A few years ago, Amplitude surveyed the latest breakthroughs in “smart sockets,” or sockets that auto-adjust in real time to fluctuations in the size and shape of the residual limb (“Smart Sockets Are on the Horizon,” November/December 2021). Such devices could reduce or eliminate the near-universal aggravations that come with socket misfits, including blisters, sores, rashes, and circulatory problems. They could also decrease the incidence of more serious problems (such as back and joint pain, falls, and prosthesis abandonment) that can occur when poor socket fit affects gait. “If the industry could find a way to consistently improve outcomes in this area,” one source in our article said, “it has the potential to benefit so many of us who just want to go about living our lives without having to stress about how our prosthesis fits on any given day.”
One of the research initiatives cited in that article, the University of Washington’s motor-driven smart socket, has reached the early testing phase—and the results are encouraging. In a new paper published last month in Nature Scientific Reports, the UW team shared the outcomes of an early trial involving an auto-adjusting socket. The prototype device offered two innovative modes of real-time socket adjustment—manual adjustment via a smartphone application, and automated adjustment driven by sensors embedded within the socket. “These advances have the potential to enhance prosthesis users’ quality of life by reducing the mental and physical burdens surrounding routine socket fit adjustments,” the authors concluded.
Smart sockets are difficult to engineer for multiple reasons, but the core conflict boils down to the need for a tight, stable interface between socket and limb that does not irritate or damage soft tissues. The goal is to have the socket loosen just enough—but not too much—when the residual limb expands, and tighten just enough when the limb decreases in volume. To address that challenge, the Washington team designed a socket equipped with motor-driven adjustable panels and sensors that measure fit and walking motion in real time. The device was tested by 12 participants ranging in age from 35 to 78, with a median duration of 17 years post-amputation.
Participants were sent home with the prototype socket and wore it throughout the course of their normal daily routine. They used the device for about a week in each of three distinct modes: auto-adjusting (the socket loosens or tightens on its own, per the sensors’ readings); manual adjustment (the subject uses a smartphone app to loosen or tighten the socket); and locked mode (the socket does not adjust). In both the auto-adjust and manual-adjust modes, socket changes occur while the participant is in motion—they don’t have to sit down or interrupt their gait to adjust the fit.
In all three modes, the researchers collected objective data about the duration each participant wore their prosthesis and the number of daily steps they took. In addition, they gathered subjective data by soliciting the participants’ opinions regarding comfort, ease of use, and other aspects of using the device. Two of the participants did not test the auto-adjust mode, and one chose not to test the locked mode. Here’s a quick summary of the results:
- Six of the 12 participants had their highest daily step counts in auto-adjust mode
- Of the nine participants who tested all three modes, all nine said they got the best fit from either auto-adjust or manual-adjust mode
- Nine of the 12 participants said they would use a smartphone-controlled manual-adjustment feature if one were commercially available
- Nine of the 12 also said they would use a device that monitored and logged socket-fit data in real time
- Ten of 12 stated they if logged socket-fit data were available, they would share it with their prosthetist, physical therapist, and other clinicians
Another key finding was that “manual mode did not facilitate greater walking activity than either auto or locked modes for any participant. An advantage of the auto mode is that the controller monitoring the SFM [socket fit metric] detected changes in socket fit well before participants did, and the controller made small, automated adjustments based on the SFM data to maintain the socket fit. In manual mode, participants made adjustments only when they sensed a detrimental change in fit. In preliminary testing leading up to the present study, we found that some participants did not detect changes in fit until 20 to 30 minutes after a change in SFM occurred. Further, participants using manual model may not have made appropriate size adjustments after sensing a socket fit issue, which could have exacerbated their socket fit problem.”
The mere fact that a smart-socket prototype exists which can be worn all day for normal use is, in itself, a major step forward. This particular device, the early data suggest, achieves the core goal of improving comfort and fit. However, the UW smart socket is still far from a finished product. Most of the participants considered the current version too bulky for practical use; they had a hard time getting their regular clothes over the socket. Another common request was the ability to establish one or more default settings, giving users a few reference points to help them gauge the relative tightness or looseness of the fit. Some expressed the opinion that the auto-adjuster is too sensitive and changes the fit too often.
“The key concepts learned in this study should be applicable to other adaptive sockets and levels of amputation,” this paper concludes. “Future research should carefully consider what participant population each design is intended to serve and create product interfaces, training strategies, and education materials that match users’ individual needs.”
You can read the entire paper online at nature.com/articles/s41598-024-61234-9.
