Biomechanical comparison between Coflex and Coflex rivet; afinite element modeling study

IntroductionThe aim of this study was, to analyse the effect of two popular interspinous devices (Coflex® and Coflex Rivet? ) to the range of motion and disc loading characteristics at surgical and adjacent segments with finite element method (FEM).Materials and MethodsTwo functional spinal unit at lumbar region (L3-4 and L4-5) are modelled by FEM. Then Coflex® Interspinous Device (Paradigm Spine, LLC, New York, NY) and Coflex Rivet? (Paradigm Spine, Wurmlingen, Germany) were modelled and implanted virtually at L4-L5 segment of lumbar vertebrae by FEM. Flexion, extansion, bending and rotation forces were applied to this two models and one intact vertebrae model. Range of motion and disc loading forces at L3-4 and L4-L5 levels were measured and compared in this three model by FEM.ResultsThere were four main findings in current study: (1) The CoflexRivet? device provided stability when allowing range of motion specially in flexion, (2) Coflex Rivet? decreased the disc loading as well as range of motion in all plains at the surgical segment, (3) Coflex Rivet ? decreased the range of motion and annular stress in the upper adjacent segment, (4) both devices decreased the range of motion and annular stress in extension, bending and rotation in both the surgical and upper adjacent segments.ConclusionIn conclusion, Coflex Rivet? device decreases the disc loading and range of motion at both surgical and upper adjacent segments in comparison with the original Coflex® device in flexion. In extension, bending and rotation; both devices show similar biomechanical characteristics in the same functional spinal units.