Pivot-Flex Foot: Optimal Coupling Ratio Between Transverse and Sagittal-plane Motions Using a Torsionally Adaptive Prosthesis for Individuals With Lower Limb Amputation

Pivot-Flex Foot: Torsionally Adaptive Prosthesis for Individuals With Lower Limb Amputation

When prescribing a prosthetic foot, clinicians face a dizzying array of choices as more than 200 different prosthetic feet are available. While these conventional prosthetic feet primarily function in the sagittal plane, the intact foot and ankle comprise a complex set of joints that allow rotation in multiple planes of motion. Some of these motions are coupled, meaning rotation in one plane induces motion in another. One such coupling is between the sagittal and transverse planes. For every step, plantar- and dorsi-flexion motion in the sagittal plane is coupled with external and internal rotation of the shank relative to the foot in the transverse plane. There is no prosthetic foot available for prescription that mimics this natural coupling.

To investigate the need for this coupling, the investigators have built a torsionally adaptive prosthesis where the coupling ratio between the transverse- and sagittal-planes can be independently controlled with a motor.

This research has one specific aim: to identify the optimal coupling ratio between transverse- and sagittal-plane motions using a novel, torsionally adaptive prosthesis for individuals with lower limb amputation. The investigators will conduct a human subject experiment wearing the motor-driven and computer controlled torsionally adaptive prosthesis. Individuals with lower limb amputation will be asked to walk in a straight line and in both directions around a circle while the coupling ratio between transverse- and sagittal-plane motions is varied between trials. Participants will be blinded to the coupling ratio.

The investigators hypothesize that: (1) a coupling ratio exists that minimizes undesirable transverse-plane socket torque and (2) there will be a coupling ratio that individuals with lower limb amputation prefer.

Study Overview

• Status: Completed
• Conditions: Lower Extremity Amputation
• Intervention / Treatment: Device: Torsionally adaptive prosthesis with 0:1 coupling ratio; Device: Torsionally adaptive prosthesis with 1:6 coupling ratio; Device: Torsionally adaptive prosthesis with 1:4 coupling ratio; Device: Torsionally adaptive prosthesis with 1:3 coupling ratio; Device: Torsionally adaptive prosthesis with 1:2 coupling ratio

Detailed Description

The human ankle is a complex mechanism that does not behave like a simple hinge. Instead, rotations in all three axes are allowed and some are coupled together. In particular, the axis of rotation of the talo-crural joint during ankle flexion is inclined downwards and laterally relative to horizontal, and the rotation ranges from 10 to 26 degrees among individuals. This rotation couples plantar- and dorsi-flexion motion with external and internal rotation of the shank relative to the foot, respectively. This feature of the natural limb has not been replicated in prosthetic feet and ankles.

Lower limb amputees take thousands of steps on their prosthesis each day and none feature coupled motion between the transverse- and sagittal-planes. The absence of this natural coupling may be related to the high incidence of residual limb soft tissue injuries, the need for compensatory gait, and overall dissatisfaction with their prostheses.

Transverse rotation adapters, consisting of simple torsional springs, are available for prescription. These devices can increase transverse-plane rotations and decrease transverse-plane torques, but their use is not widespread and if excessively compliant, may reduce gait stability. Cost, weight, prosthesis build height, and the inability for the user to adjust the stiffness may all play a role in their lack of adoption, but it may also be that the transverse-plane rotation is not coupled with the sagittal-plane. With these devices, motion only occurs in the transverse-plane when a transverse-plane torque is applied.

This research has one specific aim: to identify the optimal coupling ratio between transverse- and sagittal-plane motions using a novel, torsionally adaptive prosthesis for individuals with lower limb amputation. The investigators will fit a sample population of unilateral transtibial amputees with the motor-driven and computer controlled torsionally adaptive prosthesis.

Participants perform three activities: walking in a straight line (study visit 1) and in both directions around a circle (study visit 2). During each of these three activities, the torsionally adaptive prosthesis will be set to five different coupling ratios in random order. Participants will be blinded to the coupling ratio.

The general hypotheses for this study are: (H1) a coupling ratio exists between 0 (no coupling) to 1:2 (one degree of transverse-plane motion for every two degrees of sagittal-plane motion) that minimizes transverse-plane socket torque and (H2) an amputee preferred coupling ratio will exist within this range.

This research will discover how best to couple transverse- and sagittal-plane motion in the prostheses of lower limb amputees.

• Study Type: Interventional
• Enrollment (Actual): 14
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Washington
    • Seattle, Washington, United States, 98108-1532
      • VA Puget Sound Health Care System Seattle Division, Seattle, WA

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 18 years to 70 years (Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Unilateral transtibial amputation
• Been fit with a prosthesis and used it for at least six months
• Wear the prosthesis for four or more hours on an average day
• Prescribed prosthesis can accommodate fitment of the study prosthetic components to be tested (determined at initial visit)

Exclusion Criteria:

• Improper fit and suspension with current prosthesis and one cannot be achieved with clinical resources (determined at initial visit)
• Current skin irritation or injury on residual limb
• Osteoarthritis, injury, or pain that interferes with walking ability
• Currently incarcerated
• Pregnant (determined via self-report)
• Inadequate cognitive function or language proficiency to consent to participate

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Factorial Assignment
• Masking: None (Open Label)

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Straight line walking; All participants will walk in a straight line while wearing the study prosthesis.	Device: Torsionally adaptive prosthesis with 0:1 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 0:1 means there will be no coupling between the transverse- and sagittal-plane motion. That is, regardless of any motion in the sagittal plane, there will be zero motion in the transverse plane.; Device: Torsionally adaptive prosthesis with 1:6 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:6 means there will be one degree of motion in the transverse plane for every six degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:4 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:4 means there will be one degree of motion in the transverse plane for every four degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:3 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:3 means there will be one degree of motion in the transverse plane for every three degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:2 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:2 means there will be one degree of motion in the transverse plane for every two degrees of motion in the sagittal plane.
Experimental: Circle walking with prosthesis inside; All participants will walk around a 1-meter radius circle with their prosthesis on the inside of the circle.	Device: Torsionally adaptive prosthesis with 0:1 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 0:1 means there will be no coupling between the transverse- and sagittal-plane motion. That is, regardless of any motion in the sagittal plane, there will be zero motion in the transverse plane.; Device: Torsionally adaptive prosthesis with 1:6 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:6 means there will be one degree of motion in the transverse plane for every six degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:4 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:4 means there will be one degree of motion in the transverse plane for every four degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:3 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:3 means there will be one degree of motion in the transverse plane for every three degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:2 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:2 means there will be one degree of motion in the transverse plane for every two degrees of motion in the sagittal plane.
Experimental: Circle walking with prosthesis outside; All participants will walk around a 1-meter radius circle with their prosthesis on the outside of the circle.	Device: Torsionally adaptive prosthesis with 0:1 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 0:1 means there will be no coupling between the transverse- and sagittal-plane motion. That is, regardless of any motion in the sagittal plane, there will be zero motion in the transverse plane.; Device: Torsionally adaptive prosthesis with 1:6 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:6 means there will be one degree of motion in the transverse plane for every six degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:4 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:4 means there will be one degree of motion in the transverse plane for every four degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:3 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:3 means there will be one degree of motion in the transverse plane for every three degrees of motion in the sagittal plane.; Device: Torsionally adaptive prosthesis with 1:2 coupling ratio; The torsionally adaptive prosthesis can be programmed to couple the motion between the transverse- and sagittal-planes. A coupling ratio (transverse:sagittal) of 1:2 means there will be one degree of motion in the transverse plane for every two degrees of motion in the sagittal plane.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Peak Transverse-plane Prosthetic Socket Torque Normalized to Body Mass	Peak transverse-plane prosthetic socket torque measured while walking normalized to body mass	During walking trials for each coupling ratio

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Satisfaction With the Prosthesis	An 11-point Likert scale will be used to record the subject's perception of satisfaction with the prosthesis after completing the trials for each coupling ratio. Participants will be asked to rate their satisfaction with the prosthesis on a 0 - 10 scale. Zero represented the most uncomfortable socket fit the subject could imagine, and ten represented the most comfortable socket fit.	Immediately following walking trials for each coupling ratio

Collaborators and Investigators

• Sponsor: VA Office of Research and Development
• Investigators: Principal Investigator: Glenn K Klute, PhD, VA Puget Sound Health Care System Seattle Division, Seattle, WA

Study record dates

Study Major Dates

• Study Start (Actual): April 18, 2018
• Primary Completion (Actual): October 1, 2024
• Study Completion (Actual): November 18, 2024

Study Registration Dates

• First Submitted: May 9, 2018
• First Submitted That Met QC Criteria: May 9, 2018
• First Posted (Actual): May 22, 2018

Study Record Updates

• Last Update Posted (Estimated): November 19, 2025
• Last Update Submitted That Met QC Criteria: November 5, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: gait; biomechanics; below knee amputation; lower limb prosthesis; transtibial amputation
• Other Study ID Numbers: A2456-R; RX002456 Part 1 (Other Identifier: Department of Veterans Affairs, Rehabilitation R&D); I01RX002456-01A1 (U.S. NIH Grant/Contract)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: A de-identified, anonymized dataset in machine-readable format will be created and shared for all individual participant data (IPD) that underlie results in a publication. The investigators will follow 164.514(a) of the HIPAA Privacy Rule for de-identification of IPD.
• IPD Sharing Time Frame: Within six months after publication of final study findings.
• IPD Sharing Access Criteria: Open access through PubMed Central, SimTK, PhysioNet, or other similar open-source data repository websites. The investigators will work with manuscript publishers when possible to link the final study data sets to an appendix of supplemental materials on the publisher websites.

Drug and device information, study documents

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