KNEE REPLACEMENT SURGERY IMPLANT FIXATION METHODS

There are four ligaments that will ensure the knee joint works correctly. Their job is to assist hold the bones in place. When the knee is sound then they are very effective. However, when a knee joint deteriorates, say due to joint disease, damage and scarring can develop to these ligaments. The objective of knee replacement surgery is to replace some or all of these ligaments and also the surfaces of the knee joint by synthetic components or prostheses. These prostheses need help to stay in place and two types of implant fixation techniques can be used – cemented or cementless.  With both methods knee rehabilitation exercises to help speed up recovery are important.

CEMENTLESS FIXATION METHOD

Cementless fixation was first unveiled in the 1980′s and entails making use of implants whose surfaces are attractive to new bone growth so that they would attach to the bone without using any kind of cement or adhesive. In other words the new bone grows into the specially coated surface of the implant. Cementless implants do require using screws to aid the stability of the implant until the new bone grows sufficiently to provide adequate support. Because it is essential to wait for the new bone to grow into the implant and because of the use of the supporting screws, recovery time is more lengthy than if using a cemented fixation technique. Even though this procedure has proved as effective as cemented fixation in many cases, it has not solved the problems a result of bone reduction and wear in the implant (see below).

CEMENTED FIXATION METHOD

The most common method these days is cemented fixation in which a polymethylmethacrylate cement, a special fast curing bone cement, is used to hold them in place. Knee replacements performed using this method have had excellent outcomes with an expected life of 15 to 20 years. In the other method, cementless fixation, the actual bone is encouraged to actually grow into the surface of the implant.  Bone reduction and wear of the implant is also an issue with this method.  Nonetheless, despite these issues, which are rare but not unknown, cemented fixation has turned out to be to be a most reliable technique in total knee replacement in most cases including in young patients who have an energetic lifestyle and where joint disease was relatively advanced.

ISSUES

How long a knee replacement lasts and how well it functions are determined by the overall health and weight of the recipient as well as the amount of use the knee joint gets and the stresses placed on it by this use. Weight management is very important in reducing wear and in lessening the risk of other conditions.

When orthopedic knee replacement surgery is carried out, the harder bone at the top of the tibia or shinbone is removed. The softer more porous bone that is left must absorb the stresses that your knee joint is put under, which under normal use can be considerable. If these stresses are greater than this bone is capable of absorbing then the metal alloy components of the prosthesis can loosen. Over a period of time, these kinds of excessive loads may well cause the prosthesis to sink into the softer bone tissue or loosen its adhesion to the bone.

Loosening of the prosthesis and sometimes bone reduction can be a result of the polyethylene layer between the metal components wearing unevenly. This may be caused by an uneven gait where by the knee is subjected to uneven loads leading one side of the knee implant to push into the bone whilst the other side lifts off from the bone. This uneven wear may also cause tiny particles of the polyethylene layer to rub off. This “debris” may cause the body to set off a biological reaction that could cause further movement of the knee implant. Bone loss may also be a direct result this. What happens then is that the surrounding cells absorb these minute particles. The body’s immune system senses this and attempts to eliminate them by triggering an inflammatory response. This response may also cause osteolysis, a condition where the cells essentially take away some of the bone from around the prosthesis. As wear increases so does the bone loss and the weakened bone causes the implant to loosen more.

CONCLUSION

It seems that both methods are successful in total knee replacement surgery. Having said that, the use of cementless implants has only been relatively recent and so long term comparisons of the two methods are unavailable but in the short term, it would seem that the success rates are comparable.

Technorati Tags: implant fixation techniques, joint disease, knee replacement surgery, orthopedic knee surgery, total knee replacement surgery

Tags: implant fixation techniques, joint disease, knee replacement surgery, orthopedic knee surgery, total knee replacement surgery

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