Abstract
Small residual limb-socket displacement is a good indicator of prosthetic suspension system quality. Active vacuum suspension systems can decrease vertical movement inside the socket, compared to non-active suction systems. This study mechanically evaluated limb-socket displacement with the Össur Unity active vacuum system. Forty-eight conditions were evaluated: four cylindrical and four conical sockets (polypropylene, polyethylene terephthalate glycol-modified (PETG), thermoset resin (acrylic), Thermolyn soft materials); two Iceross Seal-In V liners (standard, high profile); three vacuum conditions (active vacuum, inactive vacuum, no suction with valve open). An Instron 4428 test machine applied 0-100N linear ramped tensile loads to each positive mold, with the socket secured in place, while displacement between the mold and socket was recorded. Following the displacement tests, the load before failure (i.e., 10 mm displacement) was measured. Average and standard deviations for movement between the mold and sockets were small. The displacement average for all conditions was 0.30±0.16mm for active vacuum, 0.32±0.16mm for inactive vacuum, and 0.39±0.22mm for no suction. Across all trials, active vacuum systems tolerated significantly (p<0.001) more load before failure (812±221N) compared to inactive vacuum (727±213N), and no suction (401±184N). The maximum load before failure (1142±53N) was for the cylindrical polypropylene socket and high-profile liner. The Unity system successfully controlled pistoning inside the socket for regular activity loads and also controlled the greatest traction loads. While relative movement was smallest for Unity, all conditions (inactive vacuum, no suction) were viable for loads less than 100N. Furthermore, similar results can be achieved when using different socket fabrication materials.
Highlights
The method for attaching a prosthesis to the body is termed prosthetic suspension
While relative movement was smallest for Unity, all conditions were viable for loads less than 100N
Less movement was measured with conical socket shapes (0.28±0.16mm) compared to cylindrical sockets (0.33±0.17mm) in active vacuum condition when 100N traction load applied
Summary
The method for attaching a prosthesis to the body is termed prosthetic suspension. Selecting a suitable suspension system is an important step in the prosthetic rehabilitation process.[1,2,3,4] A better understanding of prosthetic suspension systems may facilitate selection based on the amputee’s needs, leading to better socket system performance.[2,5,6] Small residual limb-socket displacement is a good indicator of prosthetic suspension system quality.[7,8]Various prosthetic suspension approaches are used in clinical practice. A thigh corset was traditionally used for suspension, but introduction of the patellar-tendon bearing prosthesis lead to other suspension methods; such as, cuff, supracondylar-suprapatellar, and suprapatellar strap.[2,6] The Icelandic roll-on silicone socket (ICEROSS) system was introduced to the rehabilitation market to improve suspension via close adhesion of the silicone liner to the residual limb skin.[2,6] Various methods are used to hold the silicone liner inside the prosthetic socket; including, single distal pin/lock, lanyard, suction, seal-in, or vacuum. Small residual limb-socket displacement is a good indicator of prosthetic suspension system quality. This study mechanically evaluated limb-socket displacement with the Össur Unity active vacuum system.
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