Keeping Prostheses Out Of The Closet – Socket Function, Comfort Largely Determine Prosthetic Success Level
16 Mar 2017
The prosthetic socket, essential point of integration between human tissue and replacement limb, is most often also the place where degree of prosthetic success is defined.
• It is the socket that accepts and transfers to the residual limb the stresses of weight-bearing, suspension and ambulation.
• It is the socket that encompasses and accommodates the often irregular and tender tissues of the residual limb and thereby helps determine how well, and for how long at a time, an amputee can function in the prosthesis.
• It is the socket that can, through intimate and comfortable fit, smoothly deliver the advanced gait performance promised by today’s sophisticated upper- and lower-limb prosthetic componentry.
In other words, a prosthetic limb may incorporate the most sophisticated, technologically advanced and expensive components available, but if the socket does not fit well and allow the residual limb anatomy to function to its capabilities, the result will be less than optimal, the user will not be happy, and the prosthesis may well stay in the closet.
For this reason, our prosthetic staff devotes paramount attention to designing and fabricating the best possible socket for each amputee we serve.
Sockets are as unique as the people who wear them; no two are alike, but certain principles proven to enhance comfort and functionality are built into many current-day designs:
• Total contact – Through careful creation and modification of a positive model of the residual limb, our prosthetic team forms the unique optimal socket shape for that individual. For most amputees, our goal is total contact between limb and socket.
A total contact socket enhances venous return, limits edema and reddening/ inflammation on the distal end of the anatomic limb, and helps distribute the load somewhat.
• Total surface bearing – A total surface weight-bearing socket expands on this concept by distributing forces across the entire residual limb surface. Advantages include reduced pressure on any given limb tissues, better sensory feedback to the user, improved circulation and increased proprioception.
• Reduced weight – Lightweight, high-strength sockets enable amputees to do more with less energy expenditure. One way this can be achieved is with a flexible inner socket within a laminated or rigid plastic outer frame. The outer frame covers the primary weight-bearing areas of the residual limb, while pressure-sensitive tissues and bony prominences are encompassed only by the softer inner socket.
Socket Optimization: A Challenge We Welcome Every Day
Today’s below-knee sockets are of two primary types: The “old reliable” patellar tendon-bearing (PTB) assembly focuses weight-bearing stress on certain pressure-tolerant structures, such as the patellar tendon and medial tibia flare, and relieves pressure-sensitive areas. The PTB socket is still preferred by many patients, notably those with shorter or bony residual limbs. It generally is not a good choice for patients with residual limb scar tissue and/or chronic skin breakdown.
The principal alternative transtibial assembly is a total surface-bearing socket (TSB) with a gel interface of some type (silicone or polyurethane liner, gel socks, etc.), which spreads the pressure across the entire residual limb surface at a level comfortable for the wearer.
A hydrostatic weight-bearing socket is a specific version of the TSB assembly, cast in a compression environment to achieve uniform pressure distribution across residual limb tissues. This assembly encourages tissue elongation within the liner, increasing padding at the distal residual limb and reducing potential for skin breakdown.
Contemporary above-knee designs typically employ some variety of ischial containment (I.C.) strategy, which has largely replaced the once-common quadrilateral (quad) shape. I.C. sockets feature a narrow medial-lateral dimension with the ischium encapsulated within the socket instead of sitting on the brim.
Quad sockets are still applicable for various patients, both for a preparatory prosthesis and as the socket of choice for patients who have worn a quad for many years and do not wish to change.
A particular I.C. assembly, the Marlo Anatomical Socket, originally an effort to eliminate the socket brim outline clearly visible under the clothing of female above-knee amputees, also provides increased range of hip motion and may provide added comfort for appropriate patients.
Upper-extremity prosthetic limbs are controlled by one of two primary methods: body-powered incorporating a harness and control cables, and externally (electrically) powered, typically with myoelectric control. Body-powered systems may be either harness-suspended, in which straps hold the prosthesis close to the body, or self-suspended, wherein the socket must be closely contoured to the residual limb to encompass bony anatomy or maintain suction. In either type, special care in designing and fabricating the socket is essential for maintaining control and suspension throughout the entire range of motion.
Regardless of limb or amputation level, all socket designs have benefits and drawbacks. Discerning and fabricating the best choice for any particular patient is accomplished only after thorough analysis of the individual’s physical condition and capabilities, clear understanding of his/her functional goals and careful anatomical measurements.
It’s a challenge we welcome every day.