The Nonlinear Load-Displacement Response of the Human Annulus Fibrosus in Axial Tension and Compression: Finite Element Predictions

To elucidate the pathomechanics of intervertebral disc degeneration, finite element models (FEM) have been developed to identify the regions of the disc most susceptible to mechanical failure (Shirazi-Adl et al, 1984). However, these models have only been validated using load-displacement data obtained from whole motion segments. Since the gross deformation of a motion segment is dependent on several tissues within this complex composite structure, models developed solely using this technique may not accurately predict stress and strain within specific subregions of the disc. To address this problem, an experimental protocol has been developed to directly test the annulus fibrosus in axial tension and compression (Lotz and Ashford, 1994). This experimental model eliminates the confounding effects of the nucleus pulposus, cancellous bone and endplate, and hence serves as a basis for validation and refinement of a FEM of the annulus. The objective of this study was to develop a FEM of an 8 mm circumferential segment of the human annulus fibrosus. The load-displacement response of this model in axial tension and compression was compared directly with experimental results (Lotz and Ashford, 1994).