Technical Note: Light Weight Hip
Disarticulation Prosthesis
Joel J. Kempfer, C.P.
The conventional hip disarticulation prosthesis can be very troublesome to amputees
in terms of both comfort and function. Any
modifications to make It less cumbersome
and more energy efficient are greatly appreciated by patients.
By using a thermoplastic rather than laminated socket, the overall weight of the prosthesis can be reduced. Thermoplastic construction also allows for easier modification
or reliefs.
The subject of this article is a 50-year-old
male with a left hip disarticulation due to
osteosarcoma. The patient is otherwise
healthy and active.
And endoskeletal hip disarticulation prosthesis with a copolymer socket, Otto Bock
titanium components including a 7E7 hip
joint, 3R35 knee and SACH Foot was recommended.
The cast was taken using the familiar Otto
Bock technique. After the standard modifications, a polyethylene check socket was
vacuum formed using the drape molding
technique. Following successful fitting of the
check socket, a panel was cut from the check
socket and used as a shell or mounting for
joint placement (Figure 1)
. Rigid foam was
applied to this shell and shaped to accommodate the joint attachment plate. A thin stockinette was pulled over the foam, shell and
cast, and the joint attachment plate was attached to the foam using two screws. Three-sixteenth-inch copolymer (or 1/4 inch for
heavier patients) was drape molded over the
assembly, making certain that the seam ran
along the anterior midline.
After the socket had cooled and was
trimmed to the final trim lines, the foam
buildup was removed.
The plate was secured to the outer shell
with eight number 7 rivets (Figure 2)
. The
inner shell was attached to the socket with
speedie rivets, and a 1/16-inch polyethylene
tongue was similarly attached to prevent
pinching (Figure 3)
.
The finished weight of this prosthesis is
5 3/4 lbs. Reducing the overall weight by
almost 50 percent affords the amputee better
control and less energy expenditure (Figure
4)
.
In conclusion, the use of thermoplastic
technology enables prosthetists to produce
light-weight, durable prostheses. Experience has shown that this material is much
easier and less hazardous to work with compared to laminations of either polyester or
acrylic resins.
Joel J. Kempfer, C.P., is currently with Acme
Laboratories in Milwaukee, Wisconsin.
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