis. Radiography confirmed 80 patients with single lateral curves (Cobb angle 5-87 degrees); 59 with double curves (Cobb angle 5-61 degrees), and two patients with triple curves. Orientation of each vertebra was measured by the lateral deviation from the spinal axis and the axial rotation. For each curve detected, the Cobb angle, the maximum deviation, the maximum axial rotation, and the sagittal plane curvature was measured. Topographic data were used to generate a profile of a cross-section through the back of each vertebral level. This section was characterized by its axial rotation, deviation of its midpoint from the spinal axis, and area symmetry about the midpoint. Maximum values of these measurements in the region of each radiographic scoliosis curve were noted. Regression and correlation analysis showed (for each curve) a high correlation of apical vertebral lateral deviation with back surface axial rotation (r = 0.79) and with vertebral axial rotation (r = 0.79). The back surface rotation was less than vertebral rotation in magnitude, however, by a mean factor of 0.55. The measurement of the back surface asymmetry that gave the highest correlation with the skeletal deformity was the axial rotation. Relationships between skeletal and surface measures were similar for curves in thoracic and lumbar regions and for patients with single and double curves. There is potential for clinical application of surface measurement techniques to prescription of orthoses and monitoring of changes due to progression or treatment.