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The objective of this research was to assess the performance of an embedded sensing system designed to measure the distance between a prosthetic socket wall and residual limb. Low-profile inductive sensors were laminated into prosthetic sockets and flexible ferromagnetic targets were created from elastomeric liners with embedded iron particles for four participants with transtibial amputation. Using insights from sensor performance testing, a novel calibration procedure was developed to quickly and accurately calibrate the multiple embedded sensors. The sensing system was evaluated through laboratory tests in which participants wore sock combinations with three distinct thicknesses and conducted a series of activities including standing, walking, and sitting. When a thicker sock was worn, the limb typically moved further away from the socket and peak-to-peak displacements decreased. However, sensors did not measure equivalent distances or displacements for a given sock combination, which provided information regarding the fit of the socket and how a sock change intervention influenced socket fit. Monitoring of limb–socket displacements may serve as a valuable tool for researchers and clinicians to quantitatively assess socket fit.

A prosthesis user may also make more frequent sock adjustments if fit is not right, or he/she may doff the prosthesis more often or longer to allow fluid volume recovery and offset daily volume loss. How prosthesis users feel about their socket fit and how they accommodate volume changes is important information for practitioners treating patients with limb loss. Practitioners traditionally use self-report information during clinical visits to educate the patient about accommodation methods, make socket adjustments, and determine when a new prosthesis is needed. However, information collected by self-report may be affected by issues such as recall, perception, and social desirability. 3.4 As a result, the practitioner may have to try several different adjustments in order to correct comfort and fit problems. This iterative approach to solving socket fit issues can be time consuming, costly, and potentially detrimental to the prosthesis user's residual limb health. Electronic sensors have been developed to monitor prosthesis use and provide practitioners and patients with an objective record of wear. 5,6 Proximity sensors mounted to the socket brim or embedded within the socket wall have been used previously to detect the presence of the residual limb within the socket. The sensors produced reliable data but consumed too much power to be practical for long-term field use. The purpose of this study was to extend from prior work and develop a portable sensor that measured when the prostheses was donned and doffed and that was capable of long-term (i.e., 2-wk) monitoring. We tested hypotheses that there would be no significant differences between self-report and electronically recorded start of day, end of day, and day durations, and that weekly prosthesis use would differ from weekend prosthesis use among people with transtibial amputation. We also characterized the frequency of socket releases and their durations, as well as doff durations for sock changes using the electronic sensor. From self-report data, we characterized start-of-day sock thicknesses and frequency of sock changes.

Background: Loss of residual limb volume degrades socket fit and may require accommodation. Objectives: To examine if either of two accommodation strategies executed during resting, socket release with full socket size return and socket release with partial socket size return, enhanced limb fluid volume retention during subsequent activity. Study design: Two repeated-measures experiments were conducted to assess the effects of socket release on limb fluid volume retention. Methods: Limb fluid volume was monitored while participants wore a socket with a single adjustable panel. Participants performed eight activity cycles that each included 10 min of sitting and 2 min of walking. The socket’s posterior panel and pin lock were released during the fifth cycle while participants were sitting. In one experiment (Full Return), the socket was returned to its pre-release size; in a second experiment (Partial Return), it was returned to 102% of its pre-release size. Short-term and long-term limb fluid volume retention were calculated and compared to a projected, No Intervention condition. Results: Partial Return and Full Return short-term retentions and Partial Return long-term retention were greater than those projected under the control condition ( p < 0.05). Conclusion: Socket release during resting after activity, particularly when the socket is returned to a slightly larger size, may be an effective accommodation strategy to reduce fluid volume loss in transtibial prosthesis users. Clinical relevance This study suggests that existing prosthetic technologies’ adjustable sockets and locking pin tethers can be used in novel ways to help maintain residual limb fluid volume in active prosthesis users.