Hip resurfacing implant offers lower revision, complication rates for hip arthritis

Joseph Daniel, FRCS, MS(Orth); and Derek McMinn, MD, FRCS

When the Birmingham Hip Replacement was approved by the FDA, the manufacturer was required to conduct a post-market approval study. This included a longer-term safety-effectiveness study on the first 350 consecutive cases of the inventor surgeon through annual questionnaires and 10-year clinico-radiographic examination (U.K. study), and a prospective multicenter study in the United States to evaluate the learning curve and safety-effectiveness in 350 patients including questionnaires, periodic clinico-radiological and metal ion assessments.

The U.S. study is ongoing and the U.K. study is completed. Reports from both studies confirm device safety and efficacy. The learning curve in the multicentre trial is reflected in the instances of femoral neck notching and incomplete cup seating, which however did not increase the revision rate significantly. The cumulative implant survivorship of 97.6% at 5 years in this young cohort (mean 51 years) is within the new U.K. NICE benchmark and compares well with the results from Birmingham. One reason for the trend toward a higher failure rate in women in both reports is the higher prevalence of developmental dysplasia.

The low incidence of radiological adverse features shows that the implant system is biomechanically compatible in the long term. The low and incrementally non-progressive median metal ion levels and the low incidence of adverse local tissue reactions show that it is biologically compatible. The multicenter U.S. study demonstrates that the Birmingham Hip Replacement is a safe and effective option in young patients, especially in men, and that the results are generalizable and transferable.

Reference:

Daniel J. Results of Birmingham hip resurfacing at 12 to 15 years. A single-surgeon series. Bone Joint J. 2014. In Press. 

Thomas P. Vail, MD

This article is an important addition to the literature describing the results of metal-on-metal hip resurfacing in the United States using the Birmingham device. The strengths of the study are that it is a multicenter prospective study and there were few exclusions. The surgery was performed by experienced surgeons, which is important in assessing the generalizability of the results. 

When interest in hip resurfacing began to accelerate prior to 2010, there was concern about the risk of failure due to technical factors, and less awareness of the potential impact of the bearing material.  This study demonstrates that when performed by experienced surgeons, the risk of acetabular loosening, femoral component loosening and femoral neck fracture is low. Consequently, the revision rate at 2 years is also low (2.4% overall).  

This study does not put to rest concerns about the biologic impact of metal ions, or whether this bearing material is suitable for women and small stature men given the discrepancy in survival for women vs. men.  While the median whole blood levels of cobalt and chromium for the entire study cohort were below 2 ppb, a high degree of variability was noted, with women having a 7.3% incidence of outlier values vs. only 1% of male patients.  Importantly, the authors reported only one revision for adverse tissue reaction to metal in a male patient at 3 years after surgery.  However, it is not known whether this finding will increase as the length of follow-up increases from the mean 3.6 years reported in this study.

In conclusion, this study represents exactly the type of careful post-market surveillance that should be widely adopted in our field when new technology is introduced, demonstrating the evolution in the reasons for revision over time.