Adverse reaction to metal debris: metallosis of the resurfaced hip

The greatest concern after metal-on-metal hip resurfacing may be the development of metallosis. Metallosis is an adverse tissue reaction to the metal debris generated by the prosthesis and can be seen with implants and joint prostheses. The reasons patients develop metallosis are multifactorial, involving patient, surgical, and implant factors. Contributing factors may include component malposition, edge loading, impingement, third-body particles, and sensitivity to cobalt. The symptoms of metallosis include a feeling of instability, an increase in audible sounds from the hip, and pain that was not present immediately after surgery. The diagnosis is confirmed by aspiration of dark or cloudy fluid from the effusion surrounding the hip joint or by laboratory testing indicating a highly elevated serum cobalt level. Metallosis can develop in a hip with ideal surgical technique and component placement; conversely, some patients with implants placed with less than ideal surgical technique will not develop this complication. Among patients with bilateral hip implants, if metallosis develops it may involve only one hip. Bone loss and tissue necrosis can develop if metallosis is untreated and continues to progress. Surgery is the only effective treatment for progressive metallosis. If there is adequate bone remaining, the acetabular component can be repositioned, keeping the metal-on-metal resurfacing prosthesis. In some patients, it also is possible to change the bearing surface to metal-on-polyethylene. Total hip replacement is an alternative for patients whose resurfacing procedure is complicated by metallosis. Advanced cases may present additional challenges; thus, early surgery is recommended.