The high failure rate of hip replacement surgery is chiefly caused by poor-quality implants with no long-term record
If your own hip has worn out, an artificial joint could change your life, freeing you from pain and restoring mobility - but not if it crumbles within a few years. According to a recent report from York University, many hip implants do not last; the result, for the patient, is further pain and distress, and yet more complicated surgery. What is going wrong?

Hip replacement is one of the most common major operations, with about 40,000 carried out on the NHS each year and a further 11,000 performed privately, usually on old people whose joints have become stiff and painful. The operation involves cutting through the surrounding muscles to expose the hip joint and removing the top of the thigh bone, or femur. A hole is then cut in the remaining bone, for a cup-shaped socket - one part of the artificial hip joint - to fit into. The ball part of the new joint is inserted into the cup-shaped part and the components are fixed in place, sometimes with special cement. Muscles and tendons are repaired, and the incision closed. Recovery normally takes a couple of weeks.

Providing all goes well, an artificial hip joint can greatly improve quality of life, with a dramatic reduction in pain and increase in mobility. The trouble is that all does not always go well: operations to replace faulty implants now make up about 11 per cent of all hip replacement surgery; some specialists predict that the figure could rise to 25 per cent. "Revision" ops are more complicated than the initial operation and have a poorer success rate.

The high failure rate of hip replacement surgery is chiefly caused by poor-quality implants. The York report, produced by the NHS Centre for Reviews and Dissemination, points out that surgeons have 62 types of artificial hip joints to choose from, manufactured by 19 companies and ranging in cost from pounds 250 to pounds 2,000. Half of those models have been introduced since 1990, so there is little evidence of their long-term effectiveness. Only a handful have been shown to last for any length of time, and most have never been properly evaluated. One study, published in 1995 by the Nuffield Orthopaedic Centre in Oxford, which looked at the evidence for all 62 implants on the UK market, found that only 30 per cent had featured in any results published in a serious scientific journal.

Why do we need so many different models? Possibly because surgeons like experimenting; but more probably because older models are less profitable for the manufacturers than hi-tech modern ones.

Which is a pity, because it's the oldest, cheapest models that seem to last longest. According to the York University report, only two models, the "Charnley" and the "Stanmore", have enough long-term evidence to support their use. Studies have shown that 80-90 per cent of patients had no problem with those basic models (or updated versions of them), for at least 10-20 years' follow-up. Both models use cement, a factor which, the report says, is associated with a better outcome.

But success or failure is not just a matter of the quality of the implant. Surgical skills are also crucial: hip replacement operations by a trainee surgeon are more than 11 times more likely to need revisions than those carried out by a consultant, according to a 1996 study (although, on the other hand, some so-called "trainees" may have more experience in hip replacements than a consultant). Studies have also shown, unsurprisingly, that hospitals with a higher volume of joint replacement surgery have lower rates of mortality and fewer post-operative complications.

Anyone facing hip replacement surgery would do well to discuss with their consultant the track record of the type of implant to be used - as well as that of the doctor who is to perform itn

Cherrill Hicks