[A biomechanical study of the lumbar intervertebral disc by the finite element method].

The biomechanical characteristics of the lumbar intervertebral disc were investigated by 3-dimensional finite element method. The results were: (1) Under compression load, the nucleus pulposus received the strongest vertical force and the annulus fibrosus restrained its expansion. The inner posterolateral annulus fibrosus was vulnerable. (2) Under flexion load, some posterior shifting of the nucleus pulposus occurred, along with the decrease of posterior bulging and the increase of anterior bulging. The outer anterior and inner posterior annulus fibrosus were vulnerable. (3) Under either compression or flexion load, the increase in the nucleus pressure ratio (PN/Pa) for the same disc attained almost the same value. (4) At the nucleus area ratio of 37.5%, the maximum compressive stiffness value occurred. (5) PN/Pa decreased with the increase of the nucleus area ratio but increased as disc narrowing advanced. (6) When the nucleus pulposus lost its hydrostatic property, the compressive stiffness value decreased to 43%, the potential damage could encompass the entire annulus fibrosus.