Dorso-lumbar junction: biomechanical role of mamillaris processus and transversospinales muscles

Abstract

The dorso-lumbar junction is a very important limit between areas where vertebrae have very different morphology and therefore function. Everyone stresses the shape and the orientation of articular faces in the dorsal and lumbar spine. In the dorsal spine, the instant rotation centres of the articular processes are in the middle of the intervertebral disc, which makes rotation easier. At the lumbar level, the instant rotation centres project themselves on the spinous process more or less near its extremity. In the lumbar moving segments there are thus two rotation centres, the first corresponding to discal rotation, the second to rotation of articular facets. Rotation is only possible by a clipping movement inside the disc. However, the lumbar spine is the privileged site of flexion extension, due to the thickness of the disc being greater at this level. The morphological transition may be only on one vertebra, usually T12, or on two or three.