Abstract
Development of the metal/ metal hip resurfacing began in 1989 with the first patient implantation in February 1991. In the first three years three methods of implant fixation were employed in a pilot study of 119 resurfacings and the optimum fixation was identified as Hydroxyapatite Coated (HA) uncemented cups and cemented femoral components.
From March 1994 until February 2001 the author has performed 1503 hybrid fixed resurfacing implants, 294 of the McMinn type (HA on Smooth Metal Cup) and 1209 Birmingham Hip resurfacings (BHR; HA on Porous Metal Cup). Mean age was 52.9 years, diagnosis – Osteoarthritis 78%; Dysplasia 7%; Inflammatory 2%; Avascular necrosis 5%; other 8%. In the 294 McMinn Resurfacings 8 have failed and 7 have been revised. Reasons for failure; 5 cup loosenings, two infections and one femoral head collapse in a patient with pre-existing avascular necrosis. High wear of the metal/ metal bearings, with altered metallurgy, is now presenting as a cause for concern with these McMinn resurfacings performed in 1996 where the metal was Solution Heat Treated (SHT) and Hot Isostatically Pressed (HIP). Patients from 1996 are exhibiting asymptomatic radiographic osteolysis and at revision metallosis is seen with high wear measured on the retrieved components. Laboratory studies have shown that SHT and HIP alters the carbide microstructure and increases wear on abrasive wear testing.
In the 1209 BHR’s 7 failures have occurred requiring revision. Reasons for revision – 4 femoral neck fractures, 2 infections and 1 collapsed femoral head from avascular necrosis. Implant fixation is reliable as judged by very low migration on an R.S.A. study. Bearing wear is very low as judged from wear analysis of explants as would be expected from the historically proven “As Cast” metal microstructure. Function is good as judged by the Harris Hip Score (mean 96.3 at 3years). Cumulative survival on all Hybrid fixed implants is 97% at 7–8 years.
Hip resurfacing, using metal on metal bearings with historically proven metallurgy using hybrid fixation, offers a viable treatment alternative for the young and more active patient with hip arthritis.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
