Measurement of material loss

The 2011 edition of the England and Wales National Joint Registry shows an increased failure rate for resurfacing and Large Head Metal-on-Metal (LHMoM) hips compared to other designs. The recent recall of the DePuy ASR has only increased the worldwide interest in the assessment of wear of explanted hip joints. The failure of these components has been linked to increased wear rates.
Worldwide there have been a number of reports of adverse soft- tissue reactions in patients who have undergone metal-on-metal hip replacement. The NJR in the UK has shown that LHMoM bearings have been seen to exhibit a higher revision rate when compared to conventional bearing surfaces. Furthermore these bearings have been seen to exhibit a markedly higher failure rate than the equivalent resurfacing replacements of the same design. This leads to the conclusion that some factor relating to the modular nature of the LHMoM bearings must be contributing towards this increase in revision rate.
Measuring the wear of explanted components allows a direct insight into the in-vivo behaviour of the implants. Wear analysis is a vital tool in determining failure mechanisms and ultimately improving the longevity of joint replacements through improved design and manufacturing control. To achieve this methods have been developed to quantify in vivo total joint replacement wear from retrieved total hip replacement components.
This study aims to improve the understanding of the interaction at the modular taper junction by developing a protocol for the measurement of material loss and resultant surface topography at this interface in clinically retrieved components.
A pilot study exploring the issues surrounding measurement of stem taper surfaces is presented.