THE DETERMINATION OF THE VOLUMETRIC WEAR FOR SURGICALLY RETRIEVED HIP IMPLANTS BASED ON CMM

The effects of wear mechanisms on the long-term survivorship of artificial hip implants emphasized the importance of determining the 3D volumetric wear in retrieved hip replacements. Traditional methods for determining the volumetric wear on acetabular cups require reference surface from a pre-worn model, which is not feasible for clinical retrieved implants. In this study, a methodology based on co-ordinate measuring machine (CMM) measurement is proposed to reconstruct the reference surface by applying a mathematical model on those selected unworn regions of the acetabular liners. For validation purposes, three polyethylene liners from 5-million-cycle hip simulator testing were employed, whose wear volume at different measurement points was determined by applying the developed method and the results were compared to those determined via traditional approaches. Volumetric loss estimated by the developed method was found to correlate well with the results estimated by the traditional methods ((Formula presented.)). Moreover, two surgically retrieved inserts were analyzed using the developed methodology. The wear volume estimated from the two retrieved liners was also found to agree well with the observation from X-ray photograph. Results demonstrated that the proposed method is effective in determining the volumetric wear for retrieved components providing viable unworn regions on the liner.