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Effects of a modified passive socket system on short-term changes in residuum volume and comfort: A preliminary study in transtibial amputees

Background: Changes in residuum volume are a common problem in lower-limb amputees during prosthesis usage, and can lead to poor suspension, impaired gait, and tissue damage. Residuum volume can be affected by the in-socket air pressure, which will influence fluid flow in and around the residuum. The use of “active” pumps to reduce air pressure has been shown to conserve the residuum volume, but these are expensive and unlikely to be widely available. An alternative, passive approach, based on Boyles' law, is to introduce a larger distal void volume at the end of the socket and hence reduce the change in pressure for a given change in volume. Objectives: To compare the performance across three test conditions (passive—conventional, with standard distal void; passive—with increased distal void; and active system) in terms of residuum volume changes and comfort. Study design: Repeated-measures experiment under three test conditions. Methods: Five transtibial amputee participants (three males and two females), aged between 27 and 67 years, and of mobility grade K2 or K3, were fitted with a bespoke test prosthesis that was adapted to include the three test conditions. Residuum volume was measured before and after walking under each test condition (presented in a random order). Comfort was also assessed after walking with each test condition. Results: The reduction in residuum volume, relative to the baseline volume, was higher for the conventional passive system (4.2% ± 2.8%) compared with the modified passive (1.4% ± 1.4%) and active (1.6% ± 1.1%) systems. Conclusion: The use of a passive suspension system with an increased distal void within the socket may help to stabilize the residuum volume during prosthesis usage.