Wear and loosening in THA: results from a multidirectional simulator

Wear and loosening remain major concerns in total hip arthroplasty (THA), particularly in younger, more active patients who demand long-lasting implants. This study investigates wear behavior in three common prosthetic geometries and their material combinations using the TUNIS-3DOF hip simulator under physiological load conditions while adhering to ISO guidelines. A total of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups were combined with stainless steel (SS316L), cobalt-chromium-molybdenum (CoCrMo), and zirconia (ZrO₂) femoral heads and subjected to six million gait cycles. All configurations exhibited a biphasic pattern of wear: a high wear "running in" phase, then a level linear regime. Zirconia heads had the lowest wear rates, while SS316L had the highest wear rates, especially exhibited in the early phases of testing. Both increased head diameter and decreased cup thickness both increased wear substantially, such changes commercially could be problematic regarding osteolysis and loosening. The change from abrasive to adhesive was related to radial stress, helped by analytical modelling. These results support the possibility of using reinforced or thicker cups, which may be made by incremental forming or additive methods, to strengthen implant longevity. This research assists in the process of maximizing THA designs to provide prolonged longevity and clinical results-especially in mechanically demanding patient populations.