gms | German Medical Science

Objective: There is a need for accommodation of the foraminae during physiological movement of the cervical spinal motion segment. If their volume is decreased too much, there will be irritation of the nerve root. By implanting artificial disc replacements the segmental motion could be preserved. Questionable is still the quality of motion pattern in comparison to intervertebral space’s proper natural kinematic, especially compensatory displacement. If motion is denaturated foraminae may lose their continuous instantaneous volume adaption. Logically consistent this will lead to impingement of the nerve root in various degrees. The goal will be to providing a cervical disc prosthesis which would emulate the natural intervertebral motion, maintain foraminal volume and avoid transforaminal undesired shearing forces.

Methods: Elevation in flexion, extension and lateral bending axes versus angular displacement was evaluated in a 3D CAD simulated model of a special formed cervical TDR (Cerkinetik™). The prosthesis was virtually implanted within C5-6 solid cervical 3D simulated cervical spine. Elevations were recorded. Volume, dimensions and shapes of the foraminae were evaluated and graphically analyzed.

Results: Mean prosthesis simulated elevation in all 3 axes is ~0.5 mm. See graphic foraminae analysis.

Conclusions: Natural foraminae volume was preserved assumable due to TDR geometry and the consequent induced characteristic motional pattern. Unnatural shearing forces that might distort the foraminae and impinge nerve roots are avoided. The motional versatility conferred by specific geometry of the examined prosthesis as described and demonstrated, enables the facet joints to assume their natural position adjustment as an integral component of the treated level milieu.