Socket design deals with the interface between carbon fiber/titanium, and the soft squishy parts. It is nowhere near as interesting to me as the bio-mechanical or electronic knees.
While socket design and building, is the less "sexy" part of prosthetic wear, it has the distinction of being the most important.
A comfortable, pain free socket will be worn all day.
An uncomfortable or painful socket will get little use.
I would more likely wear a good socket with a broomstick on the bottom, than I would wear a million Rand bionic leg that fit poorly.
A well designed bionic knee may be used by thousands of people, but because every stump is different, every socket must also be different. A prosthetic knee is science and technology. Designing and building a good prosthetic socket, is art.
For trans femur amputations, the shorter the femur, the less stump to attach a socket to. Every inch shorter the femur is cut, means almost 10% more energy required to walk on a prosthesis. That is one reason the Paralympics classification system can not ever work. Every stump is a different length.
All the top T-42 athletes (Amputation above the knee) are knee dis-articulation amputees. In a knee dis-articulation, the leg is amputated between the femur, and the shin bones. No thigh muscles are cut, and the femur remains intact. This also allows the full body weight to be applied to the end of the femur.
Before my amputation surgery, the Doctor and I discussed whether it would be necessary to cut my femur. It turned out I had a suspicious growth just above and behind the knee. It was decided to cut the whole suspicious section away, and that include about 1.5 inches of femur. This left me with a shortened femur, but a relative long, shortened femur. That extra length means more leverage in stump movement, and more area to attach a socket on to.
There are basically three different socket design theories. Most sockets are a combination of all three designs:
1. Plug socket. This is what the peg leg pirates wore. Basically a cup that the stump fits into. Most of the body weight is supported not on the end of the stump, but on the fat around the top of the thigh. My last adjustable, socket with all the holes was like this. Usually plug sockets are held on to the stump with belts and straps.
2. Ischial containment socket. When you sit for a long time on a hard surface, (like stadium bleachers) discomfort comes from the pelvis bone pushing on the skin and muscles against the bench. This part of the pelvis that you sit on, is called the Ischial bone. An Ischial containment socket makes a small cup like platform on the top of the socket, that cups the Ischial bone. So while standing or walking, the body weight is on the Ischial bone, and not on the stump. These sockets are held on with suction between the end of the stump, and the socket. My old Texas flag socket was like this. It tried to keep all the weight off the stump, and put it onto the Ischial bone. As you can imagine, walking with the Ischial bone cupped, is not pleasant. Another uncomfortable thing with Ischial sockets is sitting down, because of the Ischial lip pushing into the thigh.
3. Quadrilateral socket. This type of socket is sort of a square shape instead of being shaped like an oval. It tries to control and contain the movement of the femur within the stump. It puts much of the body weight on the skin and muscles of the stump. By me adding lots of thick foam pads in my last adjustable socket, I was turning a plug socket into a quadrilateral socket. These sockets are held on with suction, or vacuum.
Here is a picture comparing the Ischial socket, with the quadrilateral socket. Both are for a left stump, and the front of the stump is to the right of the picture.
Most modern sockets are a combination of all three types of socket designs.
Yesterday I spent a few hours at the prosthesis place. We looked at and talked about all my foam insertions in the socket that I wore over the weekend. I wore the prosthetic leg about 6 hours on Saturday, and 12 hours on Sunday. Being able to adjust the tightness was welcome when wearing it for long periods of time.
I felt more like I was wearing a crutch that fit on my stump, more than a walking prosthesis. The farthest I walked was to the mailbox, about 10 Meters. It caused no pain, but was very uncomfortable. If it was my permanent prosthesis, it would live in the closet, not on my stump.
Yesterday Bradley took another cast impression of my stump. He wants to build a quadrilateral-ish style socket. One that tightly controls my femur. Holding it in place and immobile. My femur tends to move in an outward, (Doctors call this Abduction) sideways direction when I put weight on the stump. The movement, while not painful will result in pain after a few hundred steps.
The previous sockets that I was able to do the 5km runs in, also strongly controlled the femur, but as my stump shrunk in length, the femur was forced into the stump end, and this soon made that type of socket painful, and hurt me inside the stump end. This put me in a wheelchair for a few months.
Then we tried the Ischial containment, which helped to reduce the pain from the socket on the stump end, but was very uncomfortable.
Today I go to Bradley again to try a new socket. This one will be more of a quadrilateral design. It will tightly control the femur, and at the same time not allow the femur to press against the stump end, by supporting my weight with use of a small Ischial cup, and the fat around the top of my thigh.
I guess you could say, that this socket I'll try today is 10% Ischial, 30% Plug, and 60% Quadrilateral. It will be held on with suction.
I will have to wear a different silicone liner. This one has a soft ridge around it to seal in the suction. This liner is thinner and larger than my other one. Much easier to put on. :-)
This may look a tad phallic, if your weird. :-)
Many people confuse "suction" with "vacuum".
Suction is caused by trying to remove something, from within something, without any way for air to get inside to replace what is being removed. Vacuum is when you actively remove the air from a container.
My sockets so far have been suction. As I push the stump down into the socket, the air is squished out. The design of the liner prevents any air from getting back into the socket, so a suction is formed between the end of the stump and the socket. There is a small valve at the bottom of the socket for the release of suction and allows air back into the socket. Otherwise I could never get the socket off.
Some very expensive, modern sockets are held on with vacuum, not suction. There is a small air pump that sucks air out of the socket. This "elevated vacuum" makes the entire stump swell to the exact shape of the socket. It gives a very firm and perfect fit between the stump and the socket.
There is so much R&D needed for medical equipment, and so few actual sales, that prices for all prosthetic hardware is very high. For me to buy an elevated vacuum system, I would first need to sell my house.
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18:00
I am just back from Bradley's. My new socket feels great so far.
You can see the lip for the Ischial bone. It is about a 30% Ischial, 30% Plug, and 40% Quadrilateral.
The Ischial seat is great for standing, but rubs a bit while walking. My stump goes quite far down into the socket, but the Ischial lip stops any further going in.
I'll try it for a few weeks, then go back for a fitting. I am sure that wearing it lots will force the stump to shrink even more.
For the first time in many months, I am thinking about going to the USA I think if I had a good prosthesis that could be worn all the time, then getting around inside the RV would not be to hard. Showering would be just about impossible. I will need to do a sponge bath.
I can't wait for tomorrow when I can play with the new socket a bit.
I am excited.....
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I'm so glad about your new socket. I hope that your trip to the States will become a reality soon.
ReplyDeleteExciting!
ReplyDelete