Are coupled rotations in the lumbar spine largely due to the osseoligamentous anatomy?

Abstract

Previous studies have found that primary rotations in the lumbar spine are accompanied by coupled out-of-plane rotations. However, it is not clear whether this accompanying rotation is due to passive (discs, ligaments and facet joints) or active (muscles) spinal anatomy. The aim of this study was to use a finite element model of the lumbar spine to determine three-dimensional rotations in the loaded spine, due to passive spinal anatomy alone.

The observed similarity between computed and in vivo nucleus pressures and primary rotations at each spinal level provide confidence in the models' ability to predict the passive mechanics of the osseoligamentous lumbar spine. Coupled rotations due to primary motions in the sagittal and transverse planes appear to be caused by the passive spinal anatomy. However, for lateral bending, data for the computed coupled rotations suggest that the passive anatomy alone does not account for the observed coupled rotation in vivo, and we hypothesize that the muscles play a key role in the coupled response of the spine under this motion.