Background: A large proportion of metal-on-metal hip arthroplasty failures are due to unexplained pain. The mechanism of failure has been thought to be associated with factors that increase material loss, including specific design features and surgical positioning of components. However, recent evidence suggests that there is not a simple dose-response relationship. An analysis of failed metal-on-metal hip arthroplasties involving a single design was performed in an attempt to help resolve this issue. Our aim was to identify the clinical and component variables associated with failure of metal-on-metal hip arthroplasties, particularly in patients undergoing revision arthroplasty because of unexplained hip pain, and to clarify the role of material loss.
Methods: We prospectively recruited fifty-five patients who were undergoing revision of a metal-on-metal Birmingham Hip Resurfacing System (BHR) arthroplasty (Smith & Nephew). We collected clinical data preoperatively, intraoperatively, and following the revision arthroplasty. Data included chromium and cobalt levels in whole blood, which were measured with use of inductively coupled plasma mass spectrometry (ICPMS), and component orientation, which was typically measured with use of computed tomography (CT) scans. The wear of the retrieved components was also quantified postoperatively. All parameters were compared with those in a comparable group of patients with a well-functioning BHR arthroplasty.
Results: Sixty-nine percent of the patients who underwent revision arthroplasty did so following a diagnosis of unexplained hip pain. When compared with patients with a well-functioning arthroplasty, patients who underwent revision arthroplasty had a significantly higher acetabular cup inclination angle (p < 0.01), a significantly smaller femoral head diameter (p < 0.01), and significantly higher blood cobalt and chromium ion levels (p < 0.01). However, almost 50% of the patients who underwent revision arthroplasty had blood metal ion levels below the clinical threshold of 7 ppb and low component wear rates of <5 μm/year.
Conclusions: In a large number of patients with unexplained hip pain leading to revision of a metal-on-metal hip arthroplasty, the acetabular cup orientation was satisfactory and the material loss rate was low. We suspect that patient-specific factors may have been responsible for the failure in a large proportion of these patients.
Investigation performed at Imperial College London, London, and the Royal National Orthopaedic Hospital, Middlesex, United Kingdom
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.
- Copyright © 2012 by The Journal of Bone and Joint Surgery, Incorporated
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