SACH Foot with Titanium Pyramid

SACH Foot with Titanium Pyramid

SACH Foot with Titanium Pyramid

Expanding on the benefits of the traditional SACH foot, this low-activity model is created with a titanium pyramid already attached. Since no bolt is needed, this model weighs less than traditional SACH feet with a separate pyramid attachment. Available in a unisex, lifelike, water-resistant cosmesis, the SACH Foot with Titanium Pyramid offers a lightweight composite heel, flexible toe belting with three toe resistances, two heel heights, and interchangeable heel inserts. All three heel inserts are included with each foot.

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Note: Current lead time one week. Please contact customer service for delivery date.

Product Highlights:

• Low Activity (U.S. Levels 1 & 2)
• Molded-in Titanium Pyramid Makes Foot Lightweight and Inexpensive
• New Lifelike Unisex Cosmesis
• Available in Three Toe Resistances and Two Heel Heights

The SACH (Solid-Ankle Cushion-Heel) Foot

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The SACH (Solid-Ankle Cushion-Heel) Foot

Anthony Staros

Summary

On May 24, 1957, the Committee on Prosthetics Research and Development of the Prosthetics Research Board, National Academy of Sciences - National Research Council, recommended approval of the production models of the SACH Foot for adult male amputees. Plate A shows one of these newly accepted prosthetic components whose design obviates a prosthetic-ankle joint.

Concurrent with acceptance was the release of tentative manufacturing specifications as well as finalized instructions for installation and adjustment of the SACH Foot in the prosthetics shop. A pre-shaped oversize foot is now being manufactured under control of detailed specifications. Sizing and ordering criteria, final shaping, and assembly of the SACH Foot to prostheses are described in the installation and adjustment instructions which are part of this article.

Introduction

The basic functional principles of the SACH Foot are not new to prosthetic technology. Many foot designs of similar types have existed for some time. However, concerted development and evaluation performed within the Federal Government's Artificial Limb Program between 1954 and 1957 have transformed diverse predecessors into one generally acceptable and standard manufactured design. The SACH Foot for adult male amputees, although superficially simple in design, provides many of the foot and ankle functions required of prostheses. It is not a complex device, yet faulty construction, shaping, and prosthetic installation may very easily result, limiting function and causing early structural failure. Therefore, the Artificial Limb Program has recommended the release of tentative manufacturing specifications and precise installation and adjustment instructions. Adherence to the specifications by manufacturers and to the instructions by prosthetists will assure limb dealers and patients alike that the SACH Foot will always be the same valuable product that was carefully developed and evaluated in the Artificial Limb Program.

Development of the SACH Foot

In 1880, A. A. Marks patented an artificial foot designed for direct attachment to a prosthetic shank without employing an ankle joint. The patent describes using layers of rubber to provide "sufficient elasticity" for toe action, particularly at toe-off. Although not specifically claimed in the patent, the heel portion of the foot had rubber of sufficient thickness to provide some degree of plantar flexion during walking. A core made from wood, or "any other suitable material," was shaped to provide a smooth roll-over or "rocker" action at the terminus of the stance phase, similar to the SACH Foot.

In 1895, G. E. and W. L. Marks patented a similar artificial foot with an internal, inelastic core and a rubber heel portion containing a spring "free to yield with the rubber." They described the foot as having actions during heel or toe pressure that "greatly enhance the value of the foot and facilitate its use by and add comfort to the wearer."

Following these early patents, limb-shops in the United States, Germany, and Austria have used feet of designs similar to the basic SACH Foot. These designs feature an internal, rigid core or keel of proper shape and length with resilient materials provided at the heel and toe. In Canada, the SACH Foot principles facilitated designing lightweight but durable Syme's prostheses with necessary foot-ankle function.

Researchers J. Foort and C. W. Radcliffe of the Prosthetic Devices Research Project, University of California (Berkeley), developed the first prototypes of the present SACH Foot version. The development focused on selecting lightweight yet durable materials, using crepe shoe sole material to minimize weight and maximize durability. This effort defined the shape and length of the wood keel and the proper shape of the foot exterior, particularly the heel cushion made from sponge rubber laminate. Initial evaluations yielded extremely favorable amputee reactions, particularly to the heel's shock absorption and the smooth transition of weight from heel to toe during the stance phase.

Advantages of the SACH Foot

The absence of mechanical articulation in the prosthetic foot-ankle region eliminates maintenance problems due to frictional wear, such as noises, joint looseness, instability, and inconsistent function. Design and construction defects of conventional foot's rubber bumpers have often resulted in repeated limb-shop maintenance and patient inconvenience. The direct assembly of the SACH Foot to the prosthetic shank overcomes these difficulties while furnishing necessary prosthetic foot-ankle function.

The heel cushion provides shock absorption at heel contact, equivalent to the plantar flexion of a conventional ankle. As the amputee walks, the foot simulates ankle dorsiflexion, providing smooth roll-over or "rocker" action just before push-off. The location of the "toe-break" or roll-over line is closer to the prosthetic shank’s vertical center line, reducing energy consumption during walking, particularly up inclines.

Specifications of the SACH Foot

Tentative specifications cover the SACH Foot's manufacture, requiring feet to be pre-shaped oversize by a manufacturer. The SACH Foot must be carefully fitted to the amputee's shoe to avoid adverse function limitations imposed by the shoe. The manufacturing specifications detail heel cushion compression properties and product dimensions, with tests performed as checks for structural and functional characteristics. Installation and adjustment instructions will be provided to prosthetists to ensure proper fitting and function.

Functional Characteristics

The SACH Foot provides shock absorption and ankle action characteristics equivalent to a normal ankle without an articulated ankle joint. This action is achieved by a wedge of cushioning material built into the heel and an internal structural core or keel shaped for a rocker action. The cushion heel simulates normal plantar flexion efficiently, allowing for smooth action without the sudden changes in resistance typical of conventional feet with articulated ankle joints.

Sizing and Ordering Specifications

SACH Feet are available in rough-shaped oversize blanks in three shoe-size ranges: 6-8, 8-10, and 10-12. Each size range shares a common keel size, with specific toe-break to ankle distance. The heel cushions come in three stiffnesses: soft, medium, and hard. The medium heel cushion is suitable for most applications, but if necessary, other stiffness types should be ordered based on trial or experience.

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When ordering foot blanks, specify: (1) Size range; (2) Right or Left; (3) Heel Stiffness Desired; e.g., 8-10 R Medium.

Shaping

Do not shape the ankle portion above the shoe level until the foot is finally installed on the shank with proper toe out. Leave the ankle area rough-shaped for walking trials. Proper shaping is crucial for function and appearance. The heel cushion, upper and lower arch surfaces, and toe section require particular attention. The general contours necessary for functional shaping are pre-shaped into the oversize foot blank. Only minor changes in contour are required.

When fitting the foot into the shoe, always use a thin sock. Shape the heel to fit the shoe tightly near the sole but with considerable clearance near the heel counter's brim. This clearance allows the heel cushion to expand without interference, preventing hose wear. Shape the bottom arch surface to provide a minimum of 1/8" clearance between the foot and the shoe’s inner sole to avoid restricting motion and causing shoe damage.

Installation

The SACH Foot is attached to a conventional wooden shank with a 3/8" steel carriage bolt. During manufacture, the carriage bolt is inverted and its head is embedded into the hardwood keel's lower surface. A solid section of wood in the shank's end is required for installation. An allowance for extra shank length, typically 1/4", is necessary to compensate for the foot's compression under load. After toe-out adjustment and walking trials, the foot is glued in position. Use "Woodlock" or similar water-resistant adhesive for gluing and doweling the foot to the shank for maximum security.

Adjustments

The SACH Foot allows adjustments in heel cushion stiffness and thickness. Adjust heel elevation if there is excessive heel cushion compression or insufficient compression in the standing position. To increase heel elevation, sand foam crepe sole material from the heel bottom. To decrease heel elevation, cement shims of crepe sole material or leather to the heel area’s bottom. Exchange the heel cushion if proper adjustment does not resolve installation issues.

The prosthetics ankle manufacturers offer comprehensive guidelines and support for installing and adjusting the SACH Foot for optimal performance.

References:

1. Marks, A. A., Artificial Feet, Patent No. 234,596 (November 16, 1880), U.S. Patent Office.
2. Marks, G. E. and Marks, W. L., Artificial Foot, Patent No. 546,405 (September 17, 1895), U.S. Patent Office.
3. New York University, College of Engineering, Research Division, Prosthetic Devices Study, Evaluation of the Solid Ankle Cushion Heel Foot, Report prepared under Veterans Administration Contract V1001 M184, June, 1955.
4. New York University, College of Engineering, Research Division, Prosthetic Devices Study, Evaluation of the Solid Ankle Cushion Heel Foot (SACH Foot), Report prepared under Veterans Administration Contract V1001 M184, May, 1957.
5. Prosthetics Research Board, Committee on Prosthetics Research and Development, Minutes of Conference, June 16, 1956.
6. Prosthetics Research Board, Committee on Prosthetics Research and Development, Minutes of Conference, May 24, 1957 (Unpublished).
7. University of California (Berkeley), College of Engineering, Prosthetic Devices Research Project. Fundamental Studies of Human Locomotion and Other Information Relating to Design of Artificial Limbs. Vols. I and II, Reports prepared under Veterans Administration Contract VAm-21223, 1947.
8. Veterans Administration Prosthetics Center, Testing and Development Laboratory, Tentative Standard for Foot, Solid Ankle, Keel Type, Elastomer Heel Cushion for Lower Extremity Prosthesis, May 15, 1957 (Unpublished).