Understanding Movement and its Influence on Tribology of the Human Hip

Total hip arthroplasty is one of the most successful and innovative medical procedures developed during the 20th century. Success post-op has been shown to decrease for younger, more active patients when compared to those who are older and less active, raising concerns surrounding the reasons behind the increased risk of prosthesis failure for some individuals. Sliding distance, cross-shear, load and edge loading are important factors when determining potential wear rates at the hip.
Global and local hip biomechanics were calculated for eighteen healthy subjects, completing thirteen common daily activities. Results showed variation in cross-shear motion and hip reaction forces between individuals and across activities. Variation in motion paths and loading, between and within activities, suggested variation in the fluid film thickness and corresponding lubrication regimes at the joint. Walking tasks showed high levels of cross-shear and the potential for excessive wear both at initial contact and heel-off. More linear activities, such as sitting and standing, showed low cross-shear alongside a potential risk of posterior edge loading. Tribological discrepancies were shown between hip simulator input data (ISO) and measured walking data, with the ISO cycle potentially underestimating cross-shear wear at initial contact, during walking.
Results provide detailed data that may facilitate improvements in the reliability of pre-clinical testing for hip prostheses and tissue engineered cartilage substitution. The data indicates that durability testing standards should consider incorporating a range of activities, rather than just walking, and aim to represent the variability shown between individuals. Results also provide evidence for determining the appropriateness of specific activities/ rehabilitation for post-operative total hip replacement patients.