"The friction acting in vivo in the artificial hip joint - what are the tribologically relevant influencing parameters in vivo?"

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Implantation of an artificial hip joint considered today as the most successful orthopaedic operation of the century. Although it is extraordinarily successful for patients between 65 - 79 years with an average 10-year revision rate of only 5%, the revision rate for younger and more active patients is three times higher with 15%. Optimization of implant surfaces, bearing couples and surgical techniques have not led to any significant improvement in longevity over the last two decades. In addition to the friction acting in vivo and the resultant implant wear, incorrect positioning of the implant components in particular are discussed as potential reasons for failure. The joint friction occurring in vivo is a multifactorial factor for the survival of the artificial joint replacement. Accurate intraoperative positioning of the components within a "safe zone" is an essential factor for the short- but also long-term survival. Our own work has shown that the intraoperatively adjusted joint roofing is a primary key parameter for joint friction occurring postoperatively in vivo. However, a systematic and fully comprehensive investigation of all potentially influencing parameters, which are needed for the adaptation and design of tribologically optimized "safe zones", does not exist yet. In order to be able to realize such a biomechanical-tribological optimization more detailed investigations of the friction in vivo are necessary. Among others, the project will investigate the relationship between the in vivo stress from contact forces and friction on the cup and the resulting stresses in the interface to the pelvis. In addition, the influence of various activities on the sliding and lubricating conditions, as well the influence of the pelvic tilt on the joint and friction loads and its change in the postoperative course will be systematically investigated. Based on the close cooperation of the Julius Wolff Institute (Berlin Institute of Health at Charité) and the Laboratory of Biomechanics and Implant Research (Heidelberg University Hospital), this project will create for the first time the possibility to analyze specific parameter of friction systematically in a unique combination of in vitro and in silico approaches and in vivo measurements.