Finite element analysis of anterior cervical spine interbody fusion.

The present study investigated the external and the internal biomechanical responses of anterior cervical discectomy coupled with fusion. Five different types of interbody fusion materials were used: titanium core, titanium cage, tricortical iliac crest, tantalum core, and tantalum cage. Two different types of surgical procedures were analyzed: Smith-Robinson and Bailey-Badgley. A validated three-dimensional anatomically accurate finite element model of the human cervical spine was used in the study. The finite element model was exercised in compression, flexion, extension, and lateral bending for the intact case and for the two surgical procedures with five implant materials. The external response in terms of the stiffness and angular rotation, and the internal response in terms of the disc and the vertebral stresses were determined. The Smith-Robinson technique resulted in the highest increase in external response under all modes of loading for all implant materials. In contrast, the Bailey-Badgley technique produced a higher increase in the disc and the vertebral body stresses than the Smith-Robinson technique. As experimental human cadaver tests can only determine the external response of the non-fused spine simulating immediate post-operative structure, the present finite element studies assist in the understanding of biomechanics of interbody fusion by delineating the changes in the extrinsic and intrinsic characteristics of the cervical spine components due to surgery.