MOM Failure Modes: An In-Depth Look at Metal Ions and Implant Wear

Contemporary MOM bearings (large-diameter heads) offered the perceived benefits of much greater range of motion and greater stability with reduced risk of impingement and dislocation. A variety of design and Both positive [1-3] and negative reports [4-8] have now emerged with regard to total hip arthroplasty (THA) and resurfacing arthroplasty. As a result, there has been an avalanche of studies focused on critical issues such as: surgical positioning, shallow cups (face angles 144-170°) [9-11] and “edge loading”. [5,7,12-17] However, there are several, possibly synergistic, risk scenarios that could trigger adverse MOM wear and very little progress has been made in understanding such interacting parameters. In an effort to understand the role of metal ion analysis and how it relates to revision surgery and implant wear, selected MOM revised cases were reviewed [28]. Retrieval data was included in conjunction with metal ion analyses and intraoperative observations to determine various failure modes. We suggest MOM devices that are well fixed but fail after 2 years can be classified into one of six modes: (i) normal, (ii) allergic reaction, (iii) 3rd body wear, (iv) repetitive subluxation with metal impingement, (v) multi-directional subluxation with soft tissue impingement, and (vi) repetitive subluxation with soft tissue impingement.