Commentary: Metal on metal hips

Total hip replacement is one of the most successful operations of the 20th century and is currently performed in 70 000 patients a year in the UK,1 250 000 a year in the United States, and one million worldwide. In an attempt to improve wear resistance and to allow bone conservation through hip resurfacing, metal on metal bearings were re-introduced in the 1990s.2. These are made of cobalt chromium alloys, and in some series metal hip resurfacing has shown excellent results in the younger and most active patient groups.3 Several other designs were introduced, and hip resurfacing became popular with patients through the internet as a younger person’s solution to arthritis that allowed high activity levels. It was used in 10% of hip arthroplasties in the UK between 2006 and 2009 and in 50% of all hip replacements in patients younger than 50 years.1

Problems with hip resurfacing that were initially reported included raised blood cobalt and chromium ions,4 loosening of components,5 hip fracture,6 and soft tissue reactions around the hip.7 In an attempt to overcome the fracture problem and to extend the use of large diameter metal on metal bearings to those not suitable for hip resurfacing, metal resurfacing type bearings were introduced on total hip replacement stems.8 These large diameter metal on metal total hip replacements had a lower theoretical rate of dislocation. In fact, metal on metal bearings were used in up to 35% of all total hip replacements in the United States in 2009.9

The commonest symptoms of adverse reactions to metal debris are pain, swellings around the hip, …