Measurement of human lumbar spine ligaments during loaded and unloaded motion

Length changes in the ligaments of human lumbar spine motion segments were investigated in order to find conditions under which unusual stress or stress reduction is found in the longitudinal ligaments and facet joint capsules. Flexibility measurements were performed under load. Increasing load and height reduction in the motion segment increases the flexibility. The anterior and posterior longitudinal ligament normally operate in the elastic part of their stress-strain curve. Destruction of the intervertebral disc leads to a dislocation of the centers of rotation in the motion segment. Two types of facet joint capsules were observed. Height reduction in the motion segment leads to abnormal strains in one type sooner than in the other, which can be normalized by slight flexion. Injection of a silicone compound into the disc normalizes many of the changes in the motion segment due to height reduction.