Ultra Lite Multiplex Mark V Modular
System Utilizing the Ultra Lite Retainer
Kit
Joseph M. Leal, C.P.
Introduction
Personal experience in fitting above-knee
(AK) amputees over a span of 30 years has
shown that one of the most difficult things to
do in prosthetics is to provide follow-up care
to a patient with a definitive prosthesis.
When trying to make changes to a prosthesis
worn by a patient, it must be recognized that
on any particular day, the prosthesis may be
fitting improperly.
It seems that we are continually faced with
this type of problem as patients both evolve
in physical condition and improve in gait.
This frustration is what inspired the concept
of a system that would allow the prosthetist
to make changes in the prosthesis as the patient evolves, the Ultra Lite Retainer Kit.
The AK Ultra Lite Retainer Kit (Figure 1)
was also designed to allow the prosthetist to
fabricate an AK prosthesis without going
through the transfer process, either in a horizontal or a vertical transfer machine. It allows the prosthetist to make any combination of angular and linear adjustments in
alignment. Alignment is recorded during the
test socket fitting procedure and subsequently utilized during fabrication of the definitive
prosthetic socket (Figure 2
& Figure 3
).
The dish that is attached to the Ultra Lite
Retainer Kit was designed so that its external
wall shape creates maximum strength in the
polypropylene thigh extension. The intent
was to provide a structurally strong thermo
plastic frame and to allow adjustments to
take place exterior of the frame. In the fabrication of the thermoplastic frame, it is recommended that 3/8 inch of stress-relieved
polypropylene should cover the entire dish
and taper up the vertical walls to the proximal end of the frame.
The development of the dish and Ultra
Lite Retainer Kit coincided with the design
of the Ultra Lite Multiplex Mark V modular
knee system. The merger of these two systems allows the prosthetist to not only make
alignment changes as the patient progresses,
but also to change knee control components
within the same knee frame.
Having a knee design that will incorporate
a variety of knee components from SNS to
pneumatics, and at the same time accommodate every marketable foot from Endolite to
Flex Foot, gives the prosthetist an enormous
amount of leeway when evaluating the patient's functional capabilities and preferences, all in the same prosthesis.
Measurement and Fabrication
One goal during measurement of the patient is to establish vertical lines on a positive
cast that determine the adduction and flexion angles and anterior-posterior and medial-lateral foot position.
Another goal is to establish the proper
knee center height, total length of the prosthesis and to calculate the distance from the
bottom of the socket to the bottom of the
socket retainer (Figure 4)
.
The final goal is to sketch the prosthesis on
a piece of tracing paper or in the mind's eye,
because once the socket retainer is fabricated, the prosthesis is essentially finished.
The alignment lines can be determined in
two ways: the first is to transfer lines made
on the patient while reclining directly to the
cast and sockets. The second is to use a
plumb bob to mark alignment lines on the
outside of the socket with the patient fitted
in the socket and standing with equal weight
on a fitting stool. Many prosthetists prefer to
use both methods in order to double-check
alignment.
To start, lay the patient down on an orthotic tracing form with hips perpendicular
to the midline and sound side heel even with
the bottom of the paper.
As shown here (Figure 4)
, the total length
from heel to ischial tuberosity or to midline
of perineum (depending on socket type) is
measurement AD.
Measure adduction and flexion position of
the residual limb and mark on tracing paper.
Place the positive model onto a vacuum
platen that will accept a mandrel. Heat the
socket material to the proper working temperature and vacuum form (Figure 5)
. Suggested socket materials are Modified Polyethylene, Thermo-Vac and Clear-Flex.
Length and Alignment
The measurement BC is the thickness of
the components from the Ultra Lite frame
knee center (Figure 6)
to the top of the socket retainer alignment wedges, where the
socket retainer will attach. For the Ultra Lite
Multiplex, this is 1 3/4 inch.
Calculate the length AB of the socket retainer to be fabricated by adding together
the total height of the structural components
(BD) and subtracting it from the total length
of the prosthetic limb (AD).
Calculate the length of plaster buildup
needed from the end of the socket to the
(inside) end of the socket retainer by adding
together the length of the socket, the thickness of the socket retainer dish (3/16 inch)
and the proposed thickness of the socket retainer at the distal end and subtracting the
result from the measurement AB.
Mathematically:
Proposed length of retainer (AB)
-minus-
Socket length
Dish thickness (3/16 inch)
Distal plastic thickness
Equals plaster buildup
The socket retainer will be built as shown
in
(Note: Socket retainer bolt and
nut will stick up beyond inside of dish approximately 7/8 inch.)
The buildup calculation is made with the
patient's residual limb or socket in the proper flexion and adduction attitude to ensure
the proper length.
Vertical alignment lines can be marked on
the patient's residual limb while on the tracing paper or later on the actual socket and
positive model, depending on the prosthetist's technique.
Fit the patient with the socket on a fitting
stool. With the residual limb in the proper
flexion and adduction, reestablish proper
height and record on the tracing paper.
Drop a plumb line along the anterior surface of the socket (Figure 2) with the residual
limb in proper adduction and mark. Adduction and M-L foot position (foot inset or
outset) is established in reference to this vertical line.
Drop a plumb line along the lateral surface
of the socket (Figure 3)
with the residual limb
in the proper flexion position and mark.
Socket flexion and A-P foot position is established in reference to this vertical line.
Fabrication of Frame
Pour the socket with plaster and place vertical alignment lines on the lateral and anterior aspects of the cast and socket. Invert the
cast and socket in the universal alignment
fixture. This fixture is infinitely adjustable in
adduction and flexion positions (Figure 8)
.
Adjust to bring the cast alignment lines to
vertical in both lateral and anterior aspects.
Attach a piece of self-adhesive Velcro to
the plastic socket to ensure that the plaster
buildup will stay on the end of the socket. Fit
a tube made of stiff paper or thin polyethylene to the end of the socket.
Orient the center point of the aluminum
dish directly over the two vertical alignment
lines in both the A-P and M-L planes (Figure
9)
. Tilt and adjust the diameter of the tube
until the end of the tube forms a circle slightly larger than the diameter of the dish. Then
attach the tube to the socket securely with
tape.
Mark the length of buildup previously calculated on a tongue blade or other disposable marker. This will act as a depth gauge
when the plaster extension is poured.
Pour plaster and modify the extension to
accept the flat inside portion of the aluminum dish (Figure 10)
while keeping the dish
centered over the cross point of the alignment lines. When the flat portion on the
inside of the dish is flush with the edges of
the plaster buildup, attach it to the extension
and blend it in with plaster. The orientation
of the slot does not matter at this point.
Prepare a 1/2-inch, 5/8-inch or 3/4-inch
piece of stress-relieved polypropylene for
vacuum forming (Figure 11)
. The plastic is
commonly clamped between two 16-inch
square frames, but the size of frame is at the
prosthetist's discretion.
Heat polypropylene in circulating or infrared oven for approximately 20 minutes or
until plastic has sagged one third to one half
the distance of the total socket and buildup
length. Although polypropylene is commonly heated at 400 degrees F, temperatures up
to 425 degrees F may be necessary to heat
the thicker sheets of polypropylene in a timely manner.
Pull the retainer slowly and evenly to obtain a uniform draw (Figure 12)
. When the
plastic seals all around the platen, apply vacuum and complete vacuum forming.
The thickness goal for the bottom of the
polypropylene retainer is 3/8 inch or more.
The demands of the amputee's activity level
will determine the proper choice of thickness.
An alternative to vacuum forming is to
apply a PVA bag to the socket and plaster
buildup and laminate a retainer using glass
and/or carbon fibers in the lay-up.
Trim and Assembly
Mark the trim lines according to socket
style. Trim the socket retainer and socket at
the proximal trim line of the socket. Drill a
hole in the distal end of the retainer through
the center slot in the aluminum dish. Use
compressed air, a wood block and a hammer
to remove the retainer (Figure 13)
. Remove
plastic socket, trim and smooth all edges on
socket and retainer to the desired trim lines.
Cut a 1 1/4-inch diameter hole in the exact
center of distal end of the socket retainer to
allow for tilt and slide when the prosthesis is
assembled.
Place the aluminum retainer dish into the
distal end of the socket retainer and attach
the socket retainer adaptor (Figure 14)
. It
will be necessary to tighten or loosen the nut
during subsequent changes in alignment and
rotation. Attach the Ultra Lite Multiplex to
the Socket Retainer Kit. Insert the socket
into the socket retainer and attach the socket
brim to the retainer with pressure sensitive
tape to prepare for final alignment.
Finishing
Plastizote or any closed cell foam is used
for cosmetic finishing of the thigh. Shape the
foam cover to the desired dimensions, allowing clearance posteriorly for the prosthesis to
flex fully (Figure 15)
.
Conclusion
As has been noted earlier, the merger of
the Ultra Lite Mark V Knee and the Ultra
Lite Retainer Kit has been of great benefit to
both the prosthetist and the patient. Allowing the patient to choose prosthetic components based on functional needs is one of the
largest benefits of this concept and design.
As we know, in AK prosthetic fabrication,
there are many changes that take place. As
amputees advance in prosthetic fitting, both
alignment and gait improve. With this improvement, it is sometimes necessary to
change components to complement the patient's new ability.
It is felt that the combination of these two
components, Ultra Lite Mark V Knee system and Ultra Lite Retainer Kit, complement the patient's ongoing prosthetic
changes. The introduction of these two components are just another tool in the field of
prosthetics to achieve total patient function.
The above article is excerpted from Technical Manual for The Ultra Lite Multiplex
Mark V Modular System, United States Manufacturing Company, 1989 and is reprinted
with permission from the United States Manufacturing Company.
Acknowledgements
The design and development of this Ultra Lite
Retainer Kit was the result of a team effort by
Joseph Leal, C.P., Scott Hornbeak, C.P.O., and
United States Manufacturing Company.
Joseph M. Leal, C.P., is a Clinical Lecturer for
the University of Arizona School of Medicine and
President of Custom Prosthetics of Arizona, Inc.,
2307 E. Broadway, Tucson, Ariz. 85719, (602)
622-0900.
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