Since the first of the new amputation procedures was performed in 2016, 30 patients have had the surgery performed on one or both legs — including U.S. Paralympian Morgan Stickney, a double amputee who just won two swimming gold medals in Tokyo. Their results show that Majetich’s experience is not uncommon.
“What we’ve found are a number of distinct advantages of the AMI amputation,” said Hugh Herr, an MIT Media Lab professor, using the shorthand for the procedure he jointly developed with Carty. (AMI stands for agonist-antagonist myoneural interface, which refers to the joining of opposing, agonist and antagonist, muscles.) Herr said the AMI patients have felt less pain in their residual limbs, and their limbs don’t atrophy, as is typical after a standard amputation, resulting in a poor fit and pain when using a prosthesis.
In a study published last December, MIT postdoctoral fellow Shriya Srinivasan and colleagues in Herr’s group reported that when AMI patients moved their phantom ankle, a part of the brain associated with proprioception lit up on functional MRI scans just as much as it did in patients with intact limbs. This suggests the surgery fully restored patients’ ability to sense their limbs’ position and motion, a result Herr called “truly remarkable.” In people who had standard amputations, activation of this region was significantly reduced.