Load Distribution in Functional Spinal Unit with SB Charite III(R) Artificial Disc; Finite Element Analysis

ABSTRACT

OBJECTIVE: To evaluate the effects of SB Charite III(R) artificial disc implantation on the biomechanics of functional spinal units. METHODS: A nonlinear intact osteoligamentous three-dimensional finite element model of L4-L5 was developed using 1-mm CT scan data from a human volunteer, and the material properties of each element were determined. The model was validated using biomechanical data. A model that was implanted with SB Charite III(R) artificial discs via an anterior approach was also developed. The stresses and strains of the vertebral bodies and surrounding spinal ligaments were investigated. The implanted model was compared to the intact model in terms of range of motion, force on facet joints with flexion-extension, lateral bending, and axial rotation under 400 N preloading. RESULTS: There were no significant differences between the findings of this finite element study and other reports in the literature. Our analytical method proved useful method for the biomechanical evaluation of the effects of artificial disc implantation. The implanted model revealed an increased range of motion in flexion-extension, lateral bending, and axial rotation compared to the intact model. The stresses on facets were greater in the implanted model than in the intact model. CONCLUSION: The model that was implanted with artificial discs showed increased segmental motion and stress on the facet joints compared to the intact model. We hypothesize that the removal of the anterior longitudinal ligament is the major cause of increased segmental motion and stress on the facet joints in the implanted model. The development of new artificial discs should focus on compensating for these unwanted results.