Abstract
Background
Post-market surveillance is necessary to ensure the safety and efficacy of newly introduced technologies and implants. The Birmingham Hip Resurfacing (Smith and Nephew, Inc., Memphis, TN) was the first hip resurfacing implant approved for use by the US FDA in May 2006. A prospective, multi-center postmarket approval study has been in progress to assess safety and efficacy of this implant.
Methods
Patients meeting inclusion criteria were enrolled at five sites. Clinical evaluation and radiographs were obtained at 3 months and 1 year, and annually thereafter for a total of 10 years. Blood metal ion levels were measured at 1 year and 4 years.
Results
265 patients have been enrolled thus far with 193 males; 28 patients have had bilateral procedures. The average age of the patients is 51.3 years (range 22–72). There have been 7 revisions (2.4%) in the entire cohort to date: 2 were for femoral neck fracture, 2 were for acetabular loosening; 1 was for femoral head osteonecrosis; 1 was revised on the day of surgery for errant implant placement; and 1 was for pseudotumor. K-M survival curves for the cohort are 97.8% at 5 years (Figure 1); men had 99% survival, while women had 94.5%. Whole blood metal ion analysis revealed a median cobalt and chromium levels of 1.5 ppb and 1.7 ppb at 1 year. There was a significant difference between the metal levels in men and women, however women also had smaller component sizes. Furthermore, a significantly higher percentage of female patients had outlier metal ion levels > 7 ppb.
Conclusions
This hip resurfacing device has demonstrated safety and efficacy comparable to THR, in this multicenter postmarket approval study. A gender difference in the survival rate and median metal ion levels does exist; therefore, it is important to continue close monitoring of this cohort to determine longer term results.
