Analysis of failed metal-on-metal hip prostheses J. Lord, T. Joyce School of Mechanical and Systems Engineering Newcastle University Abstract Replacement joints, or prostheses, are an important tool for reducing pain and restoring functionality to patients with diseases such as arthritis. However, even the most modern prostheses have a limited life span and a major cause of failure is wear. A Matlab program was written to aid analysis of retrieved hip prostheses. Utilising data collected from a Mitutoyo LEGEX322 co- ordinate measuring machine (scanning accuracy within 0.9μm), this program is capable of several analytical techniques; most notably calculating the volumetric wear of a sample. In addition to numerical outputs, the program also returns graphical outputs which allow the user to visualise the wear patterns, and provide means for further analysis. It has been used to examine both femoral heads and acetabular cups from metal-on-metal hip prostheses for wear patterns and severity. This method has allowed identification of samples which exhibit several times more wear than has been suggested previously. Wear depths of up to 150μm and volumes up to 94mm 3 have been demonstrated. Preliminary analysis suggests that wear volumes are directly related to the acetabular cup position in the body. With greater understanding of the causes of wear (and therefore failure), prosthesis longevity can be increased for the long term benefit of patients. 1. Introduction Attempts at replacing the diseased hip joint can be traced back as far as 1890 when Gluck described the use of ivory to replace the femoral head [1]. Early attempts were largely unsuccessful and more recent developments in hip prostheses owe much to the work of Charnley in the 1960s and 1970s [2]. These designs consisted originally of a stainless steel femoral stem and head, an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup and bone cement or screws for fixation. Although this prosthesis has shown good long-term survivorship in some cases [3], there have also been numerous studies reporting early failure [4, 5]. Wear of the UHMWPE component has been cited as a particular reason for failure and has been linked with osteolysis [6], an autoimmune reaction leading to bone resorption, implant loosening and ultimately implant failure as well as potential medical problems.