The mechanics of prolapsed intervertebral disc.

Cadaveric lumbar intervertebral joints were subjected to compressive loads while wedged in forward flexion. In some specimens disc lesions were produced and we have been able to identify three different types: postero-lateral radial fissure, annular protrusion and nuclear extrusion. The type of lesion depended on the loading regime but all occurred more readily in slightly degenerated discs.