A hip prosthesis (artificial hip) is placed in the event of serious damage to the hip joint. The cause of this damage is usually arthritis or a rheumatic disease. This causes pain and impaired function. The damage can be seen on an X-ray of the hip and is confirmed by functional tests.
The hip joint consists of the head of the thigh bone that rotates smoothly in the socket of the pelvis. This smooth movement is made possible by a layer of cartilage at the head of the femur and in the socket of the pelvis. Cartilage is a smooth and springy tissue.
Wear and tear of the cartilage is called osteoarthritis. Such wear and tear is a normal aging process that occurs in everyone. In some people however, the wear and tear progress faster. Causes are abnormal load, an accident or malformation of the hip joint. There is certainly also an important hereditary factor. Wear and tear is not always due to a specific cause.
Wear and tear cause pain. If the pain can no longer be relieved by other means, a hip prosthesis will be suggested. In case of severe hip damage, both the ball of the hip and the socket are replaced (full prosthesis).
In some cases, we also place a prosthesis if the hip head breaks off. In this case it is not always necessary to replace the entire joint. Usually only the broken off head of the thighbone is replaced. We then speak of a half prosthesis or hemi prosthesis.
A hip prosthesis is an imitation of the normal hip. In the operation, the ball of the hip is removed and the remaining cartilage in the socket is milled out (see Illustration B).
Then the components of the new hip are inserted. The new socket is made of plastic and metal. Then a metal pin with a small head on top will be inserted into the thigh bone. This fits exactly into the plastic socket. This pin is also called the stem or voice.
There are different ways of securing the parts. Our orthopaedists usually clamp the metal socket into the original hip socket. This way, the bone grows into the prosthesis. This growth is achieved after about 6 weeks. Sometimes one or two screws are inserted to ensure extra firmness.
In the metal socket a plastic component is placed that is traditionally made of durable plastic.
The metal stem consists of titanium and can be placed in two ways:
The stem can be fixed in the thighbone with special cement (methyl methacrylate). Here, too, a firm anchoring must be achieved through the growth of bone; as mentioned earlier, this requires about six weeks. On the other hand, the metal stem can be clamped into the femur, without the use of cement. Whether cement is used or not depends on the quality of the bone and the age of the patient.
The lifespan of the hip prosthesis is on average between 15 and 20 years.