An Alternative Surgical Architecture to Broaden Accessibility of the Agonist-antagonist Myoneural Interface (AMI)
Tyler R Clites, PhD1; Matthew J. Carty, MD2; Shriya S Srinivasan, BS1; Hugh Herr, PhD1;
1Massachusetts Institute of Technology, Cambridge, MA, 2Division of Plastic Surgery, Brigham and Women's Hospital, Boston, MA
The Agonist-antagonist Myoneural Interface (AMI) is a method to enable bi-directional neural communication of proprioceptive information from a prosthetic limb to the central nervous system. An AMI is comprised of two muscles - an agonist and an antagonist - surgically connected in series within an amputated residuum, such that the dynamic muscle relationships that exist within native anatomy are preserved. This mechanical coupling enables mechanoreceptors within both muscles to communicate proprioceptive information to the central nervous system. At present, the AMI has been implemented at the transtibial level in nine human patients. The surgical architecture used in these patients leverages "spare parts" from the amputated limb to create sliding surfaces for transduction of force from one muscle to another. In the present study we evaluate alternative surgical constructions of the AMI that are not dependent on the availability of distal tissues.
Figure 1: One AMI was surgically constructed in the residual limb of a goat at the time of primary transtibial amputation. An Alloderm pulley enabled coupled motion of the AMI muscles.
Materials and Methods
One AMI was surgically created at the time of primary transtibial amputation in the residual limb of a goat. Distal ends of the lateral gastrocnemius and tibialis cranialis were coapted across an Alloderm "pulley" to create an agonist-antagonist muscle pair. The residual musculature was sensorized with implantable epimysial and intramuscular electrodes, as well as sonomicrometry crystals. Electromyography and muscle-state measurements were chronically recorded from the residuum while the animal ambulated without a prosthesis, and fluoroscopic evaluations of coupled motion in the presence of artificial muscle stimulation were carried out under anesthesia. The animal was then sacrificed, and the residuum was examined.
Muscle-state measurements and fluoroscopic evaluations show coupled motion of the agonist-antagonist pair in the presence of both natural neural commands and artificial muscle stimulation. Post-mortem examination of the residual tissues showed no signs of necrosis and no abundance of scarring.
These findings indicate that an alternative AMI surgical architecture is able to provide coupled motion of agonist-antagonist muscle pairs. This new architecture has the potential to broaden the patient population that would benefit from the AMI to include those with limited availability of distal tissues.
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