A limb prosthesis has three main parts: the interface, the components, and the cover.
Interface: The prosthesis attaches to the body at the interface. The interface consists of a socket and a rigid frame. The socket, which is made of plastic or laminated material, is where the working parts of the prosthesis (the components) attach to the person. The frame, which is made of graphite or similar materials, provides structural support for the socket.
A liner is worn between the remaining part of the limb (stump) and the socket to provide cushioning and to make the fit tight. The liner is made of soft polyurethane or silicone, which clings to the skin without causing friction. Ideally, people should have two liners for each prosthesis. Alternating the liners from day to day can make them last longer. They maintain their elasticity and shape better when they are not worn on consecutive days.
A prosthetic sock may be worn instead of or with a liner. 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). By putting on several socks or socks of different thicknesses or by taking socks off, a person can make the prosthesis fit better as the stump changes size, as it does normally throughout the day when activities, weather, and other factors change.
The interface may include devices that help hold the prosthesis on securely (called a suspension system). The following suspension systems are commonly used:
Suction valve: When the stump is put in the socket, air is forced out through an opening at the bottom of the socket. A one-way suction valve on the socket closes the opening and forms a seal that holds the prosthesis in place.
Liners with a locking pin: Most liners are locked into the bottom of the socket by a notched pin. Because the pin is pressed tightly against the stump, the parts of the stump near it can become irritated and inflamed, fluid may accumulate, and skin sores may develop.
Belts and harnesses: Sometimes the prosthesis is attached by a belt or harness. These devices may be used by people who have difficulty keeping the prosthesis on with a suction valve or locking pin or who cannot tolerate the pin. However, the harness is relatively rigid and thus can be uncomfortable and cumbersome. It may also restrict movement.