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Through Knee Amputation

Your leg has been amputated through your knee joint, leaving your femur intact. More energy will now be required to mobilise than a below knee amputee, however the functioning hip joint and complete femur will be of a great advantage in powering and balancing on the prosthesis. There are a few more components needed than a below knee prosthesis. Your main components that will be required are a comfortable socket, a suitable prosthetic knee and a prosthetic foot.  

The need for a Through Knee amputation may be as result of one of the following conditions:

  • Peripheral vascular disease (poor circulation) 
  • Diabetes
  • Infection
  • Foot ulcers
  • Trauma causing the lower leg to be crushed or severed
  • Tumours

What is a Through Knee Amputation?

Whenever an adequate below knee residual limb cannot be obtained, a through knee, also known as a knee disarticulation, is the next procedure of choice. The procedure causes less shock than amputations through the thigh as there is less surgical trauma to the bones and muscles. The circulation in the thigh is preserved, to supply skin flaps which are accustomed to pressure. 

As your femur and muscles are not cut the spread of infection is minimised, and the stump heals rapidly. When the patellar tendon has been fixed distally, patellar pain and swelling have not resulted in significant problems. The large surface of the bottom end of the femur is available to provide for weight-bearing. The stump is usually firm and insensitive. There is less atrophy of the muscles in the stump than after amputations at a higher level and, because of this, earlier fitting of a prosthesis is possible. The shape of the stump provides greater balance and stability without rotation compared to that of stumps in higher level amputations.  

Through Knee Amputation – some positives

While an amputation is never ideal, there are some positives when it comes to a through knee amputee.  

  • Body weight is taken on the bottom of the stump which is usually relatively comfortable and most through knee amputees report that they get used to the pressure very quickly. 
  • The prosthesis for such stumps is easier to construct and to fit, requires fewer adjustments, and is superior in comfort and function to prostheses for higher levels of amputation through the thigh.
  • Without a prosthesis the patient can kneel in work or play, as weight bearing is possible on the end of the stump.  
  • A Through knee prosthesis is challenging to use at first but with training independence from assistive devices such as crutches can be achieved after 4 to 12 weeks of receiving the prosthesis. 
  • Swimming, running, returning to sports are all possible depending on your physical condition and your prosthetic components. 

The Socket

As with all prosthetic sockets, the fit is extremely important. A Through Knee socket is custom made according to the shape and size of the residual limb. The prosthetists expertise come into the design and understanding of your unique needs. The prosthesis is suspended by various methods that will be discussed during your assessment. The socket design is unique to you. It is important that you discuss with your prosthetist any concerns or explain as best as you can where you are feeling pain or discomfort in your socket. You are the one wearing it and you need to be comfortable in it. 

The prosthesis is suspended by various methods, these methods will be discussed during your assessment. The main suspension method is a vacuum (active or passive) system. It is usually not possible to use a pin lock system in this prosthesis as it will lower the centre of rotation of the knee as your stump is already very long. The centre of the knee joint in this type of prosthesis isn’t symmetrical with the other leg, this is due to the thickness of the components such as the liner, socket and the types of prosthetic knees available. Weight-bearing is distributed over the entire surface of the residual limb and the femoral condyles. Your prosthetist will advise you on the socket manufacturing method they recommend based on your specific needs. The liner used for suspension is soft “sock” that is rolled on to your residual limb to form a soft and protective layer between your residual limb and the socket, these liners are either silicon, gel or polyurethane. 

The Prosthetic Knee

The prosthetic knee joint allows both flexion (bending) and extension (straightening) and varies in function depending on your needs, weight, and user’s activity level. They vary in function, from basic locking knees, that remain straight when you are walking to high functioning hydraulic knees that are controlled by built in microprocessors. Your prosthetist will assist in selecting the knee that is right for you based on your needs, whether it be safety, high activity or both. Ideally you will need a knee joint that will allow the knee centre of rotation to be as close to the sound limb as possible. This is not always possible, and function often supersedes cosmetic appearance. 

Our prosthetists are experienced in using a wide range of knee joints and we are manufacturer certified to fit high end components including the X3, Genium, C-leg and Rheo XC Knee joints. 

The Prosthetic Foot

As with the prosthetic knee, the prosthetic foot chosen will be based on your weight, activity level and specific needs. There are a wide variety of feet available and options will be discussed with you in detail ensuring we match your foot to your needs. Prosthetic feet vary in their capabilities depending on the level of activity they are selected for. Some are activity specific such as running blades, they are designed specifically for running and not for day to day walking due to their energy return capabilities. They are designed for you to put a lot of weight/energy into the foot for it to release energy to propel you forward, as you can imagine, not ideal for day to day walking. The same could be said for an entry level foot, its purpose is to facilitate a smooth roll over while walking and provide a broad base of stability. Trying to run with this type of foot will lead to it failing and can cause pain or discomfort to your residual limb. 

The Look of the Prosthesis

This is determined by the shape and size of your residual limb as well as the intended use of the prosthesis. Some prosthetic users like to have the components of their prosthesis exposed, others a High Definition silicone cover to match their sound limb. The decision is yours and again this is something that needs to be discussed with your prosthesis so they can advise on what is possible and what isn’t. Setting expectations in this regard is extremely important. 

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