So you think you need . . . A total hip replacement

Joint replacement is justifiably regarded as miracle surgery. The ball-and-socket joint parts of the hip, worn away by osteoarthritis, are replaced with an artificial joint made of a mix of metal and polyethylene.

Total hip replacement (arthroplasty), invented in 1962 by English country orthopaedic surgeon John Charnley, has gone on to become one of the great surgical feats of the last century. It’s now estimated that 10 per cent of people over 65 have a hip replacement, making it the most common form of surgery in the UK.

How it works

During surgery, the surgeon removes the top of your femur (thigh bone) and replaces it with a metal ball attached to a long metal stem, which is inserted into the hollow middle of the thigh bone. He then replaces the worn socket (acetabulum) of the pelvic bone – into which the rounded head of the femur fits, making up the hip joint – with a plastic or metal cup with a plastic lining.

These days, surgeons often use cementless balls in the thigh bone, relying instead on the porous metal to adhere to the bone, and manufacturers are also experimenting with metal-on-metal components (a mix of cobalt-chromium and molybdenum alloys), to avoid the wear and tear seen with plastic components, in the hope that these types of replacement hips will last longer and so be viable for use in younger patients.

The operation has become ho-hum for most doctors, who boast success rates of 98 per cent; indeed, the age at which patients are recommended for such a hip op is spiralling downward – in one recent study, the median age was 48.

What doctors don’t tell you

That 98 per cent success rate refers to the number of patients who are wheeled out of surgery alive, with the new hip intact. It doesn’t cover the casualties that occur subsequently, which can range from death to permanent lameness or lifelong illness. Particularly if you are young, you should know about these possible side-effects before you agree to the operation. If it goes wrong, you could:

* die within a few months. Hip replacement surgery trebles your risk of death. Three out of every 1000 people die within the first three months after hip replacement, most due to heart attack or stroke (BMJ, 1992; 303: 1431-5).

* develop venous thrombosis, a major risk after hip and knee surgery. The incidence of a fatal thromboembolism after surgery – when a clot, dislodged from a leg or lung vein, travels to and blocks an artery to your lungs – is 1 in 32 patients, and fatal pulmonary embolism befalls around 1 in 100 patients (Arch Intern Med, 2002; 162: 1465-71).

* experience wear debris chip-off, causing autoimmune disease. The friction caused by the metal ball rubbing against the polyethylene socket lining causes small plastic or metal particles to flake off. The body’s immune system sees these particles as foreign matter and attacks them. Since the particles typically settle near the implant, the immune system will also attack the surrounding bone (osteolysis). As bone loss occurs, the hip implant loosens and begins to function improperly. Osteolysis is considered the number-one reason for implant failure and the need for repeat operation.

The Bristol Wear Debris Analysis Team discovered in their study that particles of metals like nickel, chrome, titanium and cobalt, and even the bone cement (which contains hard ceramic particles of barium sulphate or zirconia), had worked their way from the hip joint to the liver, spleen, lymph nodes and bone marrow.

The greatest particle migrations were seen in those whose joint replacements were loose and worn, and the main problem was the matte coating used in the joint. In one patient, the level of cobalt found in his bone marrow was several thousand times higher than normal (J Bone Joint Surg, 1994; 76B: 701-12; Clin Orthop, 1999; 369: 92-102). In one Frenchman complaining of weight loss and fatigue, wear debris had travelled into his spleen and liver eight years after surgery (N Engl J Med, 1996; 335: 133).

* have the hip dislocate, either immediately or later, requiring repeat surgery (Curr Opin Rheumatol, 1994; 6: 161-71).

* end up with one leg appreciably shorter than the other. Cleaning out osteolysis can leave that leg as much as two to three inches shorter than the other (Curr Opin Rheumatol, 1994; 6: 172-6). This may happen in any case as, in order to stabilise the hip so that it won’t dislocate, many surgeons deliberately make one leg a bit long or short.

* need to have your artificial hip eventually replaced with a new one. After 10-15 years, your hip will be worn and need a ‘revision’ – a replacement hip joint. This is a far more formidable operation, requiring the removal of more bone and tissue, and has a far lower success rate. If you are under 60, you face having to undergo several more revision operations in your lifetime.

* suffer damage to the sciatic nerve, the large nerve that runs down your leg. Repair surgery has a poor success rate.

* develop cancer near the implant site. Two studies have shown an association between cancer of the lymph nodes or leukaemia and hip replacement (J Bone Joint Surg, 1992; 76B: 539-42, 701-12).

Lynne McTaggart