The Prosthetic Engineering research at the Center explores the complex relationship between prosthetic interventions and the people who wear them. Our aims include improving prosthetic prescriptions by investigating the efficacy of prosthetic components used in current clinical practice and by developing novel approaches intended to improve the current standard of care. During 2009, our Veteran amputee research focused on: mobility, injury prevention, and amputee comfort and sensation.

Mobility of Veteran Lower Limb Amputees

Helping lower limb amputees walk farther can have a dramatic influence on their lives and need for support services. The ability to walk a few hundred more steps per day can change a household ambulator to a community ambulator. One factor that can influence mobility involves the stress applied to residual limb tissue.

Turning and Maneuvering. Turning and maneuvering occur frequently throughout the day in both the household and community environments. Our previous work in this area explored whether or not a commercially-available transverse plane torsion adapter would enhance (or hinder) the ability of amputees to perform turning maneuvers.

Findings: Our measurements of Veteran amputees using these adapters indicate they reduce transverse plane torques, suggesting lower residual limb torsional stresses and reduce incidence of soft tissue injuries. An open question remains: how compliant should these transverse plane torsion adapters be? Too stiff and there is no benefit. Too compliant and the Veteran amputee feels unstable. In 2009, we built and bench-tested a second generation device whose stiffness can be automatically controlled. We are currently recruiting Veteran amputees to test this device.

Another factor that can influence mobility is an amputee’s confidence in their walking ability. If they are afraid they might fall, they walk much more slowly and cautiously.

Disturbance Response in Amputee Gait. Gait disturbances are a fact of life; you get jostled walking in a crowd or inadvertently bump into an obstacle. Stepping on uneven terrain can also make a person vulnerable to a fall. Our research seeks to understand how non-amputees and lower limb amputees recover from a disturbance.

Findings: Our results indicate non-amputees employ an ankle inversion-eversion strategy to maintain balance. Unfortunately, this ankle strategy is currently unavailable to lower limb amputees. Our work in 2009 resulted in a first generation prototype prosthetic ankle that can invert and evert. Our bench-tests are refining the control algorithms and we expect to conduct human subject tests in 2010.

Injury Prevention for Veteran Lower Limb Amputees

Preventing injuries to the residual limb is foremost on the minds of lower limb amputees. Short bouts of strenuous activities (e.g., jumping, running) can increase the stresses applied to skin tissues while long bouts of usual activities (e.g., walking) can increase the dose. Recovery from higher stresses or larger doses is predicated by tissue health, which is directly related to the tissue oxygen levels.

Socket System Effect on Tissue Oxygenation during Amputee Gait. The aim of our research in this area is to develop and use novel instrument capable of measuring residual limb tissue oxygenation inside a prosthetic socket while the amputee is standing and walking

Findings: In 2009, we completed instrument development and are recruiting Veteran amputees wear four different socket and suspension systems. We expect the results to provide clinically-relevant evidence to guide prescription practice. Prostheses that provide higher levels of tissue oxygenation will likely reduce the incidence of injury and speed recovery when injuries occur.

Vacuum Socket Suspension. Many amputees live with an ill-fitting socket and can experience limb pistoning within the socket, which in turn may result in skin irritation and injury. Vacuum-assisted suspension systems may alleviate these conditions by making the limb expand to fit the socket.

Findings: Our results indicate vacuum-assisted suspensions reduce limb pistoning but Veteran amputees are more active while wearing pin suspensions. They also prefer the pin suspension to the vacuum-assisted suspension. While encouraging, our results suggest further work is needed on vacuum-assisted technologies.

Comfort and Sensation of Veteran Lower Limb Amputees

Our research on amputee comfort and sensation includes efforts to understand the thermal environment at the skin-prosthesis interface and develop interventions that improve the comfort of veteran amputees. We are developing an instrument that can measure the vasomotor response to controlled changes in tissue temperature in diabetic individuals. The results from this research will aid our efforts to define the design requirements of a thermally-controlled prosthetic socket.

Mechanically-induced Stochastic Resonance to Improve Amputee Gait. Amputees with diminished peripheral limb sensation often have difficulty maintaining posture and stable gait. The idea of enhancing sensation in these patients through introduction of sub-threshold vibration is counterintuitive because the presence of noise usually degrades performance, yet the ability to enhance sensory feedback through stochastic resonance and improve postural stability and ambulation in both healthy and diseased intact individuals has already been demonstrated.

Findings: In 2009, we tested nearly a dozen Veteran amputees and found sub-threshold vibration had little effect on their balance while standing. We expect to complete our tests on dynamic balance (while walking) in 2010 but believe this technology needs further refinement before introducing it into clinical practice.

Future Directions for Research for Veteran Amputees

Our multi-disciplinary research team is continuously pursuing new innovations and novel approaches to improving the health and mobility of veteran amputees. During 2010, our work will include:

1. testing an inverting-everting ankle thought to improve balance and stability,
2. testing a prosthetic limb whose torsional characteristics can be controlled using both biological and environmental based input signals,
3. testing a novel socket system that can remove perspiration and provide evaporative cooling,
4. a within-pylon data acquisition and storage system capable of measuring environmental, physiological, diagnostic, and activity-based metrics, and
5. developing electromyographic approaches to controlling lower limb systems.