Biomechanical Comparison between Artificial Disc and Lumbar Interbody Fusion Devices

Spinal diseases become more and more serious and dangerous for human population. These deseases cost large medical resources, and add huge encumbrances for our society. Lumbar interbody fusion procedure is an effective technique for treating degenerative spinal instability for the time being, and its final goal is to reduce the patient’s low back pain. However, the fusion procedure frequently associated with postoperative long-term complication of junctional degeneration, resulting in the cause of one more operation. Therefore, newer artificial disc is developed to overcome the disadvantage of fusion procedure. However, although the artificial disc could provide the range of motion similar to the healthy spinal disc, severe complications such as implant dislocation, implant subsidence, implant metal plate failure and facet joint arthrosis might occur from time to time. The purpose of this study is thus to compare the biomechanics different between artificial disc and spinal fusion procedure and offer better solution to the spinal operation. This study adopted a five-level spinal ligamentous finite element model that has been valided by stiffness test. To create this model, computed tomography (CT) scans of the lumbar spine from L1-L5 of a healthy young male were obtained. The commercially available finite element program ANSYS was then used to model the spinal segments such as cortical bone, cancellous bone and posterior element from these scanned images. In addition, the solid model for the artificial disc, BAK cage will be created with the SolidWork 2004 CAD software, and these solid models will be combined to the five-level spinal ligamentous finite element model. To place the artificial disc and BAK cage in the position of L4-L5, the standard clinical surgical procedure will be followed in the simulation. Totally five models will be created, such as intact lumbar spine, anterior lumbar interbody fusion with BAK, anterior lumbar interbody fusion with carbon fiber cage, artificial disc replacement with Charit`e III in the lumbar spine and artificial disc replacement with ProDisc II in the lumbar spine. In these models, the inferior surface of the L5 vertebral body will be constrained completely. The loading conditions will include 10Nm bending moments on flexion, extension, torsion and lateral directions respectively, and preload of 150 N on the superior surfaces of the L1 vertebral body. The biomechanics parameters considered for this research will include the range of motion, maximum stress of the adjacent level body and soft tissue (L3-L4), maximum contact pressure of the facet joint on surgical level, maximum tensile force of the posterior ligaments, the stress distribution on the artificial disc and the stress distribution of the whole lumbar spine. By understanding the biomechanical differences in treating the degenerative spinal instability between artificial disc and spinal interbody fusion device, we expect to design improved devices through the help of optimization technique.

Project ID:PB9408-0521
External Project ID:NSC94-2320-B182-054