A Manual for Above-Knee Amputees

Ankle-Foot Systems

A variety of artificial foot designs is available, each having its advantages and disadvantages. Feet currently available can be divided into two classes: articulated -those with moving joints, and non-articulated. Those with moving joints generally require more maintenance and are slightly heavier than most of the non-articulated kind.

Articulated feet may have one or more joints. The single-axis foot (one-joint) provides for ankle action that is controlled by two rubber bumpers either of which can be changed to permit more or less motion as needed. It is often used to assist in keeping the knee stable.

A multi-axis foot is often recommended for people who have to walk on uneven surfaces because it allows some motion about all three axes of the ankle. It is, of course, slightly heavier than the other types of feet and is apt to require more maintenance as well.

The simplest type of non-articulated foot is the SACH (solid ankle-cushion heel) Foot. The keel is rigid. Ankle action is provided by the soft rubber heel which compresses under load during the early part of the stance phase of walking. The rubber heel wedges are available in three densities: soft, medium, and hard.

The SAFE (solid ankle-flexible-endoskeletal) Foot has the same action as the SACH plus the ability for the sole to conform to slightly irregular surfaces and thus makes it easier for the amputee to walk over uneven terrain. Feet of this type make walking easier because of the flexibility, and are sometimes called "flexible keel" feet.

In recent years, there has been a proliferation of new designs for artificial feet. Most are capable ofabsorbing energy in a "flexible" keel during the "roll-over" part of the stance phase of walking and springing back immediately to provide push-off, or assistance in getting the toe off of the ground, to start the swing phase of walking. Although the original idea was to provide the active athlete with more function, amputees who are a lot less active have found these designs useful. These designs are often called "dynamic response" feet.

Most of the non-articulated feet are available with toes moulded in to provide a very realistic appearance.

There are available still other ankle-foot systems that incorporate the shank and eliminate the need for a mechanical connection between the foot and shank. The shank-ankle-foot is usually made of a specially developed plastic composite that responds nicely to the forces created during the stance phase of walking.

These lightweight systems seem to have most of the advantages of more conventional designs, while providing an additional function.

Transverse Rotation Device

A transverse rotation unit allows some rotation about the long axis of the shank when it is installed in the shank between the ankle and the socket. The idea of providing this function seems to be sound, but the difficulty in designing and manufacturing a unit that is reliable has restricted its acceptance.

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Copyright 1996 - Alvin L. Muilenburg and A. Bennett Wilson, jr.

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