Cervical injuries under flexion and compression loading.

Cervical spine segmental tests were performed to determine the specific patterns of initial cervical injury in response to loading just beyond the point of structural failure. Well-defined combinations of flexion rotation and compression translation were applied to segments with varying degrees of disc and facet degeneration. Twelve cervical spine specimens (from human cadavers ages 52-91 years), each consisting of three vertebrae (two motion segments) from the middle (C2-C5) or lower (C5-T1) regions, were subjected to pure flexion rotation (seven specimens) or to combined flexion rotation and axial compression translation (five specimens). Specimens were sectioned and dissected to determine the patterns of structural failure. Pure flexion, and combined flexion and compression produced similar patterns of injuries. The disc was the most commonly injured structure, with annular injuries noted in 8 of the 12 specimens, and with anterior herniation of the nucleus occurring in two specimens. Wedge fractures and posterior ligament injuries were noted in both specimen groups and with both modes of loading. We conclude that similar patterns of initial anterior bony compressive failure and posterior ligamentous failure can occur with both flexion and with combined flexion-compression, without axial or lateral rotation, at low rates of loading. Anterior cervical disc herniations were produced in both middle and lower cervical segments.