Dynamik der Hüftschaftimplantation

In cementless hip arthroplasty, mallet blows are used to advance the rasp during the preparation of the femoral canal, to implant the prosthesis, and to join the implant components. The strength of the mallet blows is crucial for a stable press fit, while the dynamics of the involved instruments and the interaction with the femur-tissue system are complex and individual. Therefore, the aim of this study is to investigate the influence of patient- and surgical approach-specific characteristics on the dynamic behavior of the femur-tissue system as well as the force transmission of surgical instruments. The experimentally determined parameters of the femur-tissue system of the human bodies examined varied depending on the positioning on the operating table, which in turn depended on the surgical approach. However, for both surgical approaches examined, the values resulted in a relatively low natural frequency (lateral: 6.7 Hz, direct anterior: 9.6 Hz). Consequently, metal-on-metal mallet blows or comparable short impulses from automated surgical impaction tools lead to overcritical excitation. As a result, the implant is inserted into the femur before the bone itself even starts moving. The experimental and numerical analyses revealed a significant attenuation of the mallet force by the impactor. The design of the impactor had a significant influence on the force transmission: lighter impactors transmitted higher peak forces than heavier variants. Even minor design modifications resulted in differences in the transmitted force by a factor of two. Due to the overcritical excitation, it is not necessary to make intraoperative adjustments of the surgical technique to the patient's positioning or to the mass and stiffness of the surrounding soft tissue. However, the utilization of different impactors can lead to considerable deviations in force transmission. Without adequate briefing for orthopedic surgeons, changing the implant system, the associated instruments, or the surgical approach can increase the risk of complications such as periprosthetic fractures or aseptic loosening.