Physiological and Mechanical Effects of Prosthetic Elevated Vacuum Systems in People with Transtibial Amputation

Thesis (Ph.D.)--University of Washington, 2019A major problem among people with a lower limb amputation is maintaining socket fit. Long-term and short-term changes of residual limb volume can alter socket fit resulting in pain, skin breakdown, or falls. Several strategies are used to accommodate the lost volume; however, many of these reduce the size of the socket potentially expediting long-term limb changes. Elevated vacuum (EV) has been used to maintain suspension and manage limb volume by evacuating the air between the prosthetic liner and the socket thus allowing fluid to be drawn into the limb. The physiological and mechanical effects of EV are not well understood as several research studies have evaluated the technique without a clear consensus. The aims of this dissertation were to evaluate the effectiveness of EV to manage limb fluid volume, model the mechanics of EV sockets, and optimize the effects of EV. A goal of this research was to better understand how EV functions and work towards establishing clinical guidelines for its use. The clinical effectiveness of EV to manage daily residual limb fluid volume was evaluated with an in-socket volume measurement technique during a protocol representative of daily activities. Bioimpedance analysis showed that rates of overall fluid volume change were unaffected by EV use compared to suction suspension (SS) with both conditions resulting in median rates of fluid volume loss. However, EV did reduce rates of limb fluid volume change during the final portion of the protocol after an accumulation of daily activity, suggesting benefit for high-activity users. Components of EV sockets such as liner properties, socket fit, and socket vacuum pressure interact to influence the physiological effects of EV such as limb fluid volume change and limb health. A physical benchtop model of an EV socket was developed to evaluate the ability of these EV components to influence physiology and to provide guidelines for clinical implementation of EV. Testing of this model demonstrated the ability to predict tissue vacuum pressure based on individual patient characteristics, prosthetic components, and socket fit. Additionally, the effect of EV on the residual limb tissue was found to be primarily determined by socket fit, while liner properties had minimal effect. Ideal EV parameters may differ for each individual depending on suspension needs, socket fit, prosthetic components, and health. Mechanical and physiological effects of EV were evaluated for optimizing vacuum pressure for three individuals. Multiaxial limb-socket displacement, limb fluid volume change, and user-reported socket comfort were measured at different socket vacuum pressures. Optical coherence tomography (OCT) imaging was used to measure skin perfusion at various tissue vacuum pressures, finding a potential dependency on the state of perfusion prior to vacuum application. Limb-socket displacement was the only metric to change consistently across participants. Changes to limb fluid volume and comfort suggested a more complex relationship unique to each individual. Adjusting socket vacuum pressure to balance the mechanical and physiological effects on individuals could improve EV implementation