New joints for old

George Morris Physio Wigan

New joints for old

Knee Replacement

There are 150 types of knee prostheses, and each comes in 20 or so sizes — and each of those may have two or three different widths to achieve a perfect fit.

There are three areas of the knee — the inner (medial), the outer (lateral), and the kneecap (patellofemoral).

During the operation, the worn ends of the thigh bone and top of the shin bone, and any remaining hard cartilage (most of which will have been worn away by arthritis) are removed and replaced with the artificial joint, which includes a spacer — made of plastic and put into the middle to act like hard cartilage — to help the joint, made of titanium or chrome cobalt, to move freely.

Around 6.4 fail after 15 years and need more surgery, but most should last 20 to 25 years, says Mark Wilkinson, a professor of orthopaedics at the University of Sheffield.


With around 109,000 procedures carried out a year, hip replacements are the second most common joint replacement surgery.

These implants have three parts: the stem, fitted into the top of the thigh bone; the femoral head, made of metal or ceramic, that moves in the hip socket; and the cup or socket, made of metal or hard-wearing plastic, which goes into the pelvic bone.

The most commonly used implants are metal-on-plastic — a metal stem with a plastic ball and socket joint.

'Most of the metals contain nickel, so if you have a severe nickel allergy, tell your surgeon as an alternative may be needed,' says Professor Phil Turner, a knee surgeon at Stepping Hill Hospital in Stockport.

There are dozens of brands of hip implants, which come in different sizes to match the patient.

The procedure takes around an hour, normally under a local anaesthetic in the spine and, as with knees, the artificial joint can be fixed with or without cement.

Age is a good indicator of whether cement is used.

Cemented hips are better for older people because they provide more stability for their weaker muscles, and are less likely to fracture.

Hip replacements have a failure rate of 7.82 per cent after 15 years.

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