[Friction in Hip Implants and Its Possible Consequences: In-Vivo versus In-Vitro]

Hip arthroplasty demonstrates excellent long-term outcomes with low revision rates. However, an increasingly younger and physically active patient population with high functional demands on the artificial joint has led to increased material-specific requirements. Friction between the articulating components of an artificial hip joint is a relevant factor that may ultimately determine implant longevity. The aim is to keep friction as low as possible in order to avoid excessive loading at the implant-bone interface, as this can lead to loosening of the artificial hip joint. Friction in the hip joint is multifactorial and can be influenced by patient-specific, implant-specific and surgery-related factors. Therefore, it is highly relevant for arthroplasty research to investigate friction under varying implantation angles, patient activities, and material combinations. In-vivo studies can be used to investigate friction directly in the patient under physiological conditions. Individual influencing factors, on the other hand, can be optimally investigated in in-vitro simulations, as possible confounding variables can be controlled and kept constant. The various approaches to measuring friction and the results from the literature to date are summarized below. In addition, the advantages and disadvantages of the various measurement methods are discussed, and an outlook is given on the possibility of combining in-vivo and in-vitro friction tests to further optimize patient care in total hip arthroplasty.