The mechanical function of the lumbar apophyseal joints.

Experiments were carried out on cadaveric lumbar spines to determine the mechanical function of the apophyseal joints. It was found that they resist most of the intervertebral shear force and share in resisting the intervertebral compressive force, but only in lordotic postures. They prevent excessive movement from damaging the discs: the posterior annulus is protected in torsion by the facet surfaces and in flexion by the capsular ligaments.