Trial Outcomes & Findings for Agonist-Antagonist Myoneural Interface for Functional Limb Restoration After Transtibial Amputation (NCT NCT03913273)

Race and Ethnicity were not collected from any participant.

The stability of joint position control in free space is quantified by the number of the distinct synergy activations (distinct movements) achieved out of a total of four targeted movements of interest: (1) ankle plantar flexion (toe down), (2) dorsiflexion (toe up), (3) subtalar joint eversion (sole of foot outward), and (4) subtalar joint inversion (sole of foot inward). For each movement, the subject is asked attempt the movement while the distinct synergy activation/neural signals are quantified using electromyography (EMG) data. An outcome of 4 indicates that the subject was able to produce distinct activations for each of the 4 targeted movements. An outcome of less than 4 indicates that although a subject attempted the movement, they were not able to successfully produce distinct activations for some portion of the targeted movements.

The economy of motion is computed as the total travel distance through synergy space, normalized by the minimum possible/most direct travel path, to reflect control efficiency. Given this definition, the economy of motion indicates the trajectory straightness of movements that were produced to achieve the target discrete movements. For this study, the movements were ankle plantar-dorsiflexion and subtalar inversion-eversion. An outcome of 100% represents how the two movements together could allow for an economy of the targeted movements in that space, indicating perfect economy of motion. The percentage may decrease if a subject achieves the targeted movements in a less efficient manner. For these movements, the economy of motion was evaluated under increasing time constraints from 2.0 s to 1.5 s, 1 s, 0.8 s, and 0.5 s.

To address the clinical trial aim of determining whether AMIs can improve prosthetic terrain adaptations, we assessed swing phase control during stair descent by measuring the capability of the neuroprosthesis to exhibit prosthetic ankle joint plantar flexion characteristic of stair descent. This metric was defined as the change in ankle joint angle from terminal stance to terminal swing, capturing the user's ability to distinctly control joint angle transitions across gait phases of stair descent. For further details see: H. Song, T.-H. Hsieh, S. H. Yeon, T. Shu, M. Nawrot, C. F. Landis, G. N. Friedman, E. A. Israel, S. Gutierrez-Arango, M. J. Carty, L. E. Freed, H. M. Herr, Continuous neural control of a bionic limb restores biomimetic gait after amputation. Nat Med 30, 2010-2019 (2024).

To address the clinical trial aim of determining whether AMIs can improve prosthetic terrain adaptations, we assessed swing phase control during stair ascent by measuring the capability of the neuroprosthesis to exhibit prosthetic ankle joint dorsiflexion characteristic of stair ascent. This metric was defined as the change in ankle joint angle from terminal stance to terminal swing, capturing the user's ability to distinctly control joint angle transitions across gait phases of stair ascent. For further details see: H. Song, T.-H. Hsieh, S. H. Yeon, T. Shu, M. Nawrot, C. F. Landis, G. N. Friedman, E. A. Israel, S. Gutierrez-Arango, M. J. Carty, L. E. Freed, H. M. Herr, Continuous neural control of a bionic limb restores biomimetic gait after amputation. Nat Med 30, 2010-2019 (2024).

Correlation of Ankle Joint Proprioception was measured by applying functional electrical stimulation (FES) to either the tibialis anterior (TA) or lateral gastrocnemius (LG) and instructing the subject to resist the experienced movement. The level of correlation (R2) for both dorsiflexion and plantarflexion between the applied stimulation current and the subjects perceived joint counter-torque for the intervention subjects was compared to control subjects.

We analyzed the correlation (R2) between agonist contraction and antagonist stretch during dorsi and plantar flexion movements. Muscle fascicle strains were estimated from ultrasound data recorded from the agonist and antagonist muscles (e.g. lateral gastrocnemius (LG) and tibialis anterior (TA) during plantar flexion). Fascicle measurements were generated via optical tracking software. In the AMI subjects, because of the mechanical coupling of the agonist and antagonist muscles within the residual limb, a volitional contraction of the agonist muscle inherently induces a passive stretch in the corresponding antagonist muscle. On the other hand, in the control subjects, because the residual muscles are not coapted, we expected to find limited stretch in the antagonist muscle during agonist contraction. With limited stretch in the antagonist from an agonist contraction, perceived joint movement would be lowered from antagonist stretch afferents.