The AK amputee knee cannot support weight but in a limited posture, and the slightest shift of weight depending on how sensitive the knee is set up and your body posture can cause you to fall standing still even.
There are over 173,000 persons in the U.S. using a lower limb prosthesis, and between 85,000 to 114,000 new lower limb amputations each year. The prosthetic socket is but ONE of the most important part of the prosthesis for these amputees. If the socket fits well, the individual's ability to function is better but nowhere near still like a person with an able body.
If the socket fits poorly, the results are extreme discomfort, chafing, bleeding, bruising, pressure sores and pain hard to describe and which varies among amputees. These problems will reduce the amputee's functional ability, compromise their long term health, decrease independence, and increase costs to society. The traditional strategy for fabricating a transtibial amputee socket is based upon the assumption that the stump or residual limb is not uniform in its ability to tolerate load. this is NOT a true assumption.
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The "load" in needs to support is much like would be a load on the end of finger - wearing a properly fitting thimble. Uniform side pressure. Thus, the contours of the residual limb are usually subjectively modified by the prostheticist to produce a socket (i.e., rectified socket). Most research has focused on improving this socket fabrication process using complex expensive technologies (i.e., Computer Aided Design/Computer Aided Manufacture [CAD/CAM]), or determining the best modifications to produce a well fitting socket. It is all CRAP. The best fitting socket is a "plug" fit - like a thimble - with a good distal rubber or silicone pad.
This is the kind of BK technology that has been used for years - and in AK socket liners - like Alpha liners - the lower portion of the liner is thicker with the gel liner material. Let's look at it this way - if you balance the human body - all of it's weight on a single point - like say standing on one hand; you cannot maintain that for long. it will become painful and dangerous to bodily functions like circulation and bone support not made for that purpose. HOWEVER, if you way the body's weight evenly on a mattress - we all know as a bed - if done uniformly - you can get a good comfortable nights' sleep. A socket is no different. It needs to fit all around and at the bottom. Ishcial weight bearing - is largely CRAP.
One has to have a pretty boney (lacking flesh) stump to need ischial weight bearing - and it is guess what - a matter of last resort. I got an email from a prostheticist of 24 years who claimed an amputee cannot cast themselves. Again CRAP!! The guy has a financial motive to say that and two good legs to walk on. a product called Alginate is mixed and the amputee places the residual limb in the liquid. The liquid gels in about 5 minutes and the subject removes the limb. It is that simple. what you build after that is what is bit more complicated - and guess what - here is where the amputee is better and building their own leg rather than letting someone else guess at it.
Changes are on the way to the prosthetic industry. I think a lot of two legged prostheticists are going to find themselves out of work in the near future as the internet comes to those 85,000 to 114,000 new lower limb amputees each year. Stay tuned for more.