Biomechanical comparision of coflex and dynesys dinamic stabilization systems with finite element model

IntroductionThe aim of this study is to analyse the effect of dynamic stabilisation systems, Dynesys Dynamic Stabilisation System and Coflex Interspinous Device, which are widely used clinically, to the range of motion and disc load characteristics of lumbar spine biomechanically with finite element method (FEM).Materials and MethodsFirst 3 lumbar vertebrae (L3-L4-L5) are modelled by FEM. Then one Coflex Interspinous Device (Paradigm Spine, LLC, New York, NY) and one Dynesys Dynamic Stabilisation System (Zimmer Spine, İnc., Warsaw, IN) are modelled and implanted virtually at L4-L5 segment of lumbar vertebrae by FEM. Flexion, extansion, bending and rotation forces are applied to this two models and one intact vertebrae model. Range of motion and disc loading forces at L4-L5 level are measured and compared in this three model virtually by FEM.ResultsThe two main findings of this study are : Both systems reduce range of motion and disc loading forces at implanted lumbar segment with one exception seperately. The exceptions occur with Coflex interspinous device. It increases range of motion by %19 and doesn?t effect disc loading force in flexion.ConclusionsBy the result of this study, we observed Coflex device can normalise disc loading forces but increases range of motion abnormally in flexion. Both devices don?t seem to be sufficient at motion preservation and load transmission in other directions of lumbar motion.Key WordsDegenerative lumbar spinal disease, nonfusion, posterior dynamic stabilisation, Coflex, Dynesys, finite element model.