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We thank Drs. Amstutz and Le Duff for their thoughtful letter regarding our study . Specifically, they take issue with our Discussion section and the statement regarding the performance of metal-on-metal (MOM) devices as a class. I suspect they would agree that when taken as a class and grouped together as MOM devices they do not perform as favorably as the metal-on-polymer devices in the registry data. Their point is well taken that it likely is not fair to group all of the MOM devices in this fashion as the different devices have varied results reported in the literature. Some devices have fared better and functioned well in many patients. However, we believe the articular surface replacement (ASR™) device is not the only one with failure issues and therefore this class of devices needs further scrutiny and followup. The unanticipated mechanisms of failure in metal devices related to unintended edge loading and corrosion are real and the class of devices needs to be monitored.
We also recognize that resurfacing is different than large-head total hip replacement and success rates vary from center to center and among patients. Drs. Amstutz and Le Duff reference some formidable results in their letter yet we continue to be confronted with registry results that question MOM devices as a class. Smith et al. recently reported on the National Joint Registry for England and Wales and found that hip resurfacing as a class did not perform as well as contemporary THAs [2, 3]. This particularly was the case for female patients and only male patients with large heads had results that were similar to THA results. Their studies grouped MOM resurfacing and did not separate device performance and we suspect Drs. Amstutz and Le Duff would take issue with that.
(Re: Hug KT, Watters TS, Vail TP, Bolognesi MP. The withdrawn ASR™ THA and hip resurfacing systems: how have our patients fared over 1 to 6 years? Clin Orthop Relat Res. 2012 Aug 28. [Epub ahead of print]).