Quantifying the wear of acetabular cups using coordinate metrology

In an ageing population where individuals demand a pain free and active existence, hip arthroplasty has become one of the most important operations of later life, with developments increasing the longevity of this prosthesis. Accurate assessment of wear is an important way to assess how well hip prostheses perform over time. This paper describes a new protocol to accurately locate and map the wear of acetabular cups. 16 metal-on-metal acetabular cups were tested in a hip simulator for up to 6 million cycles at a range of angles of inclination in order to create a large range of wear volumes. Unworn and worn regions of acetabular cups were digitised in two separate scans using a CMM. The two scans were superimposed in order to allow calculation of maximum depth, wear volume loss and rim damage. Values obtained from the CMM protocol (CMM) were compared to the wear volume determined gravimetrically (G); a strong correlation (CMM = 0.992G−0.504) was established. The CMM protocol established was shown to be a methodology more powerful than many existing geometric protocols which could be used to assess explants and implants tested in vitro.