Agonist-Antagonist Myoneural Interface for Functional Limb Restoration After Transtibial Amputation

BACKGROUND:

Loss of limb profoundly impacts a person's health, productivity, independence, and quality of life. However, state-of-the-art medical and prosthesis technologies fall short of offering seamless human-device communication to those who require limb amputation. Ongoing, interactive efforts to advance amputation surgery techniques and develop novel "bionic" prostheses and prosthetic control systems are underway in an effort to address this interfacing challenge and thereby improve clinical outcomes within the population of amputees. We recently reported on the results of a first-in-human trial in which a prototype bionic prosthesis was tested in a recipient of a modified transtibial amputation. The modified amputation procedure involved the surgical construction of agonist-antagonist myoneural interfaces (AMIs) within the residual limb, where each AMI comprised two muscles - an agonist and an antagonist - connected in series. To enable the force produced by one muscle to cause stretch of its partner, "pulleys" were also constructed from the medial and lateral tarsal tunnels, including segments of each tunnel's native tendons, that were procured from the distal amputated limb and affixed to the residual limb tibia. The two AMIs were constructed via coaptation of the tibialis anterior and lateral gastrocnemius muscles to either end of the tendon portion passing through the proximally positioned tarsal tunnel, and coaptation of the tibialis posterior and peroneus longus muscles to either end of the tendon passing through the distally positioned tunnel. Following rehabilitation, this first recipient of the "AMI transtibial amputation" tested the feasibility of using his surgically constructed AMIs to control a prototype bionic prosthesis. The bionic prosthesis allowed motion in two degrees of freedom through independent actuation of powered ankle and subtalar joints, and the control algorithm allowed electromyography (EMG)-modulated control over prosthetic joint position and joint impedance.

Functional testing involved linking the proximal and distal AMIs within the participant's residual limb to the prosthetic ankle and subtalar joints through the use of surface EMG electrodes, intramuscular fine-wire electrodes, and functional electrical stimulation. The results of performance testing in this first AMI recipient suggested that AMIs can provide a biological tissue interface that can potentially offer a person with an amputation intuitive motor control of the affected limb and a bionic prosthesis while also enabling proprioception. The unique biomimetic tissue architecture of the AMI recapitulates a dynamic, mechanically functional muscle-tendon-muscle linkage that inherently provides mechanoreceptive biological sensors. Consequently, the AMI tissue architecture inherently preserves natural, bi-directional communication between surgically reconstructed limb musculature and the central nervous system, thereby building on and offering advantages over previously described neural interfacing approaches such as targeted muscle reinnervation (TMR), regenerative peripheral nerve interfaces (RPNIs), and peripheral nerve interfaces. Additionally, the surgical design implemented in the AMI transtibial amputation preserves the native innervation and vascularization for each nerve and muscle component, thereby offering a more robust, viable surgical construction than either TMR or RPNI, which instead rely upon the less robust regenerative processes of reinnervation and revascularization for long term viability. Long term functionality of the AMI is facilitated by the incorporation of autologous tarsal tendon and tunnel components, eliminating the need for either allogeneic grafts or synthetic implant materials. By providing a platform for robust efferent decoding of movement intent, as well as usable afferent feedback from a prosthetic joint, the AMI transtibial amputation paradigm has the potential to reinstate the human central nervous system as the primary mediator of prosthetic joint control.

STUDY OVERVIEW:

The goal of this clinical trial is to evaluate the efficacy of the AMI transtibial amputation.