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

Design and testing of a simple quick connect for a prosthetic liner tether

BACKGROUND

A limitation of tether lanyards is that fastening and unfastening the tether from the liner, which needs to be performed to clean or replace the liner, is difficult for some users.

OBJECTIVE

The purpose of this research was to create a quick connect that allows users to easily attach and detach the tether from the liner.

STUDY DESIGN

Mechanical testing and pilot study.

METHODS

A slide-and-lock mechanism was used. To operate the quick connect, the prosthesis user turns open the lock, slides it onto a short pin extending from the liner, and releases the mechanism, causing it to spring back to the locked position.

RESULTS

Mechanical tests demonstrated that the system well-tolerated tensile loads of 25,000 cycles at 100 N and single cycles at 350 N. Five transtibial users trialed the system and took between 2 and 30 s to fasten and unfasten the quick connect. They found the quick connect intuitive to use, secure, relatively quiet, and stable. However, they preferred their traditional pin lock over the quick connect system, mainly because the quick connect required a multistep procedure (twist-align-slide) that they considered more complex than operating the locking pin to which they were accustomed.

CONCLUSIONS

In its current form, the quick connect is likely to be used by limited community ambulators who struggle with the pin lock donning procedure. It also has potential use with powered tethers that use a motor to adjust tether length.

Short partial doffs of release/relock sockets may effectively stabilize limb fluid volume in prosthesis users with transtibial amputation

BACKGROUND

A challenge often faced by people with lower extremity amputation is management of prosthetic socket fit due to changes in fluid volume within their residual limb. Prior research suggests that intermittently doffing the prosthetic socket may help stabilize daily residual limb fluid volume.

METHODS

To assess the effects of partial doff duration on residual limb fluid volume retention, participants with transtibial amputation were tested by walking on a treadmill in a controlled, laboratory setting under three conditions. An automated system to release the locking pin and enlarge the socket was used to produce the partial doffing. Percent limb fluid volume changes after partial doffing for 4 min (Short Rest) and for 10 min (Long Rest) were compared with no partial doffing (No Release). Limb fluid volume was monitored using bioimpedance analysis.

FINDINGS

Mean percent fluid volume changes in the posterior region were  -1.2% for No Release, 2.7% for Short Rest, and 1.0% for Long Rest. Short and Long Rests had larger increases than No Release (P = 0.005 and 0.03, respectively); Short and Long Rests were not statistically different (P = 0.10). Eight of the thirteen participants experienced a higher percent fluid volume gain for both release protocols while four experienced a higher percent fluid volume gain for only one release protocol.

INTERPRETATION

A partial doff duration as short as 4 min may be an effective strategy to stabilize limb fluid volume in prosthesis users with transtibial amputation. Trials in at-home settings should be pursued.

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.