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Fitting the Prosthesis

by Erik Schaffer, CP

A prosthetist custom designs the interface (socket and frame), then constructs it by hand. The fit of the interface, particularly the socket, is crucial to success—much more so than the type of prosthesis, including the components. If the interface fits well and is comfortable, people can function well even if the components are less than ideal. If the interface fits poorly or is uncomfortable, success is unlikely regardless of the person’s motivation or the sophistication of the components.

The socket should be designed to distribute pressure and weight bearing over specific areas. This design increases comfort, provides for the most control of the prosthesis and helps prevent the stump (skin, bones, and nerves) from being damaged. The fit should be snug, producing the appropriate amount of suction to help hold the prosthesis firmly in the socket. Movement of the stump against the socket could produce friction and damage the skin.

Traditionally, prostheses were fitted by taking a plaster mold of the stump. Now, laser scanning, using computer-assisted design and manufacturing tools, can be used. This method is more comfortable and convenient. However, whether one method produces a better prosthesis than the other is unclear. The method used may depend on the preference and training of the prosthetist.

Once the socket is fitted, the prosthetist attaches the appropriate components to the interface, to each other, or to both and aligns them so that the person can use them safely and efficiently.