Summary of responses: Expulsion valves why?...3

Summary of responses: Expulsion valves why?...3

grantxw8

7/23/2000

Probably the last reply on this subject. If anyone wants to contact the
respondent then email me and I will forward enquiries. Enjoy.

Cheers,

Grant
===================

Dear Grant,
                Been reading with interest yours and other thoughts on
air expulsion valves in TT's. Some of the responses seem to have some
understanding of the negative pressure concept, but most appear to be
practitioners with very little experience or insight into the concept.

One of the underlying principles in negative pressure fit is the dramatic
reduction in motion between residual limb and socket. When incorporating
this reduction in motion with an interface where the modulus differential
between residuum and socket is reduced, skin/liner stresses are minimized
(a critical comfort/residual limb health objective). Dr. Joan Sanders
studies (JRR&D 92-96) suggest stump/socket forces are increased by
acceleration (whether in stance or swing). She goes on to suggest the
best mode of suspension is one with little or no displacement. She
further adds the negative pressure fitting eliminates distal displacement
and most importantly skin distraction. Her research on interface
concepts is worth studying.

One further rather esoteric consideration is proprioception provided by
specific suspension modes. Proprioception is critical when the Pacinian
corpuscles in the ankle are lost (primary lower limb proprioceptors) and
amputees rely very heavily on the residuum for proprioceptive feedback
for their compensatory strategies. Negative pressure fittings appear to
enhance proprioceptive accuity. It's interesting to note that many
clients who utilize negative pressure fit comment that it feels like the
socket is directly connected to their skeleton and that they have
greatly improved fine control. This increased proprioception generally
leads to an increase in spatial awareness and confidence in the
prosthesis.

I have attached a few images of one of our patients who uses negative
pressure setups. As you will see, he presents with significant scarring
on his residuum. The patient is a butcher who is on his feet 12 hours
per day, and an A grade golfer who walks his rounds. We would not have
been able to produce a similar outcome without negative pressure fitting.
 I hate to propose subjective matter, however we have numerous similar
clients who demonstrate similar outcomes (clients with and without
heavily scared residual limbs). We've fitted in excess of 100 clients
with this mode over the last 24 months, and would be happy to share our
experiences.