Evaluating hip implant wear measurements by CMM technique

Wear of the bearing components is a major factor affecting the performance of hip implants. Wear analysis is thus one of the most important processes for understanding of how wear occurs and its location and development, with an aim to improve the success rate and longevity of total hip replacements. This study presents wear measurement and analysis of polyethylene acetabular components using a coordinate measuring machine (CMM). An uncertainty analysis was performed to validate CMM wear measurements. Measurements were made with an increasing number of scanning points on retrieved ex vivo implants to investigate the effect of the number of scanning points on wear measurements. CMM wear measurements were compared to in vivo radiographic measurements (RSA) and volumetric wear estimates made using well-established analytical formulae. The number of scanning points has insignificant effect on wear quantity and measurement uncertainty. CMM linear wear measurements closely match those made using RSA, whereas theoretical volumetric formulae applied to CMM and RSA measurements both appear to overestimate wear volume. The findings further emphasize potential benefit of using CMM ex vivo and RSA in vivo to assess polyethylene wear after total hip replacement surgery. Further, it is shown that identifying key components of the measurement uncertainty are important to improve the accuracy and the reliability of CMM wear measurement.