Prosthetic Socks
Traditionally, prosthetic socks have provided
cushioning and a means to adjust the volume
of the socket. Prosthetic socks are available
in several materials including wool, cotton and
synthetics. Sock thickness is measured by the
“ply” rating, most commonly from 1-ply to 6-ply.
By varying the ply number and/or the number of
socks worn, amputees can adjust for changes in
the size of their residual limb. Prosthetic socks
should protect the skin against the destructive
forces of pressure and friction in the skin-socket
interface, while also absorbing perspiration with
a wick-like action and allowing for ventilation.
Sock Materials
Wool
Wool is an excellent fiber for prosthetic
socks due to its resiliency, absorbency and
conformability. Wool’s resiliency offers
cushioning and provides maximum comfort
to the wearer. Its ability to absorb perspiration
quickly without feeling wet provides excellent
comfort in cold, hot, humid and dry climates.
Due to the variety of residual limb shapes, it is
also important for the prosthetic sock to conform
to the contours of the limb without wrinkling.
Knitted wool provides a smooth, wrinkle-free fit.
Cotton
Cotton has limited application as an interface
material in prosthetics. Its advantages are that
it is nonallergenic and neutral to any skin type.
It can also be washed and bleached with little
dimensional change and it is tough; however,
cotton does not offer the level of absorbency or
the cushioning provided by wool.
Synthetic Fibers
Man-made fibers are widely used in the
production of prosthetic socks and may be used
alone in their construction or in combination with
natural fibers. One example of an all-synthetic
sock is made of polypropylene and Lycra. This
combination provides wicking of perspiration and
transports moisture across the fiber and away
from the skin. The Lycra serves to accommodate
edema or atrophy more easily due to its elasticity
and ability to return to its prestretched shape.
Wool is increasingly being blended or
combined with man-made fibers. These products
provide the softness, strength or resiliency of the
man-made fibers used and are easier to care for
because they tend to resist shrinking and felting.
They also cost less than all-wool socks and can
take advantage of plaiting - the knitting of one
fiber on the outside of a sock and another fiber
on the inside to benefit from the qualities of both
fibers. One such sock uses wool on
the outside for resiliency and toughness
and Dupont CoolMax on the inside,
which provides softness and keeps the
skin cool by transporting perspiration
away from the skin faster than any other
fiber. The fibers spread perspiration over
a larger area so that it will evaporate
more quickly. This sock also contains
Microsafe fiber that resists bacteria
and fungus growth for skin health and
odor reduction. Lycra/spandex provides
excellent conformability and free motion
of the knee.
Nylon sheaths come in white and flesh.
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Flesh-colored nylon sheath with silicone insert.
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Different ply of prosthetic socks: Top: 5-ply Middle: 3-ply Bottom: 1-ply
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A typical 5-ply prosthetic sock.
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Nylon Sheaths
Nylon sheaths perform the valuable
function of providing a moisture barrier
and controlling friction between the skin,
the sock and the prosthesis. Sheaths
look like hosiery but are specially
constructed at the distal end to offer
maximum smoothness. The top and
toe are reinforced so that pulling taut
is possible; however, leaving a little
slack is advised to prevent stressing
the sheath. Sheaths are generally worn
in combination with a thicker sock,
creating a prosthetic sock system.
Gel Socks
Socks and sheaths are also available
with gel attached to, or sandwiched
between, the fabrics. The gel is usually
made of silicone and provides excellent
cushioning, pressure distribution
and reduced friction. The thickness
and stiffness of the gel will dictate
the cushioning qualities of the sock.
Because gel tends to flow from areas
of high pressure to areas of lower
pressure within the socket, maintenance
of a more even pressure distribution
is possible. If the sock or sheath is
constructed with the gel exposed,
the gel should be worn against the
skin. This will help protect the skin
from the friction forces created during
walking, since the motion will tend to
occur between the gel sheath and the
prosthesis rather than between the gel
and the skin.
Volume Management
All amputees are aware that the size of
their residual limb changes over time.
Most experience subtle, and sometimes
not so subtle, changes in volume over
the course of a single day. Factors that
affect the volume of the limb include
reduction of postoperative edema,
muscle atrophy, changes in body weight
and the temporary reduction of fluids in
the limb caused by the normal pumping
action of walking in a prosthesis. To
maintain an even, comfortable fit, it is
necessary to accommodate for these
volume changes by adjusting the
thickness of the prosthetic socks. This
can be done either by changing to a
thicker sock, i.e., from a 3-ply to a 5-ply,
or by adding another 1- or 2-ply sock
over the existing sock. Care must be
taken not to overdo this. If too many
socks are used, the socket will not fit
properly and may cause discomfort and
skin breakdown.
Liners
For purposes of this article, I will limit
my discussion of liners to those that
are worn directly against the skin and
either take the place of socks or are
worn in combination with them. Over
the last decade, we have witnessed
a rapid increase in the variety of liners
commercially available. Depending
on their intended use, these liners
can offer some or all of the following
benefits: excellent protection against
friction, dynamic pressure distribution
resulting from the “flow” characteristics
of the materials, and suspension of
the prosthesis when fitted with a distal
attachment.
Liner Materials
Prosthetic liners are available in silicone,
urethane or a mineral-oil derivative. They
are applied by turning the liner inside
out and then pressing the closed end
against the residual limb and rolling the
liner onto the leg. They are available with
or without a fabric backing, which can
ease donning of the liner as it allows
the material to easily slide against itself.
The backing also serves to reinforce the
gel for improved durability. All of these
liners are airtight so that perspiration
cannot escape. This is generally not a
problem, however, because the skin
tends to sweat less within the airtight
liner once it is accustomed to the sealed
environment.
Locking Liners
Silicone Suction Sockets were first
introduced in the mid-1980s. These
liners are made of a relatively thin
silicone and their primary purpose
is suspension of the prosthesis. An
attachment mounted on the end of
the liner mates with a locking device
on the end of the prosthetic socket,
thereby providing a secure coupling of
the residual limb and the prosthesis.
These liners also protect the skin against
shear forces because movement occurs
between the outside of the liner and
the adjacent material. Later, thicker
liners were developed with a softer
gel that provides more even pressure
distribution as the gel material flows
from areas of high pressure to areas
of lower pressure. Today, these liners
are available with or without the distal
locking feature and are usually worn
with traditional prosthetic socks to allow
for volume adjustments.
Oils and lotions such as mineral oil
and Aloe Vera may be integrated within
the gel liner to help prevent drying and
chafing of the skin.
Hygiene and Sock Care
Prosthetic socks and liners should be
washed daily, carefully following the
manufacturer’s recommendations.
Wearing a sock stretches it and
perspiration hardens it. Washing and
proper care restore its shape and soften
it. Proper care of socks will reward
the amputee with longer service and
greater comfort. A sufficient supply of
socks should be maintained to allow
clean socks to be worn each day and to
allow several days after washing before
wearing. Wool socks should be worn
in rotation, as this gives an interval of
several days during which the socks
can “rest.” Such a rest period allows
the wool fibers to regain their natural
resiliency and elasticity for optimal
comfort.
Conclusion
Socks and liners are a critical
component of the prosthetic system
and impact comfort dramatically.
When used properly they provide a
cushioning effect within the socket, help
to minimize friction forces, and provide
even pressure distribution. As with other
prosthetic options, the selection of the
most appropriate socks and/or liners for
each amputee depends on a variety of
factors that are best explored with his or
her prosthetist.
—by Jack E. Uellendahl, CPO
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