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Lady in her early 40's with osteoarthritis resulting from a shallow hip socket (hip dysplasia) successfully treated with an uncemented total hip replacement with a ceramic on ceramic bearing.

Sir John Charnley introduced the first successful hip replacement in the 1960's for the treatment of osteoarthritis. The damaged femoral head was removed and the hip replaced with a polythene socket and a stainless steel ball, both of which were attached to the host skeleton with acrylic bone cement.

There is no doubt that Charnley's operation has transformed millions of people's lives by relieving pain, restoring mobility and correcting deformity. Total hip replacement (THR) is one of the most successful and cost-effective operations in the whole of medicine. As experience has grown, THR has been performed on increasingly younger patients with greater physical demands for work, family life and recreation.

Patients are increasingly dissatisfied with long-term analgesic use and advice that they are too young for a hip replacement. However it is well documented that these patients' increased physical demands cause their implants to wear out more quickly and therefore need revision surgery earlier. In addition, their longer life expectancy increases the time the implant is exposed to these active conditions. Whilst the National Institute for Clinical Excellence (NICE) recommends implants which fail at a rate of 1 per cent per year, this failure rate is clearly less than ideal for patients in their 30s and 40s who will almost certainly face at least one revision in their lifetime. Charnley recognised that his metal on plastic bearing could wear out and so would not perform the operation on patients under 70 years old.

The problem with the wear process is that it is directly responsible for the loosening of implants, with subsequent renewed pain, loss of bone, and possible catastrophic failure of the whole joint. During normal activities millions of tiny polyethylene wear particles are liberated from the socket into the joint. The body's defence cells take up these particles and the cells become activated to erode bone as they cannot tell the difference between wear particles and bacteria. Over time, this can gradually destroy the foundations to which the implants are fixed, causing loosening. It therefore follows that if polyethylene wear debris can be excluded from hip replacements and the implants are effectively fixed to the host skeleton, then in theory one has a hip replacement that doesn't wear out or loosen.

Fortunately, alternative so-called "hard on hard" bearings of either metal-on-metal (MoM) or ceramic-on-ceramic (CoC) have been used in hip replacements for 30 years but have only recently become practical alternatives to the "gold standard" of metal on polyethylene. This is because modern technology has been needed to overcome the complex material and manufacturing challenges of these materials. In addition, the cup and stem designs of the early hard on hard bearings were suboptimal. Ceramics are excellent bearing surfaces, and offer a very low friction, low wear bearing surface producing very small volumes of wear particles. Ceramic bearings are coupled with conventional cup and stem designs, and so can be used in cases of poor quality bone or severe femoral deformity.

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