Calibration of the finite element model of a lumbar functional spinal unit using an optimization technique based on differential evolution.

The development of a finite element model of the lumbar spine usually involves choosing among available alternatives to decide which values should be assigned to the material properties of the different spinal structures. Furthermore, the model has to be validated so that a reasonable approximation to the mechanical response of the lumbar spine is achieved. One approach for choosing such material properties involves calibrating the model by choosing the properties that produce the best fit with the in vitro mechanical response of the lumbar spine. This study proposes the use of an optimization method based on differential evolution to calibrate the finite element model of a functional spinal unit. Calibration was performed using reported in vitro data on the mechanical response of an intact lumbar functional unit and its successive reduced stages after the dissection of ligaments, facet joints, vertebral arch and nucleus pulposus. The loading conditions in the study were pure moments in flexion, extension, lateral bending and axial rotation. Considering all dissection stages and loading conditions, the maximum difference in vertebral rotation between the in vitro data and the model results was only 1.24°. Other model results such as facet loads and annulus fibrosus behavior also correlated well with reported data.