One of the most important problems in biomechanics is the determination of the structural properties of the major load-bearing parts of the human body. Damage to these load-bearing areas constitutes a serious public health problem. In order to better understand these structural properties, the passive bending responses of the human spinal column were investigated using whole cervical and lumbar spines obtained from unembalmed cadavers. These specimens were placed in a state of eccentric axial load by an electro-hydraulic test apparatus. Eight channels of force, moment, and deformation data were recorded during a battery of tests designed to measure the time-dependent structural properties of the specimens. Stiffness was measured in six bending modes. Viscoelastic responses studied included relaxation of moment, cyclic conditioning effects, and pseudoelastic moment-angle behavior. After the battery of viscoelastic tests were performed, a series of ramp-to-failure tests was run on all cervical and lumbar spines, with conditions of restraint at the specimen ends that were designed to simulate the in vivo mechanical environment. This was done in order to determine the effect of various end conditions on the mode of failure of the specimens. Specimen damage was documented through both radiological techniques and dissection.

Results included the short- and long-time stiffnesses of the cervical spine in six bending modes, and those of the lumbar spine in four sagittal-plane bending modes. An estimate of the damping was also reported for each bending mode. In addition, both the cervical and the lumbar spine bending responses were modeled using a quasilinear viscoelastic beam model. For each bending mode, the geometrically-normalized bending responses were pooled, and an average moment-angle response function was generated. These models were found to be good predictors of spinal bending responses to a wide variety of input angular-displacement histories. Finally, the results of the failure tests showed that the end conditions had a strong effect on the mode of failure, because they determined the extent to which moments and shear forces act to damage a spine under combined bending and axial loads.