The effect of soft tissue properties on overall biomechanical response of a human lumbar motion segment: a preliminary finite element study

This study investigates the relative effect of soft tissue properties on the overall response of a human spinal motion segment using an osseo-ligamentous FE model of the Visible Man L3-L4 intervertebral joint. Model geometry was obtained from the Visible Man CT dataset using custom built image processing software. Non-linear soft tissue properties were obtained from the literature. Displacement controlled simulations were performed in flexion, extension, lateral bending and axial rotation. The effect of each soft tissue structure (including the annular fibres) was assessed by removing it from the model and comparing the predicted overall stiffness to that of the intact segment. The results from this study showed that removal of the capsular ligaments and the collagen fibres in the annulus of the intervertebral disc have the largest effects on the overall stiffness of the motion segment. All other ligament structures had little impact on determining the motion response, with the exception of the anterior longitudinal ligament. Its removal caused the stiffness in extension to fall to 60 percent of the value reached for the intact model. It is concluded that correct representation of the mechanical properties of both the capsular ligament and annular fibres is most important in generating realistic FE models of the lumbar spine to predict motion segment biomechanics.