Prosthetic limbs, clinical review

Prosthetic technology has advanced to a remarkable degree in the past two decades, driven largely by amputees' demand. Today, otherwise healthy individuals with mid-calf amputation should be able to participate in a full range of normal responsibilities, to walk without any perceptible limp, and to engage in recreational and sports activities.

Interface between stump and socket

The single most critical aspect of any prosthesis is the quality of the interface between the limb remnant (stump) and the artificial prosthesis. The portion of the prosthesis that fits snugly over the limb remnant, the "socket," determines the amputee's comfort and ability to control the artificial limb. Since the 1980s prosthetic clinicians and researchers worldwide have made breakthroughs in design and materials that have greatly improved the connection between the socket and stump.

Currently, silicone elastomers are widely used to create a soft and slightly elastic inner liner, providing a thin, comfortable, and compliant barrier between the amputee's skin and the more rigid, weight bearing portions of the prosthetic socket. These socket liners, are usually tethered to the inside of the socket with a mechanical device, termed a shuttle lock, to provide suspension for the prosthetic limb. To remove the artificial limb, the amputee simply presses a concealed button, disconnecting the liner from the socket.
In recent years researchers have developed a variety of thicker gel materials that add a measure of cushioning and pressure dissipation while retaining the benefits of the original liners. The same gel cushioning technology has also been adapted to bicycle seat coverings and similar non-prosthetic applications.

Dynamic response feet with plastic springs

Carbon fibre composites, developed by the aerospace industry, are increasingly being used in artificial limbs, largely because of their superior strength to weight characteristics. One of the most successful innovators has been Flex-Foot, founded by US researcher and amputee Van Phillips. By the 1990s, Flex-Foot's prosthetic foot designs based on carbon fibre springs were widely acknowledged to be the most effective at storing and releasing energy during walking and, in particular, recreational and competitive sports activities. The combination of enhanced socket comfort and prosthetic feet with dynamic response enable amputee medallists in the Paralympics to complete the 100 metre dash within about one second of the Olympic record.

Shock absorbing mechanisms to reduce impact forces

Once amputees worldwide began to regularly jog, run, and jump, it became apparent that the lack of shock absorption in artificial limbs was a limiting factor. Flex-Foot introduced the Re-Flex shin-foot design in 1993, coupling a spring loaded shock absorber with the dynamic response foot. Recently, gait studies have conpracticeed that this type of component improves the biomechanical performance of artificial limbs, which may explain the enthusiastic acceptance of such devices by non-athletes too.

Source - Science, medicine and technology

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