special subjects
Prosthetic Components
Interface between the residual limb and prosthesis
The prosthesis attaches to the body by direct skin contact or by an interface made of various thin viscoelastic cushion materials worn over the residual limb. Agel cushion interfaceis worn over the residual limb (stump) to provide skin protection and modulate and more evenly distribute pressure. Custom molded interfaces may be necessary to accommodate irregular stump contours (eg, deep scars, sharp bones, burns). Ideally, patients should have 2 identical interfaces for each prosthesis so they can be alternated day to day, which helps them maintain their elasticity and shape and last longer. Interfaces are typically recommended to be replaced every 6 months and, for very active patients, every 4 months. Aprosthetic sockmay be worn instead of or with a gel interface. Socks are made of wool, nylon, or synthetic fabrics, sometimes with gel sandwiched between the layers of fabric. Socks are available in different thicknesses (plies). Prosthetic socks are used to manage volume changes during the day as a result of muscle atrophy, weather, or activities. When the patient cannot maintain a comfortable, stable fit with the use of volume-management socks, the prosthetist will make socket adjustments according to volume measurements and muscle shape changes. Anintegrated suspension system, which may be part of the cushion interface, is used to help hold the prosthesis on securely. The following suspension systems are commonly used: Vacuum:An electric or mechanical vacuum pump removes air from the socket. This is the most effective method for holding a prosthesis to the residual limb and also provides greater fluid volume stabilization in the residual limb. Suction:When the residual limb is put in the socket, air is forced out through a one-way expulsion valve at the bottom of the socket, which results in suction that holds the prosthesis in place. Interface with a locking pin:A cushion interface with an integrated suspension pin at the bottom is inserted into a locking mechanism embedded in the bottom of the plastic socket. A release button disengages the pin for removing the prosthesis. Belts and straps:Sometimes the prosthesis is attached by a belt and/or straps if keeping the prosthesis on with vacuum, suction, or pin is difficult or cannot be tolerated. 