HIP REPLACEMENT SURGERY

WHEN DO YOU NEED A HIP PROSTHESIS

An artificial hip is placed in case of serious damage to the hip joint. This damage is usually caused by osteoarthritis or a rheumatic disorder which causes pain and malfunctioning. The damage can be seen on an X-ray of the hip and has to be confirmed by functional tests.

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The hip joint consists of the head of the thighbone (the femur), which rotates smoothly in the pelvic bowl or acetabulum. This smooth movement is made possible by a layer of cartilage on the head of the thighbone and in the bowl of the pelvis. Cartilage is a resilient and smooth elastic tissue. Wear and tear in cartilage is called osteoarthritis.

Such wear is a normal ageing process that occurs in everyone. Some people are affected faster by wear and tear, than others. This can be caused by abnormal strain, an accident or deformations in the shape of the hip joint. There is certainly also an important hereditary factor. Wear and tear cannot always be attributed to a specific cause.

Such attrition causes pain. When the pain can no longer be remedied by other means, a hip replacement will be suggested. In case of serious hip damage, both the head and hip bowl of the hip are replaced (full prosthesis).

We also often implant a prosthesis if the head of the hip breaks off. In that case it is not always necessary to replace the entire joint. Usually only the broken head of the femur is replaced. This is referred to as a ‘half prosthesis’ or ‘haemiprosthesis’.

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WHAT DOES A PROSTHETIC HIP LOOK LIKE?

A prosthetic hip is an imitation of the normal hip. The ball-shaped head of the femur is removed during the operation (figure A). The remaining cartilage is removed from the socket. (figure B)

Then, the parts of the new hip are set into place. They will insert a bowl of plastic and metal in the hip socket (figure C). Then a metal pin is placed in the upper leg with a small cup on top (figure D). This fits exactly in the plastic bowl. This pen is also called the stem.

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There are several ways to secure the components. We usually simply clamp the metal bowl into the original hip socket. The bone grows into the prosthesis. This in-growth is achieved after approximately 6 weeks. Sometimes one or two screws are placed to ensure extra strength.

A plastic part is placed in the metal bowl that is traditionally made of durable plastic.

The metal stem consists of titanium and can be placed in two ways.

Either the stem is fixed in the thigh bone with special cement (methyl methacrlylate). Here, too, a firm anchoring must be achieved by the ingrowth of bone. As mentioned before, this will take about six weeks. Either the metal stem is clamped into the thighbone, without the use of cement. Whether or not cement is used depends on the quality of the bone and the patients’ age.

We expect the life span of the prosthetic hip to be 15 to 20 years.