Effects of trunk position on back surface-contour measured by raster stereophotography.

A study of the contour of the surface of the back was conducted using the Quantec spinal image system (QSIS; raster stereophotography) and the Vicon 3-dimensional (3-D) motion analysis system with a plaster model of the scoliotic spine. With postural changes in 3 dimensions came alterations in the surface shape of the back. Most changes in QSIS parameters occurred in the coronal plane. The study showed that model 1, with 9 degrees of Q angle (similar to Cobb angle in the coronal plane) in right thoracolumbar scoliosis, altered 3-D metrics less than model 2 did, with 54 degrees of Q angle in scoliosis. The change in the position of the trunk in the transverse plane had a more significant impact on the QSIS parameters. Raster stereophotography has been used clinically to monitor curve progression. Changes in transverse rotation of the trunk correlate significantly with variations in Q angle and axial rotation. Clinicians using a raster stereophotograph system to assess scoliotic deformity need to control postural sway, as doing so results in more stable and reproducible measurements that can be used for clinical follow-up.