Introduction: The most suitable elevated vacuum (EV) pressure may differ for each individual prosthesis user depending on suspension needs, socket fit, prosthetic components, and health. The mechanical and physiological effects of EV were evaluated in an effort to determine the optimal vacuum pressure for three individuals.
Methods: Instrumented EV sockets were created based on the participants' regular EV sockets. Inductive distance sensors were embedded into the wall of the socket at select locations to measure limb movement relative to the socket. Each participant conducted an activity protocol while limb movement, limb fluid volume, and user-reported comfort were measured at various socket vacuum pressure settings.
Results: Increased socket vacuum pressure resulted in reduced limb-socket displacement for each participant; however, 81% to 93% of limb movement was eliminated by a vacuum pressure setting of 12 (approximately -9 inHg). Relative limb-socket displacement by sensor location varied for each participant, suggesting distinct differences related to socket fit or residual limb tissue content. The rate of limb fluid volume change and the change in socket comfort did not consistently differ with socket vacuum pressure, suggesting a more complex relationship unique to each individual.
Conclusions: Practitioners may use individual responses to optimize socket vacuum pressure settings, balancing the mechanical and physiological effects of EV for improved clinical outcomes.
Clinical Relevance: Understanding the effects of various socket vacuum pressure settings on individuals' outcomes may improve clinical implementation of EV. In this study, the highest available vacuum setting did not always produce maximum comfort and limb fluid volume benefit, and similar levels of suspension were achieved with lower vacuum settings. (J Prosthet Orthot. 2022;34:194-201)
A comfortable and secure socket fit is critical to a functional lower-limb prosthesis. Obtaining and maintaining optimal socket fit remain challenging for many users, despite advances in socket and suspension technology. Limb volume changes are a key reason why an ideal socket fit is difficult to obtain. As limb volume loss occurs, socket fit degrades, leading to increased motion between the residual limb and socket. Poor socket fit may subsequently result in user discomfort, skin breakdown, gait instability, and even disuse of the prosthesis.
Elevated vacuum (EV) is a suspension method that uses a pump to evacuate the air between the liner and the socket wall, creating negative pressure within the socket. A typical EV system uses an external sleeve to seal the socket proximally. During vacuum application, the liner and residual limb tissues are pulled to the wall of the socket, providing mechanical and physiological benefits. Studies have shown the mechanical effect of EV on reducing limb movement relative to other suspension methods. Physiologically, several studies have suggested that EV better limits limb volume loss compared with suction suspension, particularly during walking and after an accumulation of activity. Elevated vacuum has also been thought to improve overall residual limb health, and several studies have suggested that EV improved functional outcomes and reported satisfaction in prosthesis users.