Changes in range of motion, intradiscal pressure, and facet joint force after intervertebral disc and facet joint degeneration in the cervical spine

Degeneration of the intervertebral discs and facet joints is considered a source of pain in the cervical spine. In this study, we developed finite element models of cervical spines that were healthy or had various extents of degeneration and investigated changes in biomechanical behaviors of the cervical spine, such as range of motion (ROM), intradiscal pressure, and facet joint forces. Degenerative changes associated with mild, moderate, and severe degeneration of the disc and facet joint were described at the C5-C6 motion segment unit (MSU). With progression of degeneration, intersegmental ROM decreased at the degenerated MSU but increased at the healthy MSUs, intradiscal pressure decreased at the degenerated MSU but only slightly changed at the healthy MSUs, and facet joint forces at both degenerated and healthy MSUs increased. These findings could be used to understand the mechanisms underlying injury of the cervical spine caused by disc and facet joint degeneration.