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School of Medicine
The Cutting Edge - A Quest for an Arm Turns Wondrous
Cutting Edge Fall 2012
A Quest for an Arm Turns Wondrous
Date: December 4, 2012
Aided by biomedical engineer Robert Armiger, Johnny Matheny practices tactile motions with his advanced prosthetic arm.
When he lost his arm to cancer in 2008, Johnny Matheny accepted his new reality and forged ahead. Hoping to turn a negative into a positive, the 57-year-old West Virginia resident began exploring prosthetic options. With so many soldiers returning home from overseas, Matheny reasoned, technology surely had advanced to help those who’d lost limbs in combat.
The possibilities, however, turned out to be overwhelming.
In his quest for the finest prosthetic arm, Matheny eventually wound up at The Johns Hopkins Hospital, in the care of trauma surgeon Albert Chi, who has a longstanding interest in biomedical engineering and technology, valuing its potential for improving patients’ quality of life. Chi and Matheny turned out to be a perfect match. Not only was Chi experienced with a technique known as targeted innervations—by which nerves can be rerouted through spare muscle so that amputees can operate motorized prosthetics using motor commands—but he was also aware of just such a prosthetic limb.
Matheny, meanwhile, was an ideal patient, and not only because of his eagerness and compliance. During the operation to remove his arm, his surgeon—based in Pittsburgh—had anticipated that Matheny might one day have access to better prosthetic technology and had been careful to leave his nerve endings intact and long enough so that they could still be accessible should a technologically advanced arm come on the market. As a result, Matheny was a prime candidate for Chi’s reinnervation procedure. Immediately after the surgery in November 2011, Matheny recalls Chi’s excitement: “He said he couldn’t have had a better patient, and that it was too easy—better than in any textbook.”
With the surgery over, there was still work to do. After three years of having no arm, Matheny’s remaining nerves and muscles—though intact and functional—had forgotten how to communicate with and respond to motor commands. So Matheny, Chi and a team of physical therapists and technicians set out to retrain those muscles and nerves to perform much like they had before he lost his arm. Using a series of tests, Chi and his team found that not only had the surgery succeeded, but that Matheny had exceeded their expectations by demonstrating sensation, feeling and movement faster than anyone could have anticipated.
“The body is amazing in terms of its will to return to normal function,” Chi says. “When you have a missing limb, all the information is there, but the body has no way to get it out. So we rerouted the pathway for that information so that it can be expressed.”
But much like the brain needs a mouth to express words, Matheny would need an arm and hand to express movement—something better, more advanced than his current prosthetic arm, which has a hook for gripping, but offers little movement capability.
Enter Johns Hopkins University’s Applied Physics Lab, where a motorized arm with a five-fingered hand that operates much as a human hand does is nearing completion. Matheny had already been able to test a similar arm during a previous stay at Hopkins. At that time, he was connected to the prosthetic so that he could practice tactile motions, such as distinguishing between his index and pinky finger. He’s also had the chance to practice at home using a computer program that helps trigger pattern recognition feedback.
Matheny hopes to have his own arm by the end of the year. The possibility, he says, far outstrips what he first imagined when he began his search. “I knew medicine was advancing at a fast pace,” Matheny says, “but I had no clue that anything like this was available. After the surgery, I started feeling all of these different sensations. It was crazy, but a good crazy.”