The redesigned LFMS coil is substantially smaller and more energy-efficient than the original, improving cost, power consumption, and portability. These improvements could facilitate deployment of LFMS in the clinic and potentially at home. This coil redesign approach can also be applied to other magnetic stimulation paradigms. Finally, the anatomically-accurate E-field simulation of LFMS can be used to interpret clinical LFMS data.

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.

The purpose of this research was to create a thin ferrous polymer composite to be used as a target for inductive sensing in limb prosthetics. Inductive sensors are used to monitor limb-to-socket distance in prosthetic sockets, which reflects socket fit. A styrene–ethylene–ethylene/propylene–styrene (SEEPS) polymer was mixed with iron powder at three concentrations (75, 77, 85 wt%), and thin disk-shaped samples were fabricated (0.50, 0,75, 1.00 mm thickness). For 85 wt% samples of 0.50 mm thickness, which proved the best combination of high signal strength and low target volume, inductive sensor sensitivity ranged from 3.2E5 counts/mm at 0.00–1.00 mm distances to 7.2E4 counts/mm at 4.00–5.00 mm distances. The application of compressive stress (up to 425 kPa) introduced an absolute measurement error of less than 3.3 μm. Tensile elasticity was 282 kPa, which is comparable to that of commercial elastomeric liners. Durability testing in the shoe of an able-bodied participant demonstrated a change in calibration coefficient of less than 3.8% over two weeks of wear. The ferrous polymer composite may facilitate the development of automatically adjusting sockets that use limb-to-socket distance measurement for feedback control.

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.