M.A.S. Socket
EVOLUTION OF ISCHIAL CONTAINMENT SOCKET
Marlo Ortiz Vazquez del Mercado P.O.
Ortiz Internacional S.A. de C.V.
Guadalajara, Jalisco México
Through the years there has been a transition in socket design for transfemoral amputees from the plug fitting, pre
quad, quadrilateral and the latest ischial containment.
When considering an ischial containment socket there are many socket shape variations such as: SABOLICH, UCLA,
LONG, DOMINGUEZ HILLS and prefabricated brims such as IPOS, BREAKEY and other devices.
The use of anatomical shapes are not new, in the past Thomas Canty and the U.S. Navy made some attempts to
create an anatomical A/K socket. Some techniques do not use the traditional Scarpas triangle shape and others
create an acute angle at the anterior medial corner; in our technique the Scarpas triangle shape is applied.
Our first acknowledgement of ischial containment sockets was in UCLA in 1986 and since then we have made some
modifications through the years. Some of those modifications are at the anterior aspect, we have changed it to a
quadrilateral shape; at the posterior aspect we get it closer to the posterior portion of the ischial tuberosity and we
should take into consideration the anatomical A-P and M-L dimensions
It is very important to consider the angle of the ischial ramus. The ischial tuberosity and part of the ramus as well as
the medial aspect of the ramus are encapsulated within the medial aspect of the socket brim. In the medial aspect of
the socket below the ischium the contraction of hamstring tendons over the inferior containment wall provide control to
stabilize the socket.
Although the trim lines of a conventional ischial containment socket are usually above the ischial level, the height of
the brim will depend on each individual, generally with the MAS socket the medial wall is lowered to avoid pressure on
the ramus, pressure below the ischium on the posterior wall provides good gluteal support.
In the new M A S (Marlo Anatomical Socket) design there are some differences in the trim lines. In the conventional
design posterior trim lines include part of the gluteus maximus. In the new design we have lowered the height of the
posterior wall to the gluteal fold to permit the gluteus maximus to be out of the socket. This will improve cosmesis and
there is no gluteal support. With this configuration we found that the ischial tuberosity and part of the ischial ramus are
encapsulated easily with no restriction in movement
(Fig 1A)
Not only the posterior wall trim lines but the anterior and medial walls have been lowered below the ischial level this
allows a greater range of motion and comfort. Hamstring tendons fit over the inferior containment wall to enhance a
closer fitting of the lateral wall. (Fig. 1B)
The height of these trim lines will be established according to the anatomy of each patient. From a posterior view you
can see how the cosmesis is improved and there is no gluteal support.
If we take a look at the inside shape of the new socket design let’s check the forces applied. As you are all aware
there are two main anatomical dimensions: A-P and M-L, but the resultant force is not usually considered; this force
gives us a better control of some situations such as stabilization of the lateral wall, rotational control and ischial
containment itself. (Fig 3)
(Fig.2)
The antero-lateral proximal corner of the socket is critical in order to maintain the socket control and should follow the
anatomical shape of this area for cosmesis as well.
In the anterior quad shape we have to take into consideration the measurement between the Anterior Superior Iliac
Spine and the adductor longus tendon, this give us a better idea for the anterior proximal wall dimension.
The MAS socket is not a conventional ischial containment socket design, what we have done is to move the
containment wall more anterior in order to get a medial ramus containment socket. There is no a ischial weight
bearing support and even the medial ramus is not a weight bearing area, in fact, patients should not feel any
excessive pressure over the ramus.
A maximum of ¼” (5mm) play is allowed for comfort in this area
(fig. 3)
As there is no proximal weight bearing area the design provides a quasi-hydrostatic weight bearing system over the
rest of the stump and the resultant force will provide socket control. Gluteal containment is common to other designs
but not used with the Marlo Anatomical Socket.
Dynamic Alignment
There have been many suggestions for the position of the femur. This new socket design with its very low trim lines
improves ischial containment and allows the femur to move in to an over adducted position in order to get as equal as
possible to the angle of the sound side. This will give a better functional gait.
Benefits of the M A S design
There are several benefits of this new socket design: patients can sit more comfortably, there is no plastic beneath
the gluteus, easy to put on, full range of motion, better functional gait and something very important to some patients,
cosmesis.
When donned the Prosthesis looks cosmetically very normal and its hard to find any discrepancy of the gluteus
maximus as well as any protrusion of socket trim lines. (Fig 5)
Range of motion is improved. A full range of hip flexion is obtained (Fig. 4) and depending on the length of the stump
and flexibility of the hip, patients can have a full range of external rotation where they can cross legs up to 90 degrees.
Fig. 4
Functional gait is also improved, the base gait is narrow, there is no rotation of the foot and lateral trunk bending or
lateral displacement of the center of gravity is minimized
The appearance of the hip and buttocks when patients walk is very normal and it is hard to see any discrepancy.
This socket design has been fitted with silicone liners for suspension. Some15 % of our patients have been fitted
with silicone liners and the rest with suction valve. None of them have been fitted without any suction system or
auxiliary suspension belts.
Fig. 5
