Thinner, more elastic liner.

[George Boyer]

I find myself wanting to clarify how these liners enter into the
amputee's stump-in-socket situation.

My intuition tells me that the liner does cling to the skin so that
there is no relative movement there.  My suspicion also is that there is
no movement or almost none between the liner and the socket.  This means
that relative displacement is between the skin and the underlying soft
tissue, like when you grasp a pinch of skin (anywhere) between your
fingers and move it this way or that.  When you sweat the cling of the
liner to the stump skin is broken and you could tend to 'slosh' or slip
around a bit which may change the whole equation.  But skin shear is the
main enemy for comfort, aside from impingement.

Now when the distal tibia bangs up against the socket-liner combo with
the skin and all of its pain sensors in between, something happens which
causes the muscles in the uppermost extremity (head-face) to make the
mouth become round and sounds to come out eg "OUCH" :-((   This brings
to my mind a question which nothing I have ever read or heard has
addressed, namely, what are the relative durometer readings of skin and
silicone.  My feeling that the liner doesn't really cushion anything
because I think it is less yielding than the skin.  The cushioning idea
sounds nice, but I think any comfort provided comes from some other
aspect.... could be psychological (which is real)......could be from the
stump being GRASPED in this very definite way by the liner which is
indeed comfortable (an AK myself, I wear a Juzo shrinker to bed every
night for just this reason).  If the distal tibia makes any dent or
impression in the silicone liner it will do so only by giving discomfort
to the amputee.  Which means that it is necessary to provide RELIEF in
the socket wherever this may happen.  And/or insert spots of some
cushioning material which is much more yielding than the liner AND more
yielding than the skin.  The success of a talented and insightful
prosthetist in doing this and maintaining an approximation of total
contact for even distribution of weight bearing will attest to his
skill.

The variant on the silicone liners is the urethane TEC liner which may
be more forgiving of point pressures than the others but given the
relative durometers of it and the skin I can't believe that there is
very much 'equalization of pressure'.  It affords perhaps better
cushioning at eg distal tibia or other POINT problems but then goes on
to provide that all over the stump where it mostly isn't needed (with
the questionable rationale of 'equalization').

An idea I have examined for some time is that of an elastic liner of
much thinner material and shaped so as to fit the stump very closely.
(Could be thin silicone or it might be rubber, like the latex casting
sleeve of Endolite.)  Donned dry on the stump and entry into the socket
either by pull sock or a slight alcohol spray.  This would do every
positive thing that the liners now actually do, except prossibly pin
suspension, namely modify the skin shear problem and provide tissue
compression.  Would be easier to don (I have experimented) and certainly
would be cheaper (which probably is the reason the liner industry won't
be enthusiastic).

GB.


Bill Lifford wrote:

>
>
> Hello,
>
> Lately we've been discussing some aspects of the Alpha liner.  As I
> understand it, the purposes of the Alpha and other liners are as
> follows:
>
> 1.    By clinging to the skin, the residuum is protected from shear
> forces (from rotation or movement in the socket)...  nothing actually
> moves against the skin.  The shear forces are between the socket wall
> and the nylon outside of the liner.
>
> 2.    Tissue compression is achieved, which helps to "pad" some bony
> prominences and facilitate fitting.  This also makes it possible for
> total surface bearing designs to be effective.
>
> 3.     The pin systems can be used with these liners for suspension.
>
> 4.    Cushion.    The gel serves to protect bony prominences on the
> residuum.  The TEC liner is supposed to have the advantage here, as
> the flow of its urethane material equalizes pressures througout the
> limb.
>
> George spoke of the need more more sizes of these liners.  The Alpha
> is customizable using heat and a cast mold.  I don't know about the
> other types of "alpha-style" liners, such as the ICEROSS comfort, the
> ALPS, the SiloLiner, etc.    Also, the Alpha has a few different
> "internal profiles" which are supposed to work better with differently
> shaped residual limbs.
>
> One other thing:  these liners, for the most part, are designed to
> work best with "total-surface-bearing" design sockets, which are
> different from typical (traditional) PTB sockets in that the
> modifications are much "softer".  If you have a standard PTB socket
> and you add an Alpha liner, the results will be okay but not as
> effective as in a properly designed socket.
>
> Bill Lifford, CP
>
> George Boyer wrote:
>
>> Thanks for this info Esther.  However, I have the feeling that
>> fitting as closely as
>> possible would improve a person's experience & comfort with these
>> liners.  EG, would you
>> not prefer being able to avoid adding the additional piece of filler
>> which you mention?
>> As I said these items probably are optimal for those who happen to
>> fit but less so for
>> others.  Maybe additional sizing groups would help.  GB.
>
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