Introduction: Physiological cervical intervertebral motion inherently induces a neuroforaminal volume change. Integration of an artificial motion component within this intervertebral kinematic system may cause neuroforamina to lose their ability for continuous and instantaneous volume adaptation, inducing foraminal stenosis. The purpose of the current study is to virtually simulate a newly developed cervical total disc replacement (TDR) to evaluate the neuroforaminal dimensions at rest and during motion.
Materials and methods: In a three-dimensional computer-aided design model of the spine, the Cerkinetic (OrthoKinematica Ltd., Haifa, Israel) TDR was virtually implanted at the C5-C6 disc space. The TDR consists of a bearing mechanism with an elliptical protuberance and a recess, allowing a progressive increase of the intervertebral axial spacing in all three dimensions and in line with flexion and extension. Translations are performed in accordance with the physiological forces influencing the disc space and spinal continuum. The minimal proximal neuroforaminal width was defined and evaluated at rest and motion.
Results: A progressive increase (15.2% at 6 degrees) in flexion and a decrease (12.3% at 6 degrees) in extension of the neuroforaminal width were observed. With axial motion, a progressive increase (44.6% at 6 degrees) of the right neuroforamen width as well as a decrease of the left neuroforamen width (15.3% at 6 degrees) were seen.
Conclusion: The TDR under investigation simulates the intervertebral kinematics, allowing a physiological adjustment of the facet joints in rest and motion. This preserves the ability of the neuroforamina to maintain their capability of changing their dimensions.
Georg Thieme Verlag KG Stuttgart · New York.