Non Ischial Weight Bearing Soft Socket Design Dale A. Berry, C.P.(C) INTRODUCTION height of the ischium. This suggests that the excessive pressure and tapering of the The criteria used for fitting the above brim over major blood flow areas may be a knee socket seems somewhat ingrained contributing factor to muscle fatigue and into the prosthetic community. The ration­ distal edema problems (Figures 1 and 2). ale of socket design taught by most insti­ Moving laterally on the anterior wall, the tutes of education has been regarded as the socket expands to the rectus femorus chan­ critique and guideline for above knee nel. When reviewing the characteristics of prosthetics. This article's intent is not to the rectus femorus, it is a site of high activ­ disregard the "Berkeley" quadrilateral ity during ambulation and, more impor­ socket design as inadequate—a good tantly, the muscle changes shape and posi­ number of amputees are ambulating com­ tion during contraction. Keying the muscle fortably on limbs using its principles—yet into a channel provides an area for the a closer evaluation of the criteria appears muscle to work against, aiding in muscle warranted due to the very nature of some of fatigue and poor gait habits. The point to the socket's shape requirements. note is that as active as the muscle is, and as radical as its change in shape and position, the volume of the muscle remains constant CONSIDERATIONS at all times. The medial two-thirds of the anterior On evaluating the posterior wall design, wall is the area of the Scarpa's or femoral the basic premise of the Berkeley socket has triangle. Anatomically, the femoral artery, been "the ischial tuberosity can tolerate nerve, and vein are located in this area. It total weight bearing, therefore the ischial presents itself as a pressure sensitive area tuberosity must bear total weight." This to which as little localized pressure as pos­ one stipulation in itself tends to explain sible should be applied. On close exam­ other socket requirements and inefficien­ ination of a "Berkeley" quadrilateral cies experienced during socket fit. With the socket, bivalved through the Scarpa's tri­ ischial tuberosity posteriorly positioned, angle, it becomes apparent that the socket both the sciatic nerve and hamstring ten­ is becoming choked at a progressive rate don are bowed sharply over the posterior from the zero to four inch level below the brim. This tends to cause a slight burning Figure 2. Socket shape of Berkeley quadrilateral ischial weight bearing socket (left) and IPOS soft Figure 1. Overlay of the Berkeley ischial weight socket (right) while bivalved on a sagittal plane at the bearing quadrilateral socket and IPOS soft socket ischial tuberosity and apex of the Scarpa's triangle design. The Berkeley shape has a 3" AP, 6" ML di­ with relation to skeletal positioning. mension with a 46 cm. circumference. The IPOS soft socket design has a 46 cm. circumference with AP and ML as dictated by the casting brim. The sizing ratio of these brims have been calculated on a basis of average residual limb size, therefore, 85 to 90% of patients can be provided a secure fit without significant modifi­ cation to the brim or positive mold. The "X" indicates the preferred location of the ischial tuberosity for both sockets. sensation and leads to muscle fatigue. With ity. The highest levels of natural muscle ischial weight bearing, the necessity of activity during walking take place on the total contact along the femur to maintain anterior and posterior aspect of the brim, lateral stability and an adduction angle is yet this is the area that displays the greatest self-evident. This rationale presents itself amount of compression in a Berkeley brim. as a basic cause and effect. If the ischial To further complicate the fitting process of tuberosity wasn't positioned firmly on a a suction total contact socket, a series of pivot point (the posterior shelf) the femur reduction tables was devised in order to would not be pushed laterally to such an apply a varying degree of tension on the extreme degree. tissue. It appears somewhat inappropriate With respect to maintaining adduction to radically modify any cast taken from a angle, anatomically, the majority of hip patient; if the plaster negative fit the pa­ adductors originate in the pubic region tient well and maintained a comfortable fit, and insert in the upper half of the femur why change it? with some inserting at the trochanteric re­ Upon evaluation of the criteria for the gion. This tends to suggest that mainte­ Berkeley quadrilateral socket, it seems that nance of the proper adduction angle can be the entire casting, cast modification, and maintained at a more proximal level along fitting rationale revolve around the fact the femur. that ischial weight bearing is essential in When assessing the degree of muscle ac­ order to maintain proper socket fit and tivity at the ischial level in a Berkeley prosthetic gait. However, ischial weight socket, the levels of output can be listed: bearing may often be the cause and catalyst anterior, posterior, medial, and lateral of the majority of socket comfort and gait quadrants, in order of diminishing activ- inadequacies. Thus, an alternative socket shape seems appropriate in an attempt to • consideration for structural strength provide the amputee with a comfortable, of the socket functional prosthesis. A significant de­ • maintenance of the ischial tuberosity velopment in above knee fitting has been inside the socket the progression of the Active Shaft1 or Each wall of the socket requires specific flexible socket. The subsequent adoption demands to provide a well fitting prosthe­ of this system by the North American sis with a stable gait. The following criteria prosthetic community is rapidly increas­ will provide an excellent foundation for a ing, yet with varying levels of success. A functional flexible socket. possible explanation for this may be the fact that the outer carbon acrylic frame and flexible socket have been successfully A SOFT SOCKET DESIGN applied, but no regard appears to have This socket design, though designed for been paid to possibly the most important a flexible interface, will increase muscle factor of the flexible socket, the shape and activity and circulation, decrease muscle resultant tissue containment. fatigue, and benefit in patient comfort It is unfortunate that this critical point when used with a laminated rigid socket. appears lost in the translation of literature In addition, during early development from Europe to the United States. This stages, ischial weight bearing was inte­ factor perhaps explains difficulties experi­ grated into this socket design and found to enced in North America and not in Europe. provide superior comfort and gait over the One disadvantage of the flexible socket has Berkeley quadrilateral ischial weight been stress fractures and socket cracking, bearing socket shapes. The ischial weight an occurrence noticed here but not com­ bearing design is referred to as the "Hard monly experienced in Europe, which tends Socket Design." to suggest that socket design with radical channels and corners with excessive ten­ sion on active muscles aid in this plastic THE ANTERIOR WALL failure. Also, lateral instability is a com­ Anatomical Considerations mon occurrence, caused by ischial weight bearing, insufficient medio-lateral contact, —Adductor longus and flexible counter pressure along the fe­ —Sartorius moral shaft. This is a problem not experi­ —Rectus femoris enced with European socket design. —Tensor facia lata In developing and designing a func­ —Femoral artery tional socket shape, the residual limb and —Femoral nerve its demands were reevaluated to determine —Femoral vein the goals and considerations for a socket. —Pubic tubercle —Inguinal ligament These considerations for the socket in­ clude: Criteria • the ability to accommodate the high­ 2 • The region over the medial /3 of the an­ est degree of muscle activity possible terior wall contains the femoral triangle • allowance for easy donning and dof­ (the femoral nerve, vein, and artery). fing This area should provide uniform ten­ • no impairment of blood flow sion without excessive socket grooves or • no excessive pressure on bony land­ bulges. marks • The medial and lateral border of the fe­ • constant uniform tension on the limb moral triangle are the adductor longus • accurate casting method and sartorius muscles, both highly ac­ tive during the walking cycle. Uniform tension without restrictive socket shape 1Registered: 1976 in West Germany by IPOS KG. should be applied at these points. • The inguinal ligament borders the MEDIAL WALL proximal border of the triangle. During sitting this ligament provides a natural Anatomical Considerations crease between the anterior superior illiac spin—Pubie and s the pubic tubercle. Care should be taken to shape the brim along —Adductor longus this landmark and not to exceed proximally—Adductor magnu past sit . —Gracilis • The rectus femorus and tensor facia latae —Hamstrings tendon accommodate the lateral third of the an­ terior wall. This is perhaps the region of the highest level of muscle activity in Medial Wall Criteria regard to the muscles changing shape • This wall should be made relatively flat and position during walking. This area so as not to interfere with the sound should be uniform in shape and consis­ limb. tency without any restrictive angles or • The brim should be sloping distally from channels for the muscles to work the posterior shelf to give room for the against. pubis and to aid in function and relief for the adductor longus. • The anterior medial corner should have POSTERIOR WALL a smooth radius allowing room for the Anatomical Considerations adductus longus tendon. • The posterior medial arch should have a —Ischial tuberosity uniform radius to allow for free unin­ —Hamstring group hibited muscle activity.