Abstract
Introduction
Adverse wear related failure (AWRF) after metal-on-metal hip resurfacing arthroplasty (HRA) has been described as a new failure mechanism. We describe the results of revision of these failures.
Methods
Between July 1999 and Jan 2014, a single surgeon performed 3407 HRA. Nine (9/3407; 0.3%) cases in 8 patients were revised due to AWRF. In two additional revisions for AWRF the primary HRA was done elsewhere. There were a total of 11 revisions (9 women, 2 men) for AWRF cases reported in this study. The primary diagnoses were OA in 7 and dysplasia in 4. At the time of the primary surgery, the average age was 50±5 years and the average BMI was 27±4. The average femoral component sizes were 46±3mm. Only the acetabular component was revised in eight cases, both components were revised in 4 cases (revised to THA), three of these four used metal on metal bearings. A postop CT was requested for all patients after revision. 4 scans were of sufficient quality to analyze implant positions. Algorithms for metal artifact reduction were utilized to obtain high quality 2D images (Figure 1); 3D CAD models of the bones and implants were regenerated in order to calculate the acetabular inclination and anteversion angle (Figure 2).
Results
Prior to revision, all 11 cases had acetabular inclination angles on standing radiographs (AIA) greater than 50° (mean 560 range: 51°-60°) and Cobalt blood levels greater than 10ug/L (mean 94±64ug/L, range: 12–173 ug/L). Chromium levels were a mean of 50±33ug/L (range: 8–111 ug/L). 3D studies showed fluid collections and metalosis was seen in all cases. The mean follow-up length after revision was 2.4±1 years. In 4 cases the postop CT could be used to accurately measure implant positions resulting in a mean AIA=34°±9° and a mean anteversion angle of 18°±4°. Metal ion tests were available for 7 cases at least 1 year after revision. Cobalt levels were reduced to a mean of 4.1±3.1 ug/L (range: 1.5–6.2 ug/L) and Chromium levels fell to 6.3±2.9 ug/L (range: 3.4–10.9 ug/L). The mean HHS was 93±15. There was one failure of acetabular component fixation, which required repeat revision. Her latest HHS was 100 one year after the second surgery. For all revisions, the mean operative time was 123±15 min, incision length was 5±1 inches, estimated blood loss was 258±82 cc, and hospital stay was 1.3±0.5 days. There were no other major complications including no nerve palsies, vascular injuries or abductor mechanism disruptions. No patients limped.
Conclusion
Our study suggests AWRF in HRA can successfully be revised with metal-on-metal surfaces. Revision of the femoral component is not necessary despite the abnormal wear. Correction of the steep AIA is the key to success. This confirms the concept that edge loading, leading to a high wear state, rather than allergy to metal is the cause of these failures.
