Rib movement in health, kyphoscoliosis, and ankylosing spondylitis.

Costal movement was defined on living subjects by determining the spatial vectors along the ribs that are produced during inspiration. The determination of these vectors was achieved with an instrument specially designed for this purpose. Rib movement was studied on 61 ribs in 10 normal subjects and on 35 ribs in six patients suffering from kyphoscoliosis and ankylosing spondylitis. In normal subjects during smooth inspiration all the ribs studied, which ranged from the 2nd to the 9th, rotated round a single axis. The direction of the inspiratory movement of the ribs was oblique, upward, outward, and forward, and symmetrical in both hemithoraces. This direction is compatible with rotation around the rib-neck axis but not with other axes that have been postulated. In ankylosing spondylitis and in kyphoscoliosis the magnitude of rib movement was reduced but movement still took place solely around the rib-neck axis. In the patients with kyphoscoliosis the direction of this movement was altered due to a change in the position of the rib neck.