ABSTRACT

The aim of this study was to analyze the effect of two popular interspinous devices (Coflex® and Coflex® Rivet), considering the range of motion and disc loading characteristics at surgical and adjacent segments, with the finite element method (FEM).

Three functional spinal units in the lumbar region (L3–4 and L4–5) were modeled by FEM. Then, the Coflex® and Coflex® Rivet interspinous devices were modeled and implanted virtually at the L4–5 segment of the lumbar vertebrae by FEM. Flexion, extension, bending, and rotation forces were applied to these two models and one intact vertebral model. The range of motion and disc loading forces at the L3–4 and L4–5 levels were measured and compared in these three models.

There were four main findings of this study: (1) The Coflex® Rivet device provided stability in all movement directions while allowing a range of motion, especially flexion; (2) Coflex® Rivet decreased 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.

In conclusion, the Coflex® Rivet device decreases the disc loading and range of motion at both the 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 for the same functional spinal units.