Biomechanical effects of the CoflexTM implantation on the lumbar spine. A nonlinear finite element analysis

OBJECTIVE: To evaluate the effect of the stabilization of the CoflexTM device on the biomechanical behavior of the instrumented and adjacent spinal segments.

METHODS: The study was carried out at the Department of Orthopedics, Shanghai Institute of Traumatology and Orthopedics, Ruijin Hospital, Shanghai, China between September 2009 and May 2010. Upon validation, a finite element model of L3-S1 segment was developed to simulate and analyze the biomechanics of the intact and CoflexTM implanted states subjected to simulate loading of flexion, extension, lateral bending, and axial rotation.

RESULTS: This study predicted that the segmental motion, intradiscal pressure, and facet contact force at the levels adjacent to the CoflexTM implanted level were not significantly affected by the implantation of CoflexTM device. There was a significant decrease in range of motion in extension at the instrumented level of the CoflexTM implanted model relative to the intact model. Furthermore, the level implanted with CoflexTM device showed a significant decrease in intradiscal pressure in extension and a decrease in facet contact force in extended, lateral bending and axial rotational conditions, compared with the intact model.

CONCLUSION: This study suggests that the CoflexTM device has the potential of effectively unloading the disc in extension and the facet joints in extension, lateral bending, and axial rotation at the CoflexTM implanted level, without deleterious effects on the adjacent segments under the simulated physiological condition.