A New Concept in Above-Knee Socket Design
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
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).
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).
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.
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.