Functional Performance Evaluation of the Northwestern University Flexible Sub-Ischial Vacuum (NU-FlexSIV) Socket for Persons with Transfemoral Amputation

Project: Research project

Project Details


Focus Area & Military Benefit: We propose a Clinical Trial focused on functional performance evaluation of the prosthetic socket we developed with an FY09 PRORP Technology Development Award (Proposal #OR090122, Award #W81XWH-10-1-0744) titled, “Development of Sub-Ischial Prosthetic Sockets with Vacuum-Assisted Suspension for Highly Active Persons with Transfemoral Amputations.” The availability of a more comfortable and functional socket will contribute to improving the quality of life of persons with transfemoral amputation, especially military persons with amputation who are typically young, with excellent premorbid health, and who wish to return to premorbid activity levels, resulting in higher functional expectations.1 Background: Prosthetic sockets form the interface between the residual limb and prosthesis. Although they are designed to support the body and enable effective biomechanical load transfer during walking and other activities.2 the residual limb tissues are neither accustomed nor well-suited to the high pressure and shear loading that occurs during ambulation with a prosthesis.3 Despite high daily use (≥12 hours), lack of socket comfort is the commonest complaint of prosthesis users.4-7 Most prosthetic sockets are rigid despite transfemoral residual limbs being comprised of large masses of compliant soft tissues surrounding the amputated bone that change shape with movement and muscular activity.8 During muscular contractions, residual limb shape change results in high stresses at the socket/limb interface. Flexible sockets provide a mechanism to potentially attenuate and disperse these high stresses from the limb, improving comfort. Additionally, current transfemoral socket designs (e.g. the ischial containment socket, Fig. 1a) encase the hip joint and portions of the pelvis, limiting range of motion at the hip and compromising comfort.9,10 In contrast, the NU-FlexSIV Socket (Fig. 1b) does not impinge on the pelvis because it has lower proximal trim lines (Fig. 1c-e); is highly flexible (Fig. 1f) allowing muscles to move comfortably within the socket as they contract during activity and improving sitting comfort; and is held securely to the residual limb by suction from a vacuum pump, making for a firmer connection to the prosthesis than other forms of suspension.11 The NU-FlexSIV Socket is a sub-ischial socket with a rigid frame embedded within two flexible lamination layers (Fig. 1f). Hypothesis & Approach: We propose an assessor-blinded randomized cross-over trial comparing functional performance with the NU-FlexSIV Socket to the standard-of-care ischial containment socket in persons with unilateral transfemoral amputation. We hypothesize that the NU-FlexSIV Socket will provide increased comfort (primary end point) and better functional performance (secondary end points) compared to the ischial containment socket. Comfort will be assessed using the Socket Fit Comfort Score.12 Functional performance will be assessed using instrumented motion analysis to record biomechanics of walking at different speeds, a 5-time Rapid Sit-to-Stand Test, our-Square-Step Test, and T-test of Agility.13,14 The Orthotic and Prosthetic Users’ Survey (OPUS)15 will be used to assess additional patient reported outcomes related to lower extremity functional status, health related quality of life, and satisfaction with device. Since accommodation to sockets is unknown, data will be collected at baseline (within one week of socket fitting) and after 3 and 6 weeks of every day socket use (time points chosen to enhance subject retention).
Effective start/end date9/30/159/29/20


  • U.S. Army Medical Research and Materiel Command (W81XWH-15-1-0708)


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