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.

Question: Is the histopathological response of the peri-prosthetic tissue to metal-on-metal bearings comparable to the well studied reactions to polyethylene debris or do specific reactions exist and are theses reactions depending on the implant design?

Methods: Periprosthetic tissue samples from 19 THR and Hip Resurfacings (11 Birmingham Hip Resurfacings, 2 (historical)McMinn Hybrid Hip Resurfacings, 5 MetaSUL THR) with a variety of failure mechanisms were examined histopathologically and immunohistochemically.

Results: Only the samples of the (historical) McMinn Hybrid resurfacings showed a stronger histiocytic foreign body reaction and a higher grade metallosis. In all other cases only a mild if any histiocytic foreign body reaction was found. Additionally a chronic lymphoplasmacellular tissue reaction was present in all cases. 3 cases showed a higher grade chronic lymphoplasmacellular inflammatory tissue response comparable to a specific immune reaction.

Discussion: We found two different response mechanisms of the periprosthetic tissues to metal-on-metal bearings. In addition to the classic histiocytic foreign body reaction which was usual mild and only stronger in cases with a greater amount of metallic debris a lymphoplasmacellular inflammatory reaction usually was present but did not reach the level of inflammatory alterations associated with potential osteolysis and was not related to the implant or amount of wear. In 3 of our 19 cases the lymphoplasmacellular infiltration was stronger and comparable to a specific immune reaction. The significance of the specific immune reaction could not be further explained because a correlation to the failure mechanisms was not detectable

Aims: Do the short term results, histopathological þndings and metal ion concentration predict a better outcome of modern metal-on-metal Hip Resurfacings (BHR) in comparison with historic metal-on-polyethylene Resurfacings? Methods: Comparison of 241 BHR arthroplasties with a follow up from 6 months to 4 years with long time results of 305 WHR; of 7 BHR and 3 MetaSUL capsule tissue histologyñs and chromium and cobalt serum concentrations of 67 BHR patients and 32 patients after MetaSUL THR implantation. Results: We achieved mean Harris Hip Scores of 90–92 in our BHR series with no radiological signs of aseptic loosening and a revision rate of 1.7% after approx. 18 months in opposition to 8% of the WHR after 2 years. The BHR capsule tissue showed wear particles in only 2 of 7 cases in opposition to MetaSUL joints, where in every case wear particles were detectable. We found no statistical difference in metal ion serum levels between BHR and Meta-SUL joints. Conclusions: In our opinion the cementless press þt cup, the low wear metal-on-metal bearing and the conservative implantation technique of the BHR at least fundamentally improves the known disadvantages of the historic Resurfacings which may predict better long term results.