The Influence of Spine Geometry on the Coupling between Lateral Bending and Axial Rotation

Abstract

A biomechanical model study was undertaken to examine to what extent facet joint orientation and inclination of the motion segments influence the coupling between lateral bending and axial rotation that occurs in the human spine. The results show that there is an opposite influence of the inclination of the motion segments and the orientation of the facet joints on the axial rotation associated with lateral bending. As one moves in a rostrocaudal direction along the spine there is a decrease of the axial rotation associated with lateral bending. At the upper part of the thoracic spine there is a reinforcement of the axial rotation due to the ventrally inclined orientation of the vertebrae. In the lower thoracic and upper lumbar spine the axial rotation during lateral bending will oppose that due to the dorsally inclined orientation of the vertebrae. In a flexed position of the spine, this coupling is stronger than in an extended spine.