The Ewing Amputation: The First Human Implementation of the Agonist-Antagonist Myoneural Interface
Matthew J. Carty, MD1; Tyler R Clites, PhD2; Hugh Herr, PhD3; Shriya S Srinivasan, BS3; Anthony N Zorzos, PhD2
1Division of Plastic Surgery, Brigham and Women's Hospital, Boston, MA, 2MIT, Cambridge, MA, 3Massachusetts Institute of Technology, Cambridge, MA
Background: The agonist-antagonist myoneural interface (AMI) comprises a surgical construct and a neural control architecture designed to serve as a bidirectional interface for closed-loop control of advanced limb prostheses, capable of providing proprioceptive sensation of prosthetic joint position, speed and torque to the central nervous system. The AMI is constructed via mechanical linkage of biological agonist and antagonist muscles, thereby providing a dynamic alternative to the isometric handling of residual limb musculature in a standard amputation. The AMI surgical procedure has previously been vetted in murine and caprine models; we here present the surgical results of its translation to human subjects.
Methods: Modified unilateral below knee amputations (BKAs) were performed in the elective setting in three human subjects between July 2016 and April 2017. AMIs were constructed in each subject to preserve the dynamic agonist-antagonist muscle relationships that drive control and proprioception of both the ankle (tibialis anterior and lateral/medial gastrocnemius linkage) and subtalar (peroneus longus and tibialis posterior) joints. Intraoperative, perioperative, and postoperative residual-limb outcome measures were recorded and analyzed, including electromyographic and radiographic imaging of AMI musculature, and subjective outcome measures of proprioceptive position sensations.
Results: The mean subject age was 38 ± 13 years, and mean BMI was 29.5 ± 5.5 kg/m2. All subjects were male, and all were left-sided amputations. The indications for amputation included rock climbing fall, IED injury, and congenital abnormality. Mean operative time was 346 ± 87 minutes, including 120 minutes of tourniquet time per subject. Average length of stay was 4.7 ± 1.2 days. All patients participated in a modified rehabilitation regimen beginning four weeks following surgery. Complications were minor and included transient cellulitis and one instance of delayed wound healing. All subjects demonstrated mild limb hypertrophy postoperatively. All patients demonstrated intact construct excursion with volitional muscle activation, as evidenced by radiographic imaging and electromyography. All patients reported a high degree of phantom limb position perception with no reports of phantom pain.
Conclusions: The AMI is a novel peripheral neural interface to an external limb prosthesis that offers the possibility of improved prosthetic control and restoration of muscle-tendon proprioception. Our initial results in this first cohort of human patients are promising and provide evidence as to the potential role of AMIs in the care of patients requiring below knee amputation.
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