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These three aspects of prosthetic rehabilitation represent the critical design features of a prosthesis. Each aspect is important in it's own right and can be considered individually yet all three aspects are interrelated. Comfort is arguably the most important of these features for without comfort, function and dynamic appearance become unattainable.
If a room full of amputees were asked what the most important feature of their prosthesis is, certainly comfort would be high on the list of responses. Without comfort, the most technologically sophisticated components become useless. At the most basic level, comfort within a prosthetic socket is achieved by good pressure distribution and the management of friction (shear) forces.
Over the last decade, there has been a rapid increase in the variety of liners commercially available. Depending on their intended use, these liners can offer some or all of the following benefits: excellent protection against friction, dynamic pressure distribution resulting from the "flow" characteristics of the materials, and suspension of the prosthesis when fitted with a distal attachment.
Silicone Suction Sockets (3S) were first introduced in the mid 1980's. These liners were made of a relatively thin silicone and their primary purpose was suspension of the prosthesis by means of an attachment mounted on the end of the liner that mated with a locking device on the end of the prosthetic socket thereby providing a secure coupling of the residual limb and the prosthesis. PHOTO These liners also offered good protection of the skin against shear forces because the liner didn't move on the skin but rather any movement occurred between the outside of the liner and the adjacent material. Later, thicker liners were developed made of a softer gel that added the benefit of a more even pressure distribution by means of the fluid like characteristics of the gel material flowing from areas of high pressure to areas of lower pressure. Today, these liners are available with or without the distal locking feature. These liners are usually worn in combination with traditional prosthetic socks in order to allow for volume adjustments.
An important consideration in the design and fabrication of a limb prosthesis is the type of material used for its construction. Interface materials will influence the comfort of the socket. Structural materials will affect the strength and weight of the overall prosthesis. The prosthetist has a vast array of materials to choose from in designing the optimal prosthesis for a particular individual. It's important to remember that no one material or type of component is the best for all individuals. Each individual needs to be evaluated with careful consideration given to their lifestyle, expectations and physical characteristics.
Harmony Vacuum Assisted Socket System (VASS)
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The Harmony Vacuum Assisted Socket System (VASS) offers a new concept in prosthetic technology. This system utilizes the proven and effective TEC Interface System with the addition of dynamic vacuum, applied to the socket interface. This system provides excellent suspension and can transport perspiration out of the socket system via the vacuum pump.
Another exciting new development is the microprocessor control of prosthetic knee systems as exemplified by the Otto Bock C-Leg. This system uses an on-board computer to control knee movement providing unprecedented comfort and ease of walking.
Socket geometry is obviously critical to the success of any prosthetic fitting. For the below-knee amputee, total surface bearing designs encourage a socket environment that reduces pressure and thereby improves comfort and control of the prosthesis. For the above-knee amputee, ischial containment designs achieve comfort through careful matching of socket contours to the muscular and skeletal anatomy unique to each amputee. Both types of socket designs are best accomplished through direct casting of the residual limb by an experienced prosthetist.
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