[TKA kinematics. In vivo techniques and results]

Until now it remains less clear to what extent the different types of endoprostheses can simulate the physiological motion pattern of the knee joint. The aim of this study was to present fluoroscopy and functional MRI as well as the results of these in vivo imaging techniques for TKA kinematics. Videofluoroscopy is a dynamic investigation, analyzing the subjects under fluoroscopic surveillance during different activities. Three-dimensional (3D) kinematics were recovered from the two-dimensional fluoroscopic images using a model-fitting technique. Kinematic analysis with functional MRI was performed in an open MR system at different flexion angles with external loads being applied during imaging. Femoropatellar and femorotibial 3D kinematics were analyzed by image postprocessing. The findings in healthy knees obtained with functional MRI under static conditions are in good agreement with the fluoroscopic outcome under dynamic conditions. In all investigated TKA in the mean an increased external rotated position of the femur relative to the tibia was observed at full extension, while the amount of external rotation during knee flexion was decreased. Although there was great variability among the individuals, differences were observed between the TKA-groups (e.g. posterior stabilized vs PCL retaining). Significant changes of femorotibial and femoropatellar kinematics were found in TKA compared to healthy knees, which may lead to early aseptic loosening or increased polyethylene wear The presented techniques and results allow for advanced in vivo diagnostics and may help to improve the design of TKA and to enhance the long-term performance.