Einfluss zweier Bandscheibenprothesen auf die Kinematik des C3/C4-Segmentes

Abstract

Degeneration and traumatic damage of the intervertebral disc are a prevalently occurring and also socially relevant problem. Although criticized to induce adjacent segment disease (ASD) as a possible long-term complication, intervertebral fusion still is the gold standard of surgical treatment. Total disc arthroplasty (TDA) is supposed to avoid ASD due to prevent segmental motion and kinematic performance. In this study the kinematics of C3/C4-segments was analysed before and after total disc arthroplasty with Prestige LP® and Bryan® Cervical Disc. Eight human segments were tested applying triangularly varying, axial, sagittal or frontal torque. Additionally axial, flexional/extensional or lateral-flexional directed preload was applied. Segmental motion was detected by a high resolution 6D-measuring apparatus. Detected kinematic parameters were the position, direction and migration of the instantaneous helical axis (IHA) during segmental motion, as well as segmental stiffness and range of motion (ROM) before and after TDA. In all cases IHA-direction was mostly independent of the amount of axial preload, rotational angle and TDA. IHA was rotated backwards in all cases of axial rotation and lateral flexion and was not directed parallel to the applied torque. In contrast it was parallel to the torque for flexion/extension. Despite of changing the shape of IHA-migration, we found commonly trends after TDA and a significant dorsal shift of IHA-position (dorsal shift: Prestige LP®: 5,9 mm, Bryan®: 8,15 mm) in axial rotation after TDA. In lateral flexion a cranial shift could be found (Prestige LP®: 5 mm, Bryan®: 8mm). In both cases the amount of the shifting was influenced by the position of pre-load. The Bryan-TDA increased the initial rate of IHA-migration for axial rotation. Furthermore we observed a significantly loss of segmental stiffness, which involved a larger range of motion. In conclusion total disc arthroplasty with Prestige LP® and Bryan® Cervical Disc alters the kinematic properties of C3/C4-segments. Due to the shift of IHA-position after TDA, additional translation of the vertebra can be found, which affects the kinematics of the adjacent levels and possibly generates adjacent segment disease.