My 87-year-old mother-in-law fell over in the lobby of her care home last month, shattering the top of her thigh bone. The next day, in a two-hour operation, she was fitted with a replacement. Two years ago, my friend Anna underwent a full hip replacement; then in her early fifties, she had been suffering increasing pain from osteoarthritis in her left hip.

My mother-in-law and Anna represent opposite ends of the same spectrum: a steep rise in the demand for hip surgery driven by, at one end, an ageing population and, at the other, a generation of physically active men and woman in their forties and fifties who refuse to put up with pain and restricted mobility. New figures predict that the number of hip operations will more than treble in the next 20 years, requiring the training of many more orthopaedic surgeons, with huge implications for the nation's health budget.

Anna was 54 when a consultant at the end of a hard day in clinic told her that she needed a hip replacement. She was shocked: she was too young, she protested, it could wear out after ten years and she would have to face more major surgery. “The consultant looked at me with cold, tired eyes,” she recalls. “He said, ‘You could be dead from bowel cancer in ten years'. It was a bit brutal, but the message was clear: seize the day.”

The message is a relatively new one: until recently patients under 60 suffering the joint pain and physical constraints typical of osteoarthritis were told to go away and live with it. The concern was that younger patients would outlive their implants and need one or even two revisions - a more complex procedure than primary arthroplasty - over their lifetime. “The technology for revisions was not so good,” explains Roger Gundle, a consultant at the Nuffield Orthopaedic Centre in Oxford. “It was a law of diminishing returns: the second hip replacement wouldn't last as long as the first and so on.”

Techniques have improved and surgeons are more confident, he says, enabling them to meet more readily the demands of the baby-boomer generation who want to go on dancing, playing tennis and hiking up Machu Picchu. “Now we are seeing many more younger patients who just won't accept the limitations imposed by their condition,” says Gundle. They may also have exercised themselves into an early appointment in the orthopaedic clinic - all that Jane Fonda “feeling the burn”, step-aerobics and road running has taken its toll so that those with a predisposition to arthritis may develop it sooner than their parents and grandparents did.

Martin Richards has been sports-mad all his life, playing five-a-side football, tennis, squash and badminton. At 50 he tried taking up waterskiing but found that he couldn't crouch down to pick up the tow handle; if he fell he had difficulty getting up again. “I would lie there like a beached whale,” he says.

He thought he probably had a groin injury, but pain and difficulty moving got worse, he put on weight and eventually X-rays showed advanced osteoarthritis. “Your hips are shot,” a consultant told him. “I went away, lost 2st (12.7kg), then came back for the operation. A year later I had the other hip done.”

Richards was soon back playing all his favourite sports, fishing and camping. At 57, five years after surgery, he says that he feels fantastic: “It was a total life change. I feel very lucky.”

Richards underwent a procedure called hip resurfacing, invented ten years ago in Birmingham by the orthopaedic surgeon Derek McMinn and named the Birmingham Hip, though there are now many imitations. Instead of removing the head of the thigh bone and replacing it with an artificial ball (hip replacement) a hollow metal cap is fitted over the head of the thigh bone, which corresponds with a metal casing inside the hip socket. The procedure is now recommended by the National Institute for Health and Clinical Excellence (NICE) for younger and more active patients though not all orthopaedic surgeons agree about its role. “Some see it as a holding operation,” says Jane Tadman, of the Arthritis Research Campaign, “postponing the day when a traditional hip replacement will be needed. Others claim it is a perfectly good - and less invasive - procedure in its own right.”

Because resurfacing is a relatively new technique, there is little data on outcomes, though early reports suggest a success rate of more than 95 per cent at five years after surgery. In one trial, hip resurfacing performed better in young active patients than total hip replacement. But the materials used were different - metal on metal for the resurfacings, metal on polyethylene for the replacements - and it may be that if the more expensive metal or ceramic bearings were used, the replacement would perform better.

“Hip resurfacing has been well marketed,” says Tom Pollard, an orthopaedic specialist registrar. “But it is not yet certain that it is superior to total hip replacement using comparable materials in the longer term.”

Martin Richards was told that his new hips should last about ten years, though he admits he probably does too much. “They may wear out before then.” He says that it's important to be a good weight before and after surgery, and you have to work hard to regain fitness: “I couldn't have done it without the support of physiotherapists at my local hospital. If I can get to 60 with these hips, swimming, playing tennis and squash, I'll have had a good run.”

Richards may need total hip replacement if his resurfacing fails, but one advantage of resurfacing is that this is usually a straightforward procedure compared with revision of a primary total-hip replacement.

Helen Cotterell was only 42 when she began to feel pain in her knee that increased in intensity over the next six years and osteoarthritis was diagnosed in her right hip. “My GP told me: ‘Oh you're miles off a replacement'.” A friend recommended her to see a consultant privately who gave her a year before she would need surgery. “When I went back, I'd worn another quarter of an inch off the bone.” Resurfacing was recommended because she was so young: “He said it could stand one or possibly even two revisions before I would need a full replacement; he reckoned he could get me through into my nineties.” Even so, Cotterell was uncertain: “Do I really need this op?” she asked. “You tell me,” said her consultant. “I thought, yes, I want to climb mountains with my kids, who were only 10 and 13 at the time, I want to keep up Scottish reeling, I don't want to limp down Oxford Street and sit in agony like an old woman in Topshop while my daughter tries on clothes.”

After a second operation on her other hip, Cotterell went to a remedial masseuse: “She taught me how to walk properly - swinging each foot forward like a catwalk model rather than waddling, which I'd got used to when the hips hurt.” She has no idea why the disease struck her so young: “My grandfather had a hip replacement at 70 but he was crippled by then. They were more stoic, that generation, weren't they?”

It is now two years since my friend Anna's hip replacement and the joint is still “miraculously” pain free. “I was tremendously grateful,” she says. “But unprepared for the extent of my disability when I got home. My husband had to put my support stockings on for me. I hated the helplessness and felt frightened and furious.”

When she went back for her postoperative check-up, Anna told her consultant that it would have been helpful if someone had prepared her for the psychological impact of surgery. “He said, ‘You were in pain; now you're not in pain. Be grateful'.” She laughs: “It was so reductive. But they're engineers, these guys, there's not much hope of having your neurotic sensibilities catered for.”

Early screening will pick up signs of those at risk

Twenty and thirtysomethings today who go on to develop osteoarthritis in middle age are likely to be offered a range of treatments before they need to contemplate hip replacement - already considered very much end-of-disease salvage surgery, says Jane Tadman, of the Arthritis Research Council, which funds research into new therapies such as tissue engineering.

“This takes patients' own healthy cartilage cells, grows them on a scaffold in the lab and then re-implants them into areas of damage,” she says. “If trials are successful, tissue engineering could become the routine means of, if not preventing, then slowing down cartilage degeneration - one of the major components of the disease process.”

John Fisher is professor of mechanical engineering at Leeds University: “In 20 or so years' time, while conventional joint replacement will still exist for patients of 65-plus, there will be advanced interventions such as tissue engineering for younger patients,” he predicts. “The concept of a continuum of care with personalised therapy plans will exist, with a series of minimally invasive sequential interventions over 30 or 40 years, perhaps ending with joint replacement.”

Early screening, imaging and genetic testing will pick up patients most at risk. Traditional hip surgery leaves an 8in or 9in (20cm or 23cm) scar, but already a small percentage of procedures are done using microsurgery techniques in which the incisions are much smaller and the procedure is less invasive, with less muscle damage and a shorter recovery period.

Meanwhile, bio-engineering firms competing in a global implant industry worth £5 billion a year are working to improve the material from which bearings are made and their coatings. Wear on bearings and particles chipping off resulting in loosening of the joint is the main reason for revision surgery.

All you need to know about hip replacement

What is osteoarthritis? A common condition where the cartilage becomes thinner and damaged and extra bone forms at the edges of the joint. It can result from abnormal stress on the joints, or from many different forms of injury or joint disease. However, most cases develop without any obvious reason.

What can be done? Initial therapy may involve weight loss, orthotics, walking aids and physiotherapy. Ultimately, the patient may need a total hip replacement where the top of the thigh bone is sawn off and a cone-shaped shaft drilled into the bone. A steel pin with a ball shaped, metal or ceramic head is inserted and fits into the hip socket, which is lined in metal, ceramic or polyethylene. Replacements last between 15 and 20 years. An alternative is resurfacing: the top of the thigh bone is smoothed off and fitted with a mushroom-shaped metal cap; the socket is also lined in metal.

What's right for you? Surgeons take into account fitness, age and patient expectations when deciding on a procedure. Patients over 65 will usually have a hip replacement made of metal and polyethylene, which should last the rest of their lives. Younger and more active patients will have resurfacing or a total replacement made of metal or ceramic, and both are expected to last longer.

How do you qualify? If joints give pain at night and/or pain limits function and doesn't settle with more conservative therapy. Patient demand is also taken into consideration.

How long will you have to wait for hip surgery? The NHS target is now 18 weeks from referral, which many orthopaedic services find “challenging”.

What are the risks? Infection after arthroplasty can mean the whole procedure needs to be done again as antibiotics are not good at getting to bugs beneath artificial bearings. However, infection occurs in only 0.5 per cent of cases. Deep-vein thrombosis leading to pulmonary embolism occurs in one case in 300. Dislocation sometimes occurs if patients don't observe a fairly strict, six-week postoperative regimen. The risk of femoral fracture is higher with resurfacing than with replacement. Resurfacing is often not advised for postmenopausal women who may have thinning of the bones. Metal prostheses should be used with caution in women of child-bearing age, because metal ions are released into the blood from the joint and it is not known what effect these may have on the foetus.

How long to recover? It varies between patients, but six weeks is the average time for rehabilitation and improvement continues for up to a year.

What is the cost of going private? Between £6,000 and £8,000 depending on the procedure and materials used. Around 50 per cent of private patients are covered by health insurance; the rest pay for themselves.

The Arthritis Research Campaign: 0870 8505000; www.arc.org.uk

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