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AK Amputation Options 

Knee Disarticulation Vs. Above Knee Amputation. When a surgeon decides what amputation level a patient should become there are many physiological considerations. If a surgeon determines that those considerations allow a choice between a transfemoral (above-knee) and a knee disarticulation level, the knee disarticulation may be a better amputation level to suit the patient’s functional outcome.

However, one must remember that each patient is different and a knee disarticulation may not always be an option. A knee disarticulation (sometimes called a ‘through knee’) is an amputation that involves keeping the femur intact. Instead, the tendons and ligaments attaching the femur (thigh bone) to the tibia (shin bone) are detached. There are several advantages of the knee disarticulation over the traditional transfemoral.

The first advantage is decreased rehabilitation time since there is less trauma to the femur.

Secondly, the adductor group of muscles (the muscles that bring the leg towards the body) is left intact because the bone is not cut. As a result, the patient will have more control over his/her residual limb.

The third advantage is that the end of the femur can take some weight bearing at the bottom instead of taking it entirely through the ischium (sitting bone).

The last advantage is that the length of the residual limb is as long as possible (the entire femur). More length equals more control over the prosthesis. This translates into more stability and a better gait.

The knee disarticulation level presents an interesting challenge to the prosthetist. For one thing, the end of the femur is larger than the area above it, which means it can be difficult to accommodate this area. Also, because the bone is so long it can lower the person’s knee center compared to the opposite side. Due to these kinds of challenges, few prosthetists, when consulted prior to amputation by a surgeon or patient, will recommend this level over the traditional transfemoral level. It can be a difficult level to fit unless the prosthetist has unique fitting techniques. Jason Kahle, CPO, of Westcoast Brace & Limb, has developed fitting techniques to help make the process easy for the patient and the prosthetist. One of the techniques used to create a prosthesis for a knee disarticulation patient is a dynamic evaluation interface.

The interface is made out of a flexible interface supported by a rigid frame. The interface allows the amputee and the prosthetist to try and adjust the prosthesis if necessary for several weeks before committing to finishing it. Another important factor to consider is the location of the knee center. By placing the knee more posterior and in more flexion, and by using specialized knees, a prosthetist can achieve a closer knee center.

This is unlike other traditional knee disarticulation designs. In summary, the knee disarticulation level of amputation can help increase comfort because total weight bearing on the ischium is not necessary. It can help with control by increasing the lever arm and overall length in comparison to the transfemoral amputee. It also can decrease rehabilitation time and finally, it can offer more overall stability because of the length and control of the prosthesis.

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