Abstract: BACKGROUND: Small residual limb-socket displacement is a good indicator of prosthetic suspensionsystem quality. Active vacuum suspension systems can decrease vertical movement inside the socket,compared to non-active suction systems. This study mechanically evaluated limb-socket displacementwith 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 vacuumconditions (active vacuum, inactive vacuum, no suction with valve open). An Instron 4428 test machineapplied 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, theload 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 forinactive vacuum, and 0.39±0.22mm for no suction. Across all trials, active vacuum systems toleratedsignificantly (p