Study design: A new type of composite device with a similar structure to a natural lumbar intervertebral disc was modeled, and its mechanical interaction with a L3-L5 lumbar spine segment was studied by a finite element analysis.
Objective: To identify the influence of the prosthesis on the biomechanical changes induced in a L3-L4 lumbar spine segment model after having substituted the physiologic L4-L5 intervertebral disc by the implant.
Summary of background data: In our societies, the large number of back pain cases highly motivates the investigation of intervertebral disc prostheses. Postoperative complications induced by spinal fusion showed that the mechanical properties of the novel components and its interactivity with the rest of the spine are a critical point.
Methods: The prosthesis replaced the L4-L5 intervertebral disc within a previously developed L3-L5 lumbar spine segment physiologic model. The effect of loads in compression, flexion, extension, and axial rotation was simulated, and two types of vertebrae-implant contact were compared to the physiologic model.
Results: Models with disc substitute are much stiffer than the physiologic model. In case of perfect contact with the adjacent vertebrae, the implant behaves like a physiologic intervertebral disc and respects the surrounding motion segment biomechanics. Although no traumatic loads were calculated within the adjacent vertebrae, bone remodeling would be expected in the trabecular bone.
Conclusion: By using numerical methods, this study allows prediction of the static mechanical behavior of a new device within a lumbar spine structure, which appears very useful for preclinical study.