Aim: The purpose of this study was to analyze the in-vivo wear rates of Birmingham Hip Resurfacing (BHR, Midland Medical Technologies Ltd., Birmingham, U.K.) explants and to contrast the results to the wear rates of conventional 28 mm metal-on-metal bearings (Metasul, Zimmer GmbH, Winterthur, Switzerland).

Methods: The wear rates, measured by a coordinate measuring machine (CMM5, SIP, Geneva, Switzerland), of 6 femoral components and two complete pairings of the BHR retrieved from 8 hips were contrasted to 43 28 mm heads from second generation metal-on-metal bearings (Metasul, Sulzer Orthopaedics Ltd., Winterthur, Switzerland).

Results: After 13 months (7 to 24) the BHR femoral heads showed a median volumetric wear rate of 2.9 mm³ (interquartile range: 0.8 to 7.1), slightly, but not significantly higher than the investigated 43 28mm Metasul heads (0.8 mm³/year, p = 0.067, 14 months [7 to 24] in-situ). One BHR case with a cup abduction angle of 70° showed a significant higher wear rate of 17.8 mm³. All BHR cases showed only small amounts of metallic particle histological and correspondingly, a mild histiocytic tissue response without foreign body granuloma formation.

Discussion: During the first two years after surgery the investigated BHR components showed wear rates substantially lower than conventional polyethylene bearings, comparable to Metasul bearings, implanted with very successful clinical results. But whether the wear rates will drop down after the so called running-in period comparable to conventional metal-on-metal bearings and provide young and active patients with a biologically acceptable particle volume over a long time period, still remains to be seen.

Background: This study was undertaken to investigate the differences in the metal ion serum concentrations after implantation of a MetaSUL-THR and a Birmingham Hip Resurfacing in comparison to implant free subjects and to review the influence of factors, possibly influencing the wear behaviour of the articulation.

Methods: Serum levels of cobalt, chromium and molybdenum in 74 patients after primary implantation of a MetaSUL-THR and in 111 patients after BHR were compared with the levels found in 130 control subjects without implants. Serum ion concentration was determined by atomic absorption spectrophotometry. Furthermore, the correlation between serum ion concentration and in-situ time, implant size and cup inclination was studied.

Results: The chromium and cobalt concentrations of BHR-patients as well as the chromium concentration of bilateral MetaSUL-THR-patients, however, were significantly higher as the concentrations of patients with unilateral MetaSUL-THR and the control group. The molybdenum serum concentration was very similar in all investigated groups.

The chromium serum concentration in patients with unilateral MetaSUL-THR and in patients with BHR showed the highest level in the postoperative period from 7 to 12 months.

Analyses of the subgroups showed an association between higher cobalt serum levels and cup inclination greater than 50 in patients with unilateral MetaSUL-THR more than 12 months after implantation. A statistically significant negative correlation was detectable between implant size and chromium as well as cobalt serum concentration in BHR-patients studied more than 12 months after implantation.

Conclusions: Metal-on-metal bearings of large diameter result in a greater systemic exposure of cobalt, chromium and molybdenum ions than bearings of smaller diameter. It is not known to what extent the different levels are due to corrosion of the surfaces of the components or to the amount of wear particles produced.

The chromium concentrations were highest 7–12 months after operation, what may due to a running-in of the bearing like known from hip simulator studies.

Interestingly implant size and metal ion serum levels correlate negatively in the BHR-patients studied more than 12 months after implantation. That could be due to an existing fluid film lubrication in these bearings and may be caused by the thicker fluid film in bearings with greater radius.