How Patients' Lifestyle Affects the Wear of Hip Implants: An In-Silico Study

The validation of new hip replacement designs traditionally relies on lengthy and costly In-Vitro wear tests that replicate basic In-Vivo conditions, as the simplified walking recommended in the ISO 14242 guidelines. These tests overlook the diverse motor tasks and lifestyle differences among patients. This study seeks to establish the foundation for In-Silico clinical trials of total hip replacements, enabling wear simulations of patients with different lifestyles, not feasible with In-Vitro tests. The impact of diverse kinematic and loading histories on the wear of metal-on-plastic hip replacements is investigated in a novel way, considering the combined effect of six daily activities (e.g., walking, fast walking, sit/stand, stairs up/down, lunging), different activity frequencies across five patient profiles (from sedentary elderly to active young), and the effect of load sequence. The results reveal that both the type and frequency of motor tasks significantly influence implant wear. The most critical tasks and at-risk patients were stair climbing and the most active individuals, regardless of age. Load sequence also plays a key role in long-term wear predictions. Accuracy and computational cost were balanced by simulating walking, stair climbing, and sit/stand cycles, ensuring equivalent wear to a complete motor task sequence. ISO standards conditions notably tend to underestimate volumetric wear by up to 60% compared to the simulated patient types. They also fail to predict realistic wear patterns for activities like squatting and lunging where edge contact occurs.