Application of the maximum energy criterion to describe the strength of the motion segment under axial compression.

Abstract

A simulation study of compression of vertebral motion segments to failure was performed. The aim of this study was to determine whether damage of the motion segment under axial compression can be predicted when the load is quantified by means of the elastic energy storage it causes in the segment. Although in one-cycle loading, motion segment strength can be described by the relationship between the product of the bone density and cross-sectional area of the vertebrae and the maximum force, no single criterion has been found to describe strength in both one-cycle and cyclic compressional loading protocols. Input data were derived from in vitro studies by Hansson et al, Keller et al, and by Brinckmann et al. Elastic energy storage at failure was computed using a three-parameter model for a viscoelastic solid with a nonlinear initial response, and related to the product of the bone density and cross-sectional area. The relationship of the product of density and area with the elastic energy appeared to be accurately described by a curvilinear equation. This relationship accounted for 65-93% of the variance in maximum energy. Generalizability of the relationship from cyclic axial loading to one-cycle axial loading was successfully tested. The results of the present study have shown that one criterion suffices to describe the strength of the motion segment in different compressional loading modes.