AUTO-ADJUSTING PANEL SOCKETS
We recently developed a prosthetic socket for trans-tibial prosthesis users that automatically adjusts its size during walking to maintain prosthetic fit. The auto-adjusting socket is useful to any user who is continually troubled by changes in socket fit. The auto-adjusting socket is designed to allow people to continuously wear their prosthesis pain-free and distraction-free and perform at a high level of function. If you have a trans-tibial amputation and are interested in participating in this research, please click on the GET INVOLVED button at the top right.
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We achieved a socket that auto adjusts its size during walking in 2021 with completion of a take-home study on 13 prosthesis users who compared their test prosthesis in auto-adjustment mode to a manual-adjustment mode and a locked mode. While the controller well maintained a consistent socket fit during walking, most prosthesis users did not spend more than about 5-10% of their prosthesis wear time in walking bouts. Instead, they intermittently moved a few steps, weight-shifted, turned, sat down and stood up, moved around while sitting, etc. Our current goal is to advance our system to auto-adjust during these and other activities to maintain a consistent socket fit over the entire day. This complete system should add to the auto-adjusting socket's impact to enhance the quality of life of people with limb loss.
Project History
The foundation for this project emerged from our prior research efforts Understanding Residual Limb Volume Fluctuation. From clinical studies using a commercial extracellular fluid volume monitoring system (2007.1) and then custom systems that we designed (2016.2; 2019.5), we determined how the auto-adjusting socket should operate. In short, we found:
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Prosthesis users experienced residual limb fluid volume changes over the day, typically volume loss (2012.3)
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Daily residual limb fluid volume change was affected by how tightly users’ sockets fit and their accommodation practices (2017.1; 2018.1)
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Typically, people gained fluid volume: (1) during walking (2014.1; 2019.1), and (2) during sitting right after walking (2004.1; 2012.2; 2016.1), provided the socket size did not restrict limb enlargement
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If the socket was too tight, even for a short time, some prosthesis users did not recover the fluid volume lost earlier in the day (2012.1)
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Secondary co-morbidities, particularly peripheral arterial disease, and smoking tobacco affected the capability for fluid volume recovery during walking (2009.1)
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Prior activity during the day affected present limb fluid volume (2013.1).
It was clear that to achieve a stable daily limb fluid volume, we needed to not only accommodate limb fluid volume loss but also take advantage of opportunities for fluid volume gain. Testing adjustable-panel sockets, we found:
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Prosthesis users did not feel small changes in socket size that were precursors to a deterioration in socket fit (2021.1)
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Small, motor-driven panel adjustments during walking did not de-stabilize fit and were effectively used to control limb fluid volume (2019.2; 2019.3; 2019.7)
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During sitting after walking, releasing the user’s locking pin and enlarging the socket increased limb fluid volume compared with no pin release or socket enlargement (2019.6; 2020.4)
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Pulling the user’s liner outward while walking and while sitting after walking typically increased limb fluid volume compared with no pull (2020.4; 2020.2; 2022.2)
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Using a single-cable adjustable-panel socket was often problematic because sometimes all panels unexpectedly shifted simultaneously and affected fit; a single motor per panel strategy overcame this problem (2021.2)
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Prosthesis users executed a range of socket-adjustment strategies when they were given the opportunity to control their socket size using a phone app (2021.3)
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The control system remained stable despite partial doffing between bouts of automated control walking (2022.1)
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Learning from these results, we programmed our auto-adjusting socket so that it decreased in volume when the residual limb moved away from the socket wall, and it increased in volume when the limb moved closer to the socket wall. Our sensors to detect limb-socket distance are extremely sensitive, picking up the very early signs of changes in socket fit, well before the prosthesis user (2022.1). This early detection is a key reason our efforts have been so successful. The engineering design of our sensors and auto-adjusting socket are described in publication:
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Liner-to-socket distance sensor (2018.2; 2018.3; 2018.4; 2019.8; 2020.3, 2022.3)
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Auto-adjusting socket (2019.4; 2020.1; 2021.2)
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Locking pin depth sensor (2021.4)
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We have continued this research in a collaboration with The Center for the Intrepid at the Brooke Army Medical Center in San Antonio to test the auto adaptable socket in a military simulation environment.
Publications
2022.3. "Using magnetic panels to enlarge a transtibial prosthetic socket." (submitted)
2022.2. "Cyclic socket enlargement and reduction during walking to reduce limb fluid volume loss in transtibial prosthesis users."
2022.1. "Performance of an auto-adjusting prosthetic socket during walking with intermittent socket release."
2021.4. "A sensor to monitor limb depth in transtibial sockets with locking pin suspension: A technical note."
2021.3. "Adjusting socket size using a cell phone app: Observations from participants with transtibial amputation."
2021.2. "Automatic control of prosthetic socket size for people with transtibial amputation: Implementation and evaluation."
2021.1. "Performance of a sensor to monitor socket fit: Comparison with practitioner clinical assessment."
2020.4. "Fluid volume management in prosthesis users: Augmenting panel release with pin release."
2020.3. "Incorporating a ferrous polymer target into elastomeric liners for socket fit sensing in prosthesis users."
2020.2. "Does actively enlarging socket volume during resting facilitate residual limb fluid volume recovery in trans-tibial prosthesis users?"
2020.1. "An algorithm to calculate socket volume changes of adjustable sockets for transtibial prosthesis users."
2019.8. "Thin magnetically permeable targets for inductive sensing: Application to limb prosthetics."
2019.7. How do transtibial residual limbs adjust to intermittent incremental socket volume changes?
2019.6. Adjustable sockets may improve residual limb fluid volume retention in transtibial prosthesis users."
2019.5. A portable bioimpedance instrument for monitoring residual limb fluid volume in people with transtibial limb loss: A technical note."
2019.4. "A motor-driven adjustable prosthetic socket operated using a mobile phone app: A technical note."
2019.3. "Socket size adjustments in people with transtibial amputation: Effects on residual limb fluid volume and limb-socket distances."
2019.2. "How do socket size adjustments during ambulation affect residual limb fluid volume? Case study results."
2019.1. "Effects of activity intensity, time, and intermittent doffing on daily limb fluid-volume change in people with transtibial amputation."
2018.4. "An inductive sensing system to measure in-socket residual limb displacements for people using lower-limb prostheses."
2018.3. "Development of a magnetic composite material for measurement of residual limb displacements in prosthetic sockets."
2018.2. "Instrumented socket inserts for sensing interaction at the limb-socket interface."
2018.1. "Residual limb fluid volume change and volume accommodation: relationships to activity and self-report outcomes in people with trans-tibial amputation."
2017.1. "Effects of socket size on metrics of socket fit in trans-tibial prosthesis users."
2016.2. "A bioimpedance analysis platform for amputee residual limb assessment."
2016.1. "Does temporary socket removal affect residual limb fluid volume of trans-tibial amputees?"
2014.1. "How do activities walking, standing, and resting influence trans-tibial amputee residual limb fluid volume?"
2013.1. "Influence of prior activity on residual limb volume and shape measured using plaster casting: Results from people with trans-tibial limb loss."
2012.3. "Preliminary investigation of residual-limb fluid volume changes within one day."
2012.2. "Post-doffing residual limb volume change in people with trans-tibial amputation."
2012.1. "How do sock ply changes affect residual limb fluid volume in people with trans-tibial amputation?"
2009.1. "Clinical utility of in-socket residual limb volume change measurement: Case study results."
2007.1. "Assessment of residual-limb volume change using bioimpedence."
2004.1. "Shape and volume change in the transtibial residuum over the short term: Preliminary investigation of six subjects."
RELEASE-RELOCK SOCKETS
This is a technology that allows prosthesis users to quickly and discretely release their socket pressures upon sitting and then relock their socket in preparation for standing. We created this technology in response to users who complained about socket discomfort when sitting in long meetings, at a conference table at work for example. They wanted a quick and discrete method for releasing and relocking their locking pin. The technology is also relevant to residual limb volume management. We have shown that intermittently releasing socket pressures during the day helps to stabilize daily limb fluid volume in many prosthesis users.
Project History
To design this technology, we incorporated knowledge gained from our efforts Understanding Residual Limb Volume Fluctuation. Those findings included:
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Prosthesis users gained more fluid volume after releasing socket pressures right after walking than right after sitting (2012.1)
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Doffing the socket for 30 minutes between bouts of walking significantly increased limb fluid volume in the walks after the doff, whether the liner was removed or not (2016.1)
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In a study on 29 prosthesis users, non-accommodators (people who did not add socks) spent more time with their prosthesis doffed and reported better outcomes than accommodators (people who did add socks) (2018.1)
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Socket users with pin suspension experience less posterior fluid volume loss over a 6-hour test protocol when they intermittently doffed their prosthesis than when they did not doff their prosthesis (2019.1)
We developed a series of release-relock designs, starting with a seat-belt mechanism for tether retraction (2018.2) and then moving to a motor-driven take-up reel housed in the distal end of the socket and then to a microprocessor-controlled unit (2021.1). Testing prototypes of our release-relock system, we found:
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Users had little tolerance for a system that drew the tether in slowly
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Tether release distance needed to be set for the individual user, but most users preferred a tether length between 3 and 5 cm (2019.2)
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Users would have preferred a simpler, lower dexterity mechanism than the threaded fastener to connect the tether to the liner, particularly users who adjusted their sock ply during the day (2018.2)
When we used the release-relock simultaneously with an adjustable panel socket, we found:
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Some people induced considerable tension in their tether/locking pin while sitting; understanding how this tension affects residual limb health is a topic we believe worthy of further investigation
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Releasing socket panels simultaneously with tether release enhanced fluid volume gain over panel release alone in the long-term (2020.1)
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Most people preferred to first don their residual limb deep into the socket and then tighten the panels. Users with much redundant soft tissue in their residual limb preferred tightening the panels first and then donning (2019.2)
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In 11 of 12 prosthesis users tested to date, intermittent doffing and panel release for 4 min and/or 10 min significantly enhanced limb fluid volume compared with no release (2022.1)
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Using the insight gained from these investigations, we conducted a series of take-home studies. Prosthesis users wore a test prosthesis in their free-living environment for about 2.5 weeks with the release-relock active and 2.5 weeks with the motor unit replaced with a traditional pin lock system of the same weight. Prosthesis use, socket fit, and self-reported outcomes are compared for the two conditions.
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Publications
2022.2. "How does a release-relock socket impact prosthesis use and self-reported outcome in take-home testing?" (in preparation)
2022.1. "Release-relock sockets for transtibial prosthesis users: Release duration and residual limb volume." (submitted)
2021.1. "Socket release/relock: An innovative mechanism to maintain residual limb volume."
2020.1. "Fluid volume management in prosthesis users: Augmenting panel release with pin release."
2019.2. "Adjustable sockets may improve residual limb fluid volume retention in transtibial prosthesis users."
2019.1. "Effects of activity intensity, time, and intermittent doffing on daily limb fluid-volume change in people with transtibial amputation."
2018.2. "Retracting locking-pin mechanism that allows partial socket doffing during sitting."
2018.1. "Residual limb fluid volume change and volume accommodation: Relationships to activity and self-report outcomes in people with trans-tibial amputation."
2016.1. "Does temporary socket removal affect residual limb fluid volume of trans-tibial amputees?"
2012.1. "Post-doffing residual limb volume change in people with trans-tibial amputation."
ELEVATED VACUUM SOCKETS
Initial efforts using our novel limb fluid volume monitoring system to understand if and how elevated vacuum systems stabilized limb fluid volume showed inconclusive results (2011.1). This was in part because of difficulty maintaining vacuum pressure for the duration of the study, We found elevated vacuum finicky, as other researchers had experienced. Small leaks in the outer sleeve or in the socket itself made it difficult to maintain high levels of vacuum. Dr. Robert (Ty) Youngblood in his PhD dissertation work undertook an exceptionally well designed and well executed study to better understand elevated vacuum systems. Working with Mr. Richard Foster, a prosthetist in Oklahoma with extensive experience effectively fitting patients with EV sockets, we eliminated the leakage problems and conducted a clinical investigation.
Project History
Coming soon
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Publications
2022. "An instrumented printed insert for continuous monitoring of distal limb motion in suction and elevated vacuum sockets." (in preparation)
2021.1. "Mechanically and physiologically optimizing prosthetic elevated vacuum systems in people with transtibial amputation: a pilot study."
2020.2. "Modeling the mechanics of elevated vacuum systems in prosthetic sockets."
2020.1. "Effectiveness of elevated vacuum and suction prosthetic suspension systems in managing daily residual limb fluid volume change in people with transtibial amputation."
2011.1. "Effects of elevated vacuum on in-socket residual limb fluid volume: Case study results using bioimpedance analysis."
Project History
The project emerged in part from our initial efforts in 2001 testing the mechanical performance of air-inflated inserts (2001). We found that the volume range over which inserts provided good mechanical support was narrow. This was due in part to the compressible medium - air. We therefore moved on to liquid-filled inserts. When we tested liquid-filled inserts taped to the insides of the socket on people with transtibial amputation, we found that adding liquid to the inserts tended to drive fluid out of the residual limb, and most participants did not well-recover that fluid volume (2013). The inserts we used were bulky, and we believed that a more effective design would be to embed the inserts into the liner. Is was clear that the next step was to try a liner-embedded dynamically-adjustable insert. We therefore moved onto the project with Sandia.
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Initial testing demonstrated that the Sandia liner effectively relieved socket stresses during sitting. A measurable increase in residual limb fluid volume over use of a regular liner was shown (2016.1).
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Subsequently, Sandia developed a novel three-directional interface stress sensor and embedded it within the liner (2016.2). When we tested it on people with transtibial amputation, however, it was difficult to identify features in the data that matched with a change in prosthetic fit (CDMRP Final Report for Project MIPR0LDATM0147). We concluded that interface stress might not be an appropriate feedback variable for control of an auto adjusting socket.
SANDIA BLADDER LINER SOCKETS
This project was a collaboration with Jason Wheeler PhD and his group at the Sandia National Laboratories in Albuquerque. The intent was to develop a prosthetic liner with embedded liquid-filled inserts, and to test a novel three-directional interface stress sensor that Sandia had previously developed. The entire system could potentially be used in a controlled system where bladder liquid volume was adjusted based on interface stress sensor data to maintain a consistent socket fit.
Publications
2016.2. "A pressure and shear sensing liner for prosthetic sockets."
2016.1. "Preliminary evaluation of a novel bladder-liner for facilitating residual limb fluid volume without doffing."
2013. "How does adding and removing liquid from socket bladders affect residual-limb fluid volume?"
2001. "Mechanical performance of inflatable inserts used in limb prosthetics."