Fig. 1.

Rupture of the inferior vertebral endplate was the most common mode of failure amongst tested motion segments. In this disc (2-L56) the inferior vertebral endplate has ruptured near the nucleus/annulus transition zone, allowing nuclear material to enter the inferior vertebral body (asterisks). The dashed line marks the centre of the hole through which the injection screw was inserted. The injected contrast gel (rg) has reached the inner posterior annulus, but has failed to penetrate the disc radially beyond this point, leaving the mid and outer portions of the disc intact. N nucleus, SV superior vertebra, IV inferior vertebra, PL posterior longitudinal ligament