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July 2005 • Vol. 1, No. 2
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Advancing Orthotic and Prosthetic
Care Through Knowledge
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©2005 Otto Bock HealthCare LP
By Byron Backus, CP
During my fourteen years as a prosthetist, I have seen
many lower limb amputees who suffer from a number
of common problems, including volume fluctuation,
pistoning, skin health, and poor gait symmetry. I've also been
actively involved with the fitting of patients using well-known
solutions that have been developed over the years, including
various socket designs, pin systems, suction systems, and
elevated vacuum systems, each of which works well for
certain patient indications.
In the body of this paper, I'd like to examine each of the
physical issues in turn, and then take a look at which solutions,
based on clinical findings, research, and experience, seem to
be most effective for the amputee.
Although there are a number of common issues amputees
experience, volume fluctuation within the socket is perhaps the
most problematic because it can lead to other issues, including
decreased comfort, increased shear forces, increased
pressure on bony prominences, pistoning and skin breakdown,
as well as a poor gait pattern. Socket pressure on the soft
tissue of the limb is the main cause of this volume change.
One way to manage this change is to add socks as the day
goes on; another method is to have bladders in the socket that
can be pumped up with air or fluid as the limb loses volume
[1]. The problem with any of these methods, however, is that
the pressure in the socket will ultimately be exacerbated by the
addition of the extra material, which can cause further loss of
volume in the limb.
Volume fluctuation over the course of a day can also
cause increased pressure in certain areas because the limb can
settle further into the socket, allowing bony areas to become
more prominent and leading to more pressure, ultimately
creating more pain and possibly tissue breakdown. These
socket fit problems can also arise from other issues in the
amputee's life, such as weight gain or loss, or childhood growth.
‘Pistoning’, a situation in which the limb moves excessively
in the socket, can also occur. This can create greater shear
forces between the limb and the socket and higher peak
pressures during loading response [2]. Pistoning may be
caused by a number of different things including poor
suspension, a poorly designed socket, or volume fluctuations
of the limb.
Skin health is another prominent issue, and, if untreated, can
lead to serious problems. Constant negative pressure on the
very distal end of the limb may cause reddening of tissues and
may lead to blisters, ulcerations, and ultimately such problems
as verrucous hyperplasia [2].
Any of the above problems can add to or cause an unnatural
gait pattern, such as limping or an asymmetrical gait. This may
put unnecessary forces on the sound limb as well as the rest
of the body, and can cause overuse problems to these areas.
Various solutions in the areas of socket design and
suspension have been developed to deal with the above
problems. I'll begin with an examination of socket design. For
years, specific weight bearing sockets have been widely used
for patients with transtibial deficiencies. This design places
high loads on specific areas of the limb, and, although these
areas are usually fairly tolerant to the pressure, over time patients may suffer from reddened skin, calluses and even tissue breakdown. Researchers have studied the peak pressures
in the patellar tendon bearing socket and found that these peak
pressures can reach 300 to 400 kPa, whereas in a total contact
socket or a total surface weight bearing socket, these peak
pressures can be reduced to lower than 200 kPa [2].
A total contact socket will aid in venous return and help to
reduce the reddening on the distal end of the limb, and may
help to distribute the load of the limb a bit. A total surface
weight bearing socket takes this concept to the next level by
using the entire limb to distribute the user’s weight to the
prosthesis. The advantages to the user include less pressure
on any given area of the limb, greater circulation and
increased proprioception.
In the area of suspension systems, I would like to start with
the pin system. Originally designed as a secondary mode of
suspension, it has gained popularity in recent years as a
primary source of suspension. It is easy to don, usually
provides adequate suspension, and is easy to use. However,
during swing phase of the gait cycle, the liner tends to
squeeze the limb proximally and create a large suction distally,
possibly causing skin problems and tissue breakdown on the
distal end of the limb [2]. Higher activity will likely exacerbate
this problem, and for that reason, this type of suspension may
not be the best choice for your more active patients.
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Elevated vacuum systems drawing at least 15 inches mercury, such as the Harmony® System from Otto Bock HealthCare, maintain a consistent residual limb volume over the course of a day, improving circulation, increasing proprioception, and helping to reduce pistoning.
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Suction sockets have been around for quite some time, and a
transtibial suction socket consists of a total contact or total
surface weight bearing socket with a one-way expulsion valve
to let air out, as well as a sealing sleeve to keep external air
out. Suction sockets provide good suspension and are usually
comfortable for the patient. Very low levels of vacuum may be
achieved during swing phase with this system, but not enough
to maintain volume on the limb; therefore, one disadvantage is
that the patient may lose volume as the day goes on [1][3].
Elevated vacuum systems, which include a polyurethane liner,
a total surface weight bearing socket, and an elevated vacuum
of at least 15 inches Hg between the liner and the socket, is a
good way to manage volume fluctuations in the socket.
Instead of just pushing the air out of the socket, as with the
suction socket, the air is actively pulled out of the socket with
some type of pump mechanism such as in the Harmony®
Volume Management System, from Otto Bock HealthCare.
This elevated vacuum between the socket and the liner
maintains the volume of the limb in the socket by improving
circulation within the limb and keeping the soft tissues well
hydrated [3]. Pistoning between the limb and liner and
between the liner and socket is greatly reduced with
the elevated vacuum, and people using vacuum with their
prostheses report having greater proprioception.
Furthermore, a more symmetrical gait pattern was observed
with this type of system [1]. An elevated vacuum has also
been shown to reduce peak pressures on the limb during the
stance phase of the gait cycle and also to increase negative
pressure during swing phase. It is believed that this increased
negative pressure helps pull fluids into the limb, keeping it
hydrated and healthy [3].
Where skin health is concerned, we have seen many cases
where sores that have been unresponsive to other methods
have healed very quickly in the elevated vacuum system.
This leads me to believe that elevated vacuum encourages
good circulation in the limb. And because the volume of the
residual limb is maintained, the intimate fit between the limb
and the liner is also maintained; this prevents the sweat glands
from generating too much sweat and keeps the limb dryer in
the socket. The pump can also actively pull moisture out of the
system during activities when perspiration may be a problem.
With all of the benefits of elevated vacuum, such as volume
management, enhanced linkage, moisture management,
improved gait symmetry, and better proprioception, I think this
is a great system to have in the prosthetic tool bag, not just
for the real difficult fittings, but for many of our patients with
lower-limb deficiencies.
 Byron Backus has over 14 years experience as an ABC Certified prosthetist, and presently works in the Professional Services Department at Otto Bock HealthCare.
Board WJ, Caspers C, Street GM. A comparison of trans-tibial amputee suction and vacuum socket conditions. Prosthetics and Orthotics International. 2001; 25: 202-209). Beil T, Street G. Comparison of interface pressures with pin and suction suspension systems. Journal of Rehabilitation Research and Development. 2004; 41: 821-828. Beil T, Street G, Covey S. Interface pressure during ambulation using suction and vacuum-assisted prosthetic sockets. Journal of Rehabilitation Research and
Development. 2002; 39:693-700.
To view further studies related to this topic, please visit:
www.ottobockus.com.
Take the quiz at the Academy's Online Learning Center.
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