Hip resurfacing devices have only become available in the U.S. in the last two years (Smith & Nephew introduced the BHR in 2006 and Stryker began distributing Corin's Cormet in 2007), and with the relatively recent launch comes an "incomplete" clinical understanding of the patients and techniques best suited for the technology. This month's JBJS features an article summarizing the lessons learned about hip resurfacing from the Cormet's IDE.
The Cormet study was initiated in 2001 at 12 centers. 337 patients (228 male and 109 female) participated. A 1998 study of ceramic-on-ceramic total hip arthroplasties in 266 patients was used as control data, with the authors of this article commenting that one of the weaknesses of the data is that the control study was not done by the same investigators. However, the cohorts were similar, except for age, which was slightly older in the THA study. A measure, new at the time of the study, called the composite clinical success score was used to assess non-inferiority for the Cormet device.
Results confirmed non-inferiority for the Cormet, and at minimum follow-up of two years, Harris hip scores were comparable between the two groups. Rates of adverse events were also similar between the groups (9.5% in the investigational group compared to 7.9% in the control group.) Despite the overall similarities in results, the authors identified a number of opportunities to improve patient outcomes for resurfacing systems.
The overall revision rate in the IDE group was significantly higher than the control group. 24 of the patients in the IDE group (7.1%) required revision, compared with only five patients (1.9%) in the control group. The article offers several reasons why the revision rate would be so much higher for resurfacing, pointing out that "rigorous patient-selection criteria and extensive technical training were not features of this investigation," while the ceramic-on-ceramic control devices were implanted by surgeons very experienced in THA procedures.
These stand out in the article as the main opportunities to improve resurfacing outcomes, with the authors also identifying three specific risk factors:
- Female gender. 13 (12%) of the 109 female patients in the investigational group had a revision compared with 11 (4.8%) of the 228 male patients.
- Component size. The device failed in 13 (17%) of the 87 patients with a 40 or 44-mm femoral component. It failed in 11 (4.2%) of 259 patients with a 48, 52 or 56-mm component.
- Pre-op Harris scores. A decrease of five points in the preoperative Harris hip score (a measure used to assess pain and function) increased fracture risk by a factor of 1.32.
Overall, the study calls resurfacing an "appropriate alternative" to THA, for certain patients and with attention to certain technical aspects of procedure (such as component size.) For these properly-selected patients, who are younger and more active than a traditional THA patient, hip resurfacing represents an opportunity to treat pain and reduced function earlier in the continuum of care, preserving tissue and leaving future surgical options open.
