Biomechanical comparison of effects of the Dynesys and Coflex dynamic stabilization systems on range of motion and loading characteristics in the lumbar spine: a finite element study

Background The primary purpose of dynamic stabilization is to preserve the normal range of motion (ROM) by restricting abnormal movement in the spine. Our aim was to analyze the effects of two different dynamic stabilization systems using finite element modeling (FEM). Methods Coflex and Dynesys dynamic devices were modeled and implanted at the L4-L5 segment using virtual FEM. A 400N compressive force combined with 6N flexion, extension, bending and axial rotation forces was applied to the L3-4 and L4-5 segments. ROM and disc loading forces were analyzed. Results Both systems reduced ROM and disc loading forces at the implanted lumbar segment, with the exception of the Coflex interspinous device, which increased ROM by 19% and did not change disc-loading forces in flexion. Conclusions The Coflex device prevented excessive disc loading, but increased ROM abnormally in flexion. Neither device provided satisfactory motion preservation or load sharing in other directions. Copyright (C) 2015 John Wiley & Sons, Ltd.