Motorized Prostheses for Lower-limb Amputees

AIM1:

For all studies, participants will repeat the same experimental protocol with their passive prostheses and our lightweight powered knee combined with powered, semi-active, and passive ankle. The investigators will also administer a questionnaire based on a 5-point Likert scale to rate intuitiveness, safety, physical demand, and mental demand for each tested condition. Participants will have time to familiarize themselves with the protocol and the prosthesis in a separate training session.

Part 1: Level and Inclined Walking Effort. The study will assess walking effort as participants walk on an instrumented treadmill at their self-selected comfortable speed. The primary outcome of the first study will be residual limb effort measured through peak hip flexion torque on the prosthesis side. Secondary outcomes will include contralateral leg effort, gait symmetry, and balance. The experimental protocol will be repeated for different inclines (e.g., 0%, +/-10%) during separate experimental sessions.

Part 2: Ambulation on Stairs. The study will analyze speed and effort during stair ascent and descent. Participants will ambulate on an instrumented staircase that includes seven steps (four instrumented). The primary outcome for stair ascent will be the ratio between prosthesis work and residual limb work, whereas, for stair descent, the investigators will use sound knee and ankle work. Residual limb, contralateral leg, and upper body effort (handrail force) will be the secondary outcomes, together with subjective preference.

Part 3: Sit-to-Stand Transitions. This study will assess biomechanics as the participant transitions between sitting and standing. Participants will perform sit-to-stand and stand-to-sit transitions from a chair with no armrests at their self-selected pace. The investigators will assess full-body biomechanics similar to our previous sit-to-stand and stand-to-sit studies. The primary outcome of this study will be the degree of asymmetry.

AIM2:

Participants will repeat the experimental protocols with their prescribed prostheses and our lightweight powered prosthesis using direct electromyographic control and indirect volitional control. The experiments will be conducted in a motion capture lab to assess full-body kinematics and kinetics. The investigators will also administer a questionnaire based on a 5-point Likert scale to rate intuitiveness, safety, physical demand, and mental demand for each tested condition. Participants will have time to familiarize themselves with the protocol and the prosthesis controllers in dedicated training sessions.

Part 1: Inclined Walking at different speeds and loading conditions. This study will assess the ability to walk at various speeds on inclines/declines while carrying objects. To this end, participants will walk on an instrumented treadmill both at their self-selected speed and 130% of their self-selected speed with and without holding a 20-lb load in both hands. The difference between hip peak torque on the sound and prosthesis sides will be used as a primary outcome. Secondary outcomes will include gait symmetry, balance, and subjective preference. During separate sessions, the experimental protocol will be repeated at 10% incline and 10% decline.

Part 2: Stair Climbing at different speeds and loading conditions. This study will assess the ability to ascend and descend stairs under different speeds and loading conditions. Participants will ascend an instrumented staircase at comfortable and fast self-selected speeds. Participants will climb stairs at both speeds with and without a 20-lb object carried in their hands or a backpack. The difference between knee peak torque on the sound and prosthesis sides will be used as a primary outcome. Secondary outcomes will include contralateral leg effort, gait symmetry, and balance.

Part 3: Stand up, Squat, Lunge, and Kneel. This study will assess the ability to stand up, squat, and lunge under different loading conditions. Participants will perform five repetitions of sit-to-stand transfers. Then, they will squat, lunge, and kneel five times. The primary outcome will be prosthesis weight-bearing. Secondary outcomes will include time to completion, joint effort, and subjective preference.

AIM3:

Participants will repeat the experimental protocols with their prescribed prostheses and our lightweight powered prosthesis. During dedicated training sessions, they will have time to familiarize themselves with the protocol.

Part 1 Ambulation Circuit. Participants will perform ten trials of the ambulation circuit. Starting in a chair, standing up, walking to a 4-step staircase, climbing up the stairs to an elevated platform, continuing to walk on the platform, turning, descending an intermediate platform using a two-step staircase, descending a ramp, walking to the chair, and ending by sitting down. Next, ten trials of the reverse circuit will be completed, starting with sitting in the chair and ending with the ramp ascent. The primary outcome will be the average time to complete the circuit. Secondary outcomes will be joint kinematics during transitions and subjective preference.

Part 2: Self-Selected Walking Speed. Participants will perform the timed 10-meter walking test on a self-paced instrumented treadmill. Walking speed will be the primary outcome. Secondary outcomes will include spatiotemporal gait symmetry and subjective preference.

Part 3: Amputee Mobility Predictor. This study aims to assess clinical outcome measures using the Amputee Mobility Predictor, a reliable performance measure validated for those with lower-limb loss, to identify limitations in prosthetic mobility and measure several functional mobility tasks needed during daily living activities.

Part 4: Real-World Mobility. This study will provide a quantitative assessment of mobility in complex home and community environments. To this end, the investigators will measure performance and satisfaction while participants perform common activities of daily living, which will include household chores (mopping floors, making beds, cooking, grocery shopping) and leisure activities (walking the dog, strolling in a park, gardening). Subjective preference will be the primary outcome and will be assessed by administering a questionnaire with separate ratings for intuitiveness, safety, physical demand, and mental demand. The secondary outcome will be kinematics, which the investigators will assess using an IMU-based motion capture system.

Our inclusion criteria will be

• Above-knee amputation
• K2/K3/K4 ambulators
• At least 18 years old
• At least one year since amputation
• At least six months since the definitive prosthesis fitting
• Currently prescribed and using a mechanically passive or microprocessor-controlled prosthesis

Our exclusion criteria will be

• Over 350 lbs. body weight, the weight limit for our safety suspension systems
• Cognitive deficits or visual impairment that could impair their ability to give informed consent or to follow simple instructions during the experiments
• Pregnant women due to elevated safety concerns for this population
• Co-morbidity that limits their ability to participate in the study protocol (e.g., stroke, pacemaker placement that would interfere with the powered prosthesis, severe ischemia, cardiac disease, etc.)
• Adults who are unable to consent
• Individuals who are not yet adults (infants, children, teenagers)
• Individuals who use a wheelchair for mobility both outdoors and indoors because they may not be able to perform the necessary activities with their passive prosthesis or the powered prosthesis
• Prisoners, due to concerns with informed consent