In Cervical Arthroplasty Only Prostheses With Flexible Biomechanical Properties Should Be Used for Achieving a Near-physiological Motion Pattern

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background:</jats:bold>In cervical arthroplasty, qualitative motion analysis generally investigates the position of the Center of Rotation (COR) before and after surgery.But is the prae-op COR suitable as reference? We believe that only a comparison against healthy individuals can answer whether a physiological motion pattern has been achieved. The aim of our study was to examine how the COR for flexion / extension after insertion of 3 biomechanically completely different types of disc prosthesescompares to healthy volunteers,and whether and how prosthesis design contributes to a more natural or maybe even worse motion pattern.<jats:bold>Methods</jats:bold>: In 15 healthy volunteers MRI in flexion and in extension was taken, and the coordinates for the CORs (COR-HV) from C3 to C7 were determined.Thenprae- and post-op flexion-/extension x-rays from 30 patients with a one-level disc prosthesis underwent analysis for determination of COR from C3 to C7; 10 patients who received a Bryan-, a Prestige STLP- or a Discover prosthesis were chosen, respectively. Change of post-op COR position wasinvestigated in relation to the COR-HV.<jats:bold>Results:</jats:bold>The pre-operative COR is not congruent with the COR found in healthy subjects and therefore cannot be used as reference for investigation whether a disc prosthesis resembles natural motion. However, the comparison with healthy individuals shows that Prosthesis-insertion can change the coordinates of the COR to any direction in all levels from C3/4 to C6/7 regardless of the operated segment. Prostheses with flexible biomechanical properties can contribute to shift the COR towards normal, but devices with unphysiological biomechanical design, like fixed ball-socket designs, for instance, can make the motion pattern even worse.<jats:bold>Conclusions</jats:bold>: In cervical arthroplasty, the biomechanical concept of the prosthesis has a significant impact whether a near-physiological motion pattern can be achieved or not.As it is rumor but not scientifically proofed that prosthesis-design has no influence on clinical outcome, surgeons should only choose devices with flexible biomechanical properties for disc replacement.</jats:p>