MECHANICAL EVALUATION OF UNITY ELEVATED VACUUM SUSPENSION SYSTEM

BACKGROUND: 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. METHOD: 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. RESULTS: 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. CONCLUSION: 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. Layman’s Abstract: Prosthetic technology innovation is essential to enhance amputee's quality of life because amputation causes a permanent disability and people with limb loss rely on prostheses for the rest of their lives. 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. Recently, the Unity elevated vacuum suspension system (https://assets.ossur.com/library/31882/IFU) was developed by Össur. Understanding of how the Unity elevated vacuum system controls limb movement within the socket, with different socket materials, is important to guide prosthetic prescription. Therefore, mechanical testing was conducted to provide quantitative evidence to guide clinical practice. This study showed that the Unity system can hold the residual limb inside the socket successfully even if there is a failure in the vacuum pump. Elevated vacuum made the socket harder to pull off, which is beneficial in cases where the prosthetic foot is snagged during movement. Article PDF Link: https://jps.library.utoronto.ca/index.php/cpoj/article/view/32941/25960 How To Cite: Gholizadeh H, Lemaire ED, Salekrostam R. Mechanical evaluation of unity elevated vacuum suspension system. Canadian Prosthetics & Orthotics Journal. 2019;Volume2, Issue2, No.5. https://doi.org/10.33137/cpoj.v2i2.32941 Corresponding Author:Hossein Gholizadeh,BSc (P&O), MEng.Sc, PhD,Ottawa Hospital Research Institute, Centre for Rehabilitation Research and Development, Ottawa, Canada.Email: gholizadeh87@yahoo.comORCID: https://orcid.org/0000-0001-5847-798