Hip replacement | Artificial hip joint
Methods | Components | Fixation | Material and tolerability | Service life | Surgery | Consultation
WHEN DO I NEED AN ARTIFICIAL HIP?
If the pain is defining your life and no clear improvement of the hip problems has occurred despite conservative treatment, it is time to consider a joint replacement or artificial joint.
The implantation of an artificial hip joint (hip replacement) has the goal of restoring freedom from pain, movement and mobility. However, an artificial joint can never fully match the perfection of a natural joint. There are artificial hips in various sizes and different materials.
Thanks to the well developed, tissue-preserving keyhole surgery method whereby the artificial hip is implanted minimally invasively from the front, the stabilising muscles of the hip are simply pushed to the side and not cut through, as previously. An incision in the skin of around eight centimetres is enough to fit the artificial hip.
WHAT ARE THE ADVANTAGES OF THE SOFT-TISSUE-ORIENTED METHOD?
There is significantly less pain after the surgery as the muscles are no longer injured with this technique. Thanks to the tissue-sparing procedure, the loss of blood is also relatively small. Thus the previous requirement for an autologous blood donation is no longer required.
The artificial hip has four components. Two of these are directly connected to the bone: the hip socket with the pelvis and the shaft with the interior of the femur. The new femoral head and the lining of the hip socket (called the inlay) form the new cartilage.
The artificial hip shaft is anchored strongly inside the femur. This is possible as the femur is hollow on the inside (a long bone). The upper part of the shaft forms the new neck of the femur and has a cone which attaches to the new artificial head of the femur. There are various models of hip shafts which differ in length (prostheses with short, standard or long shafts and revision prostheses). The hip shaft model which is best suited is decided dependent on the personal situation, age and bone quality.
The head of the new artificial hip joint forms the new artificial cartilage for the head of the femur. This can be either ceramic or metal (steel). The diameter of the head is normally between 28, 32 and 36 millimetres. The surface of the head is highly polished so that it can move well and with little friction within the new hip socket.
The double-mobility femoral head is a special form. In this case, there is a further, smaller, mobile head inserted into the head of the femur. This gives increased stability and a lower risk of the hip joint dislocating. The double-mobility femoral head is used in elderly patients and those with neurological disorders to reduce the risk of the dislocation of the operated hip joint through an incorrect movement.
The artificial socket is fixed in the natural socket in the pelvis and completely replaces this. There are also different models of socket. Different socket models are used depending on the individual situation and bone quality.
The inlay forms the new artificial cartilage for the artificial socket. The inlay is fixed within the corresponding socket with an optimal fit to the new femoral head.
There are two different methods for fixing the artificial socket and shaft into the bone: with or without cement. There are also mixed forms - called hybrids - where the socket is cemented and the shaft is cement-free, or vice versa. The form of fixation depends on the bone quality of the femur and pelvis. This can only be assessed in part during the surgery, hence changes to the planned surgical procedure are possible at short notice.
Cement-free or uncemented fixation
In cement-free fixation, the artificial hip socket or shaft is pressed firmly into the corresponding bone after it is appropriately prepared. The artificial socket and shaft are specially coated so that the bone can grow into them quickly. Despite this coating, it takes six weeks on average until the bone has merged with the new artificial socket or shaft to provide a stable bond.
If the quality of the bone is not optimal, the bone brittle or osteoporosis is advanced, the artificial hip socket and shaft are fixed in the prepared bones with bone cement. The bone cement hardens rapidly, creating a solid bond between the artificial material and the natural bone. In addition, the cement can be premixed with antibiotics which are then slowly released around the implanted prosthesis, reducing the risk of infection. The cemented fixation method rapidly allows full weight-bearing of the operated hips.
We always strive to use contemporary and innovative materials which are not only well tolerated but also highly resistant to corrosion and/or show little mechanical wear.
The metal components fixed to the pelvis or femur are made of titanium or steel. Steel is a mixture of various metals such as cobalt, chrome, molybdenum, iron, manganese and nickel.
Wherever possible, we use cement-free fixation of the socket and a shaft made of titanium. Titanium is the best tolerated metal in humans: no allergies to it have been reported. If the shaft or socket needs to be cemented owing to unstable bone quality, we generally use a shaft made of steel and a plastic socket. The disadvantage of this is that there can be allergic reactions to the cement itself or to individual metallic components released from the steel.
The artificial cartilage of the new hip joint is found on both the femoral head and on the inlay - also known as the socket inlay. Where possible, we use ceramic products for this. The ceramic-ceramic glide pairing has the advantage that it causes no abrasion. Other glide pairings such as metal-metal or metal-plastic cause abrasion and can lead to inflammatory reactions, pain or early loosening of the artificial joint. Metallic abrasion can lead to metallic components entering the blood, leading to the poisoning of other organs such as the kidneys, liver, intestines, etc. We therefore usually use the ceramic-ceramic glide pairing and, in rare cases, ceramic-plastic (ultra-high molecular polyethylene).
Even if one could wish that the new artificial hip would last a lifetime, it must be recognised that the artificial hip is always a temporary solution. This can be caused by the wearing of the glide pairing, especially if plastic or metal were used, or by the natural ageing process (osteoporosis) which can have a significant effect on the stability of the artificial joint.
The average service life of an artificial hip is currently at least 10 to 15 years. The tissue-sparing surgical method and the materials available today (e.g. a ceramic-ceramic glide pairing) assure us that the service life of an artificial hip has increased significantly. This is always provided that infections, falls resulting in bone breakages or rapid progression of the osteoporosis do not cause the artificial hip to fail early.
Everything you need to know about hip surgery or artificial hip implants can be found here.
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