Strength and motion analysis of the human head-neck complex

This study was conducted to correlate the pathology of the experimentally tested human cervical spine with biomechanical strength information and localized temporal movements of the various spinal components. Eight fresh human cadaveric head-neck complexes were subjected to compressive forces at a quasistatic rate of 2.5 mm/s until failure. Biomechanical force and deflection data were collected. Localized kinematic data as a function of time were obtained from retroreflective targets placed in the anterior and posterior regions of the vertebral body, facet column, and spinous process at every level of the cervical spine. The specimens were radiographed prior to, during, and following failure; they were then deep frozen at the level of failure to preserve the localized tissue deformations. Specimens underwent computed tomography scanning and sequential sectioning using a cryomicrotome. The failure forces and compressions ranged from 1.3 to 3.6 kN and 0.9 to 3.7 cm. Stiffness and energy-absorbing characteristics ranged from 96.1 to 220.5 kN/m and 12.2 to 53.6 J, respectively. Varying localized temporal motions among spinal components were found to exist at all levels of the head-neck complex. With increasing compressive loads, the specimen components reorient as demonstrated by kinematic changes in the spinal elements; failure was imminent when the structure no longer resisted any further increase in external load. The study demonstrated that an evaluation of the human head-neck complex in a relaxed state, as in clinical observations on posttraumatic radiographs, is often different from that documented immediately following the traumatic insult; this underscores the importance of conducting controlled in vitro investigations to determine the injury biomechanics of the human cervical spine.