Saturday, April 1, 2023

“O” Ring AK Total Suction/”O”Ring AK Total Suction-Pin Suspension

Dear Colleagues:

Several of you have written to me asking for more details about the

“O” Ring, AK Total Suction/ “O”Ring, AK Total Suction-Pin Suspension.

I am hoping this idea and others will contribute to solving the problem of

maintaining suction and suspension in AK/Trans Femoral sockets.

The principle is to provide a proximal “O” ring seal (which is a

circumferential thickening)

that is created just distal to the medial border.

I have done this with success in both total suction socket (wet fit) and in

Pin suspension sockets where an airtight shuttle lock is employed.

The reason for using it with a pin suspension system is to give the advantage

of both total suction and pin suspension. Either system allows for socks to

compensate, but they must be placed distally to the “O” ring seal so they

don’t interfere and cause the suction to be lost.

This idea has been suggested before with the FlexSeal. In principle the Flex

seal sounds good, but it requires special fabrication, the part is somewhat

fragile, and I personally have not been able to find anyone that has good

results with it. Perhaps the idea just needs some reworking. For details you

might contact the manufacturer.

TEC-(Carl Caspers) has , at least in the past, recommended a compressive ring

built into the socket at a proximal level to be used in conjunction with his

TEC liners in AK candidates.

I think its important to remember that we are looking for a seal, and not so

much compression that might “choke” the residuum.

What I have tried is placing 3 to 6 cm strip of PVC coated PeLite (vinyl

coated PeLite distributed by Fillauer, Knit Rite and probably others) around

the inside of the socket

about 1 to 2 cm below the proximal brim. I skive the proximal and distal

longitudinal edges as well as where they overlap for smooth transitions.

Sometimes I have used sticky backed lycra at the point the strip meets ,

again for a smooth transition.

While I have suggested using sticky backed foam window insulation that would

then be covered by a piece of vinyl or perhaps sticky backed Lycra material,

I have not tried this yet. I like the idea of a compressible material such as

a foam or gel material. I believe the vinyl coated Pelite works well with gel

liners and fleshy residuum’s where there is possibility of “choking”

In addition, I have a client/pt now who is wearing an Alpha liner pin

suspension with an Alpha lock. He currently has total suction (the socket is

new) but he has volunteered to try another idea to maintain suction.

Rather than use an external “O” ring, I am considering trying a 2-3 cm wide

piece of a 6 mm Comfort liner or ALPS EZ liner. This comes from the discarded

piece of a liner that was trimmed for length. I cut a piece of the liner so

that I essentially have a large rubber band. I remove the cloth backing so

that it stretches easily. I will then have the amputee put the ring of

silicone on their thigh and then don the liner over it. The silicone ring

should be as high as possible but still covered by the liner and of course

distal to the medial border of the socket. While I haven’t tried this yet, it

relies on the competency of the amputee to don it properly. The soft

durometer of the gel sounds appealing for achieving a good seal and a

comfortable seal.

The pin suspension liners I use have a fabric coating. This has not presented

a problem in maintaining suction external to the liner. However, if it did,

smearing a circumferential silicone band in the same area as the “O” ring

would probably solve that problem.

This idea should be able to be used with a lanyard system as well, if the

lanyard has an airtight seal.

While it has been suggested that using a thicker liner is also a solution

when suction has been lost between the liner and the hard socket, the

distribution of gel in the thicker liners is not uniform.

This may or may not present a problem, but it does add expense. And the

question in my mind is, do I use the thicker gel medially to keep from losing

ischial containment, or perhaps laterally as some would say to protect the

distal femur or , for that matter, anterior or posterior? Maybe its

inconsequential but I don’t have experience with this yet.

Perhaps pre-skived vinyl covered PeLite or other suitable “O” ring type

material will become available, or even a gel like material with covering and

sticky backed.

In countries where these materials are not available, skived leather over

PeLite or other material might provide the same effect for total suction

sockets. If socks are available to put on distal to the “O” ring , it allows

the wearer to adjust his own socket.

Mark Benveniste CP


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