The viscoelastic responses of the human cervical spine in torsion: experimental limitations of quasi-linear theory, and a method for reducing these effects.

The dynamic torsional viscoelastic responses of the human cadaver cervical spine were measured in vitro. The quasi-linear formulation of time dependent behavior was used to describe and predict the resultant torque as a function of applied angular deflection and time. The performance of the quasi-linear model was good, reaching correlation at the 99% confidence level; however, it tended to underestimate hysteresis energy (mean relative deviation = -19.1%) and observed stiffness. This was in part due to difficulties in establishing the physical constants of the quasi-linear model from finite rate relaxation testing. An extrapolation deconvolution technique to enhance the experimentally derived constants was developed, to reduce the detrimental effects of finite rate testing. The quasi-linear model based on this enhanced derivation showed improved predictive ability and hysteresis energy determination.