Biomechanical effect after Coflex and Coflex rivet implantation for segmental instability at surgical and adjacent segments: a finite element analysis.

The Coflex device may provide stability to the surgical segment in extension but does not restore stability in other motion. Recently, a modified version called the Coflex rivet has been developed. The effects of Coflex and Coflex rivet implantation on the adjacent segments are still not clear; therefore, the purpose of this study was to investigate the biomechanical differences between Coflex and Coflex rivet implantation by using finite element analyses. The results show that the Coflex implantation can provide stability in extension, lateral bending, and axial rotation at the surgical segment, and it had no influence at adjacent segments except for extension. The Coflex rivet implantation can provide stability in all motions and reduce disc annulus stress at the surgical segment. Therefore, the higher range of motion and stress induced by the Coflex rivet at both adjacent discs may result in adjacent segment degeneration in flexion and extension.