There are basically three approaches used to create sockets. They were described to me by Hans Schaepper, CPO, in a presentation he made while visiting Edmonton in 2000.
The first socket is a specific weight bearing socket. This type of fitting protocol is the most common socket delivered in prosthetic clinics. It includes the patellar tendon bearing socket for the transtibial amputee and, for the transfemoral level amputee, the plug fit socket. Entertaining a socket for these types of fittings may include a polymer liner which "packs out" but will not readily tear.
The next type of socket system commonly used is a total contact socket. This type of fitting system accepts load in the more proximal area of the socket (nearest to a center or median line or to the point where the residuum originates) and prevents a uniform load distally (away from the place of origin, i.e., the end of the residuum) as relief is provided. There are liners (reference Liners for Lower Extremity Amputees in the Summer 2005 issue of AASRA News) which will tolerate being stretched and shaped without tearing; however, some of these elastomers have shown to cause skin irritation. Total contact sockets such as the quadrilateral suction socket in fact may be worn without any liner.
Total surface bearing sockets are the type of socket required with the use of urethane suction liners. They apply uniform load over the entire limb surface. In combination with elevated vacuum, this type of socket system is superior in providing comfort and control over sustained periods of time. Using this socket system, skin unaccustomed to bearing weight can stay soft and elastic without blisters or cysts.
When deciding on a liner, the prosthetist must first examine what is required of the liner to prevent the effects of forces on the residuum. Next, the prosthetist must examine the type of socket system to employ. Your prosthetist should be comfortable discussing with you the many liner choices and also be comfortable discussing the type of socket system to be employed.