Influence of implant positioning and configuration on kinematics and pressure distribution in the knee joint

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In the implantation of total knee endoprostheses, joint surfaces destroyed by arthrotic wear are resected and replaced by artificial surfaces. Despite the very good pain relief and high durability of modern knee prostheses, about 20% of patients remain dissatisfied with the result. There are currently two different approaches to the alignment of prosthesis components in professional circles: Mechanical Alignment (MA) and Kinematic Alignment (KA). The goal of KA is to restore the natural orientation of the tibio-femoral joint line, the natural leg axis and the natural stability of the knee joint. In order to estimate the possible long-term success of prostheses implanted according to KA principles, it is essential to know the mechanical loads acting on the prostheses and to compare them with an MA implantation.The aim of the project is to compare the effect of the alignment of the prosthesis according to KA and MA as well as additionally different prosthesis designs on biomechanics. Thus, a possible improved function in patients should be attributed to mechanical parameters and a conclusion about the possible long-term success with regard to mechanical loading should be made.Within the scope of the project, the following working hypotheses are to be tested:(1) Kinematically oriented prostheses show biomechanical parameters more comparable to the physiological native state compared to mechanically oriented prostheses (medial and lateral contact forces, retropatellar pressure, patella kinematics, femoral rollback).(2) Double cruciate ligament retaining prosthesis designs provide more comparable biomechanical values to the physiological state than prosthesis designs with only one or no cruciate ligament at all (parameters see 1.).The project is divided into an experimental and a simulative part, which are closely interlinked. In both parts the working hypotheses will be tested. The experimental investigations will be performed in a comprehensive in-vitro test setup. The muscle traits of the most important knee extensors and flexors will be controlled by a hydraulic system and the knee will be guided and loaded by an industrial robot. With the help of the data obtained from the in-vitro tests, an existing numerical knee model is to be extended. Among other things, the strains of ligament structures, which cannot be directly measured, will be determined. In addition, a variation of implantation parameters will be carried out to estimate their influence on biomechanics.In a further approach the knee model will be integrated into a complete model of the lower extremity. This will allow existing data from an ongoing clinical study with n=120 (n=60 KA and n=60 MA) patients to be analyzed in detail. Using these data in conjunction with the extended model, it can be shown how biomechanics are influenced by different prosthesis alignment not only on the idealized test bench but also in the real patient.