[Reasons for failure of hip resurfacing implants. A failure analysis based on 250 revision specimens]

Hip resurfacing has been experiencing a revival over the last 5-10 years. Early failure rates are higher than for conventional primary hip arthroplasty. Fractures of the femoral neck or head, cup loosening and persistent pain are the most frequently observed reasons for early revision. In this international retrospective uncontrolled study, 256 revision specimens (219 resurfacing heads, 37 cups) were analysed radiologically, tribologically, morphologically and histologically in order to investigate the failure mechanism. Of the head revisions, 70% were due to neck (median: 67 days after implantation) and head fractures (161 days), 9% were due to cup loosening (350 days) and 21% due to other reasons (602 days). Implants with rim loading (22% of all retrievals, cup inclination 58.0+/-10.9 degrees ) exhibited a head wear rate of 7.1+/-5.2 mm3/year. Non-rim loaded implants exhibited a head wear rate of 0.24+/-0.53 mm3/year (cup inclination 49.0+/-4.0 degrees ). The failure rate was highest during the first 16 weeks after surgery and for the first ten operations performed by a surgeon. Revisions based on problems on the femoral side such as notching and high implantation forces occurred earlier than revisions based on problems on the acetabular side such as cup loosening and high wear due to suboptimal cup position.