Automatic Prosthetic Foot Stiffness Modulation to Improve Balance in the Real World

Automatic Activity-Dependent and Phase-Varying Prosthetic Foot Stiffness Modulation to Improve Balance Control in Individuals With Lower-Limb Amputations in the Real World

The goal of this clinical trial is to determine if automatic stiffness modulation improves balance control in ambulatory individuals with below-knee amputations in real-world conditions. The main question this clinical trial will answer is:

• Can a user-specific automatic stiffness prosthesis improve balance control compared to user's fixed stiffness prosthesis that was clinically prescribed?

Participants will perform free-ranging ambulatory activities outside the laboratory that include nine ambulatory activities of daily living (walking at different speeds, turning, ramp ascent/descent, while carrying a load, and while walking on uneven terrain) while wearing, in random order, 1) a fixed stiffness prosthesis that was clinically prescribed and 2) an automatic stiffness prosthesis that uses an open source ankle configured to implement a user- and activity-specific automatic stiffness modulation control scheme intended to improve balance control.

Study Overview

• Status: Not yet recruiting
• Conditions: Lower Limb Amputation Below Knee
• Intervention / Treatment: Device: Fixed stiffness prosthesis; Device: Automatic stiffness prosthesis

Detailed Description

Individuals with lower limb amputations are at higher risk of falling compared to able-bodied and other clinical populations and are more likely to sustain life-altering injuries. The higher fall risk is primarily due to the loss of muscles crossing the ankle, which are critical to maintaining balance control. Prosthetic devices are designed to provide appropriate stiffness for needed stability and support. While research has shown the optimal stiffness to maintain balance varies across ambulatory activities (e.g., straight walking versus turning), most clinically prescribed prosthetic devices are passive and only provide a fixed stiffness level. The one commercially available, powered prosthetic ankle-foot, has not been shown to restore balance control. Thus, a prosthetic device that actively adjusts ankle stiffness across different ambulatory activities is critically needed to advance the field and improve balance control for those with lower-limb amputations. The goal of this clinical trial is to identify prosthesis stiffness that optimizes balance control in individuals with below knee amputations as they perform typical ambulatory activities of daily living. By matching the ankle stiffness to the task requirements, the investigators believe balance control will significantly improve and fall risk will decrease for those with lower-limb amputations.

Each participant will be fit with a novel prosthesis that includes a low-profile prosthetic foot whose stiffness category will be determined by their body weight and activity level (standard clinical practice), a prosthetic foot whose stiffness category is two categories stiffer, and another whose stiffness is two categories less stiff. Participants will continue to use their existing prosthetic socket and suspension system, but their pylon length will be adjusted as needed. While wearing the different study prostheses in randomized order, nine ambulatory activities will be performed in a motion capture laboratory.

1. Walking on level ground at self-selected speed.
2. Walking on level ground at 15% slower than self-selected speed.
3. Walking on level ground at 15% faster than self-selected speed.
4. Walking up an 8% slope at self-selected speed.
5. Walking down an 8% slope at self-selected speed.
6. Walking on level ground at self-selected speed while carrying a 5 kg load in one hand on their prosthetic side.
7. Walking on level but uneven terrain at self-selected speed.
8. Walking around 2-meter diameter circle at self-selected speed with the prosthetic side on the inside of the circle.
9. Walking around 2-meter diameter circle at self-selected speed with the prosthetic side on the outside of the circle.

Ambulatory activities 1 through 6 will be performed on an instrumented treadmill. The load to be carried in activity 6 will be configured as a grocery bag with handles. Activity 7 will be performed on a rocky terrain treadmill. Activities 8 and 9 will be performed overground across five force plates embedded in the laboratory floor while following the outline of a 2-meter diameter circle. Rest breaks during all activities will be provided as needed.

The data from this experiment will be used to calculate the peak-to-peak range of the frontal plane whole-body angular momentum (a measure of balance control). The investigators will use these calculations to determine a user- and activity-specific automatic stiffness modulation control scheme intended to improve balance control.

Each participant will then be randomized to wear their fixed stiffness prosthesis or the automatic stiffness prosthesis. Subjects will be fit with the IMU sensors on their ankles, wrists, and upper torso. The automatic stiffness prosthesis will be programmed to emulate the user-specific and activity-specific automatic stiffness modulation control scheme. Subjects will be provided at least 10 minutes to walk about the laboratory to learn how the study prosthesis performs. Subjects, wearing the study prosthesis (fixed or automatic stiffness), will then walk a defined course about the hospital facility (both indoors and outdoors) in which each of the laboratory-based ambulatory activities will be represented. A study investigator will accompany the subject at a following distance of ~5 meters while video recording their gait. After completing the defined course, the subject will return to the laboratory where they will complete the Prosthetic Limb Users Survey of Mobility and the Activities-Specific Balance Confidence Scale questionnaires to assess their perceived functional mobility and balance confidence. The subject will then don the other study prosthesis (fixed or automatic stiffness) and then repeat the walk about the defined course and complete the two questionnaires a second time.

The results of this experiment will determine if automatic stiffness modulation improves the balance control of those with lower-limb amputation as they perform typical ambulatory activities of daily living using both biomechanical analyses and self-report assessments of perceived functional mobility and balance confidence.

The investigators hypothesize that the automatic stiffness prosthesis will provide improved balance control in real-world environments compared to the user's fixed stiffness prosthesis that was clinically prescribed. The investigators further hypothesize that the Prosthetic Limb Users Survey of Mobility score reported after wearing the automatic stiffness prosthesis will be greater than the score reported after wearing the fixed stiffness prosthesis, and the Activities-Specific Balance Confidence Scale score reported after wearing the automatic stiffness prosthesis will be greater than the score reported after wearing the fixed stiffness prosthesis.

• Study Type: Interventional
• Enrollment (Estimated): 20
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Washington
    • Seattle, Washington, United States, 98108
      • VA Puget Sound Healthcare System
      • Principal Investigator: Glenn K Klute, PhD
      • Contact: Glenn K Klute, PhD; Phone Number: 206.277.6792; Email: Glenn.Klute@va.gov
      • Contact: Elise Campbell; Phone Number: 206.277.6792; Email: Elise.Campbell@va.gov
      • Principal Investigator: Richard R Neptune, PhD

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Unilateral transtibial (below-knee) amputation
• Been fit with a prosthesis and used it for at least 6 months
• Wear the prosthesis for 4 or more hours on average per day
• Be at least one-year post-amputation
• Able to walk on a treadmill

Exclusion Criteria:

• Presence of disorder, pain, or injury other than amputation that interferes with gait
• Current skin irritation or injury on residual limb
• Use of an assistive device for walking (cane, walker, etc.)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Crossover Assignment
• Masking: Double

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Fixed stiffness prosthesis then automatic stiffness prosthesis; A within-subject crossover experiment will be conducted to determine if differences in balance control (peak-to-peak range of frontal plane whole body angular momentum) exist between two study prostheses. The two study prostheses include (1) the participant's fixed stiffness prosthesis and (2) a novel, automatic stiffness prosthesis. The order in which participants wore the study prostheses was randomized. The study will be conducted over 2 weeks. All participants will walk a defined course (both indoors and outdoors) about a hospital facility. Participants in this group will wear their fixed stiffness prosthesis first and then the automatic stiffness prosthesis.	Device: Fixed stiffness prosthesis; The participant's clinically prescribed prosthesis whose stiffness category is determined by the person's body weight and activity level (standard clinical practice).; Device: Automatic stiffness prosthesis; A novel prosthesis whose user-specific and activity-specific stiffness profile is automatically modulated based on their ambulatory activity.
Experimental: Automatic stiffness prosthesis then fixed stiffness prosthesis; A within-subject crossover experiment will be conducted to determine if differences in balance control (peak-to-peak range of frontal plane whole body angular momentum) exist between two study prostheses. The two study prostheses include (1) the participant's fixed stiffness prosthesis and (2) a novel, automatic stiffness prosthesis. The order in which participants wore the study prostheses was randomized. The study will be conducted over 2 weeks. All participants will walk a defined course (both indoors and outdoors) about a hospital facility. Participants in this group will wear the automatic stiffness prosthesis and then their fixed stiffness prosthesis.	Device: Fixed stiffness prosthesis; The participant's clinically prescribed prosthesis whose stiffness category is determined by the person's body weight and activity level (standard clinical practice).; Device: Automatic stiffness prosthesis; A novel prosthesis whose user-specific and activity-specific stiffness profile is automatically modulated based on their ambulatory activity.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Peak-to-peak range of the frontal plane whole-body angular momentum	Frontal plane whole-body angular momentum is a measure of the extent to which a person will rotate in the frontal plane in the absence of an external force or torque. The peak-to-peak range quantifies how much this metric varies and is used to describe a person's balance.	During study visit (approximately 3 hours)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Prosthetic Limb Users Survey of Mobility	The Prosthetic Limb Users Survey of Mobility is a self-report instrument designed to measure the mobility of adults with lower limb amputations, utilizing a set of calibrated questions to assess perceived mobility in various activities. The Prosthetic Limb Users Survey of Mobility has been recommended by the National Institute of Child Health and Human Development as a core Common Data Element for lower-limb loss research as outcome measures to assess mobility.	During study visit (approximately 3 hours)
Activities-Specific Balance Confidence Scale	The Activities-Specific Balance Confidence Scale is a 16-item self-report questionnaire that measures an individual's confidence in performing daily activities without losing balance or feeling unsteady. It is widely used to identify individuals at risk of falls and to guide interventions aimed at improving balance and mobility. The Activities-Specific Balance Confidence Scale has been recommended by National Institute of Child Health and Human Development as a core Common Data Element for lower-limb loss research as an outcome measure to assess balance.	During study visit (approximately 3 hours)

Collaborators and Investigators

• Sponsor: Seattle Institute for Biomedical and Clinical Research
• Collaborators: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)

Study record dates

Study Major Dates

• Study Start (Estimated): November 1, 2026
• Primary Completion (Estimated): November 1, 2027
• Study Completion (Estimated): November 1, 2028

Study Registration Dates

• First Submitted: August 10, 2026
• First Submitted That Met QC Criteria: August 25, 2026
• First Posted (Actual): August 28, 2026

Study Record Updates

• Last Update Posted (Actual): August 28, 2026
• Last Update Submitted That Met QC Criteria: August 25, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Keywords: gait; biomechanics; below knee amputation; lower limb prosthesis; transtibial amputation
• Other Study ID Numbers: 1817327-27; 1R01HD111514-01A1 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified data sets of all individual participant data collected throughout the trial will be made available, in machine-readable format, on the Eunice Kennedy Shriver National Institute of Child Health and Human Development Data and Specimen Hub. The de-identification procedures will follow 164.514(a) of the Health Insurance Portability and Accountability Act Privacy Rule.
• IPD Sharing Time Frame: Publication-associated datasets will be submitted to Data and Specimen Hub at least 4 months prior to publication so that data can be shared on or before the initial publication date. The full study dataset will be submitted to Data and Specimen Hub at least 6 months prior to the end of the award period. The Data and Specimen Hub do not currently have any data deprecation or sunsetting protocols, allowing shared data to be preserved for the foreseeable future.
• IPD Sharing Access Criteria: The Data and Specimen Hub are a National Institutes of Health controlled-access data repository. The Eunice Kennedy Shriver National Institute of Child Health and Human Development Data and Specimen Hub Data Access Committee reviews all requests to access Data and Specimen Hub data from identity-verified requesters to determine whether the proposed use is scientifically and ethically appropriate and does not conflict with constraints or research data use limitations identified by the institutions that submitted the research data. The Recipient's institution and the Recipient must sign and agree to the terms and conditions in the N Eunice Kennedy Shriver National Institute of Child Health and Human Development Data and Specimen Hub Data Use Agreement for accessing research data.
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; ICF

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: Yes
• product manufactured in and exported from the U.S.: No