A Manual for Above-Knee Amputees

Above-Knee Prosthesis Fabrication

Whether the prosthesis is to be a crustacean or an endoskeletal (often called "modular") type, the prosthetist begins by wrapping the stump with plaster-of-Paris bandages to obtain a negative mold. A positive model is made by filling the negative mold with a mixture of plaster-of-Paris and water, and allowing it to harden.

After modification of the model to provide the proper characteristics in the finished socket, a plastic socket is formed over it. The first socket is usually transparent for use as "test" or "check" socket to determine if further modifications are needed.

A new method being used by some prosthetists for obtaining a modified model of the stump involves use of a computer and automatic machinery.

Known as CAD/CAM, (Computer-Aided Design \ Computer-Aided Manufacturing), this system permits prosthetists to modify the model more easily since it does not require making and carving an actual plaster model.

The socket is mounted on an adjustable leg for walking trials, and when both the prosthetist and the amputee are satisfied, the limb is ready for the finishing procedures. The crustacean shank may be of plastic-covered wood or all plastic. The endoskeletal type uses carved foam rubber over the supporting tube and the entire prosthesis is encased in a latex or fabric stocking.

Steps in the fabrication of a plastic prosthesis for the trans-femoral amputee are:

  1. A negative mold of the stump is made by wrapping it with a wetted plaster-of-Paris bandages.
  2. The cast is filled with a mixture of plaster of Paris and water to make a positive model.
  3. After modifications have been made to the positive model to make sure that the pressure on the stump will be distributed properly, a check, or test, socket is made by forming a heated sheet of a clear plastic over the modified model.
  4. The clear plastic socket is tried on to make sure that it fits properly.
  5. A new positive model is made by filling the clear test socket with a mixture of plaster of Paris and water.
  6. The socket to be used on the definitive prosthesis is formed over the model either by using a mixture of plastic resin and cloth or by forming a heated sheet of plastic over the model.
  7. &
  8. The definitive socket is attached to an adjustable leg for alignment and walking trials.
  9. The finished prosthesis may be either the crustacean or the endoskeleton type.

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

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