Osteoarthritis of the knee is between two and five times as common as osteoarthritis in the hip, and most orthopaedic surgeons accept that a knee operation can be just as successful as a hip one, if not more so. But only four knee operations are done for every 10 carried out on hips.

In 1991, 12,693 knee replacements were done in England and Wales, compared with 30,000 hip replacements. The tragedy for sufferers is that knee-joint replacements are most successful if they are carried out early. Statistics suggest only a small proportion of people are benefiting.