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A New Concept in Above-Knee Socket Design
By Al Pike, CP
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Figure 1 |
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During the 1940s and 1950s, the most common type
of socket for the above-knee amputee in the United States was an
ischial containment socket (ischial tuberosity within the walls of
the socket) called a "plug fit" or "anatomical" socket. The
suspension method used for these prostheses was suspenders, pelvic
belt and band, or air chamber suction.
By the 1960s, the schools of prosthetics at New York University,
Northwestern University, and the University of California were
teaching the quadrilateral socket shape. During the 1980s, Ivan
Long, CP, introduced us to Long's Line, and not long after that,
John Sabolich, CPO, described the Contoured Anterior Trochanteric
Controlled Alignment (CAT/CAM) Method.
During these years the "ischial containment" socket has gone
through a number of changes.
Ortiz Design: Major Improvement
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Figure 2 |
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In the field of socket designs, Ing. Marlo Ortiz
Vazquez del Mercado of Ortiz Internacional, S.A. de C.V., Mexico,
has developed what may be a major improvement on the ischial
containment concept.
Like many innovations in prosthetics, this new development began
with an amputee requesting something better. It started in 1999
with prosthetist Marlo Ortiz trimming down the posterior wall of an
ischial containment socket to make it more cosmetic in the gluteal
area. What evolved is a socket configuration now called the
MASdesign (Marlo Anatomical Socket). Más is also Spanish for
more.
Like others before him Marlo Ortiz is sharing the findings of
his work with other prosthetists, in hopes of benefiting more
above-knee amputees. He first presented his design at the Spanish O
& P Federation Congress in Seville, Spain in October, 2000.
Other presentations followed in the United Kingdom and the United
States, including at the annual meeting of the Amputee Coalition of
America (ACA).
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Figure 3 |
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Señor Ortiz found that it was possible to
lower the posterior shelf, and in doing so realized the
ischial/ramus area was easier to contain when there was no
interference from the gluteus maximus (Fig.1). These changes also
contributed to the greatest range of motion when wearing an
above-knee prosthesis (Fig 2).
Overall trim lines are lower than the ischial tuberosity, with
the exception being the medial aspect of the ramus and the lateral
wall, depending upon the anatomy of the amputee (Figure 3).
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Figure 4 |
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With the gluteal cutout, no weight-bearing occurs
in this area, and weight-bearing forces are vectored from the
captured medial aspect of the ramus with a resultant force
projecting to the anterior/lateral area of the socket. Fig. 4 shows
an overlay of the MASdesign over a typical ischial containment
socket.
It was found that lowering the height of the posterior wall
enabled easier encapsulation of the ischial tuberosity and part of
the ramus. With no restrictions or interference from the
hamstrings, closer fitting of the lateral wall was obtained.
However, an exact fit is critical to the success of the socket.
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Figure 5 |
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In Fig. 5, we see the cosmesis that can be
obtained, and in Fig. 6, the added mobility the amputee can display
without the use of a mechanical rotation device. Sitting comfort
for the amputee wearing an ischial containment socket is improved,
and donning of the socket is easier.
Videotapes have shown that the above-knee amputee has better
control of the prosthesis and a more functional gait.
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Figure 6 |
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M.A.S. Socket: A Transfemoral Revolution
- June 2004
The M.A.S.® socket design is an evolution—and perhaps even a “revolution”—in the development of ischial containment (IC) socket concepts.
Cutting Edge
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Table Of Contents - November 2002
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