An adaptive prosthetic socket for people with transtibial amputation.

It is essential that people with limb amputation maintain proper prosthetic socket fit to prevent injury. Monitoring and adjusting socket fit, for example by removing the prosthesis to add prosthetic socks, is burdensome and can adversely affect users' function and quality-of-life. This study presents results from take-home testing of a motor-driven adaptive socket that automatically adjusted socket size during walking. A socket fit metric was calculated from inductive sensor measurements of the distance between the elastomeric liner surrounding the residual limb and the socket's inner surface. A proportional-integral controller was implemented to adjust socket size. When tested on 12 participants with transtibial amputation, the controller was active a mean of 68% of the walking time. In general, participants who walked more than 20 min/day demonstrated greater activity, less doff time, and fewer manual socket size adjustments for the adaptive socket compared with a locked non-adjustable socket and a motor-driven socket that participants adjusted with a smartphone application. Nine of 12 participants reported that they would use a motor-driven adjustable socket if it were available as it would limit their socket fit issues. The size and weight of the adaptive socket were considered the most important variables to improve.

Performance of an auto-adjusting prosthetic socket during walking with intermittent socket release.

Introduction: A challenge in the engineering of auto-adjusting prosthetic sockets is to maintain stable operation of the control system while users change their bodily position and activity. The purpose of this study was to test the stability of a socket that automatically adjusted socket size to maintain fit. Socket release during sitting was conducted between bouts of walking. Methods: Adjustable sockets with sensors that monitored distance between the liner and socket were fabricated. Motor-driven panels and a microprocessor-based control system adjusted socket size during walking to maintain a target sensed distance. Limb fluid volume was recorded continuously. During eight sit/walk cycles, the socket panels were released upon sitting and then returned to position for walking, either the size at the end of the prior bout or a size 1.0% larger in volume. Results: In six transtibial prosthesis users, the control system maintained stable operation and did not saturate (move to and remain at the end of the actuator's range) during 98% of the walking bouts. Limb fluid volume changes generally matched the panel position changes executed by the control system. Conclusions: Stable operation of the control system suggests that the auto-adjusting socket is ready for testing in users' at-home settings.

A sensor to monitor limb depth in transtibial sockets with locking pin suspension: a technical note.

BACKGROUND: Monitoring of limb depth in transtibial sockets may provide useful information toward patient education and care. OBJECTIVE: The objective was to develop a sensor to detect the depth of a locking pin in the shuttle lock of a transtibial socket and to monitor the small motions between ratchet clicks during ambulation. STUDY DESIGN: Controlled bench testing and single-participant study. METHODS: A copper wire coil positioned beneath the socket shuttle lock was used with an inductive sensing chip to monitor locking pin depth. A custom jig was used to calibrate the sensor and bench test the system. Repeatability, drift, and the effects of pin length, carbon fiber presence, temperature change, and pin angulation on sensor performance were tested. Testing was conducted on a participant wearing an adjustable socket, walking with the panels at four different radial positions. RESULTS: The sensor demonstrated a root mean square error of 0.21% of the full-scale output. Different pins, different pin lengths, and the presence of carbon fiber affected calibration, indicating that the sensor must be calibrated to the individual user's socket and pin. Ratchet clicks and cyclic motion between clicks during walking were evident in the data. During participant testing, enlarging the socket at 1.00 mm radial increments caused significant changes in pin peak-to-peak distance (up and down motion) within a step. CONCLUSIONS: The sensor is sufficiently accurate to pursue studies investigating utility of the data toward clinical monitoring of socket fit.

Socket release/relock: An innovative mechanism to maintain residual limb volume.

Management of socket fit is challenging for people using lower-limb prostheses because of residual limb volume fluctuation throughout the day. Releasing socket pressures during sitting (partial doffing) may help users increase their limb volume after they have undergone volume loss earlier in the day. The purpose of this research was to develop and evaluate a system to allow for quick and easy locking pin and socket panel release during sitting and relock upon standing. The system was to allow the partial doff tether length to be custom set for each user, accomplish release and relock in less than 2.0 s each, require only one hand, and require a finger push force comparable to a push button on a phone. A motor-driven release/relock system (<240 g build weight) housed within the socket adjusts locking pin tether length, and an instrumented ratcheting dial adjusts socket panel position. Three participants with a trans-tibial amputation operated the system properly using one hand. For a partial doff, users preferred a tether length between 5 and 6 cm. All users executed release within 1.5 s and relock within 1.5 s.