Edited by Andrea Timpano

The Reconstructive Surgery

It’s not every day that scribbling on a napkin leads to a major medical breakthrough. But that’s precisely the outcome Matthew Carty and Hugh Herr set in motion while dining (and doodling) at a Boston restaurant some 10 years ago.

It was then that the pair—Carty, a specialist in reconstructive surgery at Brigham and Women’s Faulkner Hospital, and Herr, an MIT professor and acclaimed prosthetics inventor—laid the groundwork for a promising amputation procedure known as the AMI, short for the Agonist-Antagonist Myoneural Interface. In a traditional amputation, the link between the limb’s muscles—which normally work together—is severed, as is the brain’s ability to communicate with them. With an assist from those early napkin drawings and future brainstorming sessions, Carty and Herr ultimately realized they could potentially repair those connections by using matter from the amputated limb to recouple the muscles. If successful, the procedure could (among other benefits) reduce what’s known as “phantom pain” in the missing limb, while also better equipping the remaining appendage for advanced
prosthetics—very good news, considering an estimated 185,000 Americans undergo amputation procedures each year. “The design principles were already present in the body,” Carty says. “All we had to do was figure out how to operationalize the idea.”

They did. After researchers successfully tested the theory in animals and, later, on human cadavers, the first AMI procedure—a below-the-knee amputation—was performed on a live patient in 2016. Since then, 37 AMI surgeries have been completed, thanks in no small part to the ongoing efforts of Carty’s and Herr’s teams, plus collaborators at Walter Reed National Military Medical Center. While the first implementations of the AMI procedure were performed in above- and below-knee amputations, the technique can now be utilized in above- and below-elbow operations. Patients who’ve undergone traditional amputation surgeries are eligible for the procedure, too. “It continues to be more successful than I ever thought it would be,” Carty says.

Of course, there’s still more work to be done. As prosthetic technology continues to evolve, so too will the surgery to ensure alignment. And despite the growing number of success stories, Carty says it could take years for the AMI procedure—which is still being refined and standardized—to be accepted as common practice. “We know from past experience that the adoption curve for new techniques in surgery is about 20 years,” he says. Even so, Carty remains hopeful. “If we can move the needle a little bit for the benefit of these patients, that’s why we’re all here,” he says. —A.T.