In a first for the field of upper limb prosthetics, a pioneering surgical technique has allowed an amputee to attach a Modular Prosthetic Limb (MPL) developed by researchers at the Johns Hopkins University Applied Physics Laboratory (APL) directly to his residual limb, which has enabled a greater range of motion and comfort than previously possible.

Fig.1 - A pioneering surgical technique has allowed an amputee to attach APL’s Modular Prosthetic Limb directly to his residual limb, enabling a greater range of motion and comfort than previously possible. (Credit: JHU APL)
According to Michael McLoughlin, Chief Engineer in APL’s Research and Exploratory Development Department, “This accomplishment has eliminated one of the biggest gaps in prosthetic development: the socket.”

The socket, which is the part of the prosthesis that attaches to the body, is the most critical component of a prosthesis. When it doesn’t fit correctly, the patient can experience pain, sores, and blisters, and the prosthesis will feel heavy and cumbersome, said APL’s Courtney Moran, a clinical prosthetist who works closely with patients. Even with well-designed sockets, patients have reported problems with heat, sweating, and chafing, she explained.

Johnny Matheny is one of several patients who has worked with the MPL over the years to help scientists, engineers, and physicians fine-tune its capabilities and test its usability. His left arm was amputated in 2008 because of cancer, and because of his willingness to work with researchers, he is considered a pioneer of advanced arm prosthetics.

Matheny was the first patient at the Johns Hopkins Hospital to undergo targeted muscle reinnervation (TMR), a surgical procedure that reassigns nerves that once controlled the arm or hand, which can make it possible for upperextremity amputees to better use and control an advanced prosthetic device. In addition to the MPL, he has also testdriven some of the most advanced, state-of-the-art prosthetic arms in the world. When introduced to the idea of undergoing a surgery that would allow him to mount the prosthetic arm directly to his residual limb, he jumped at the chance.

How It Works

The procedure is called osseointegration. First, a threaded titanium implant, called a fixture, is inserted into the marrow space of the bone of the residual limb. Over time, the fixture becomes part of the bone. Then, several weeks after the first surgery, a titanium extension, known as an abutment, is attached to the fixture and brought out through the soft tissues and skin. The prosthesis can then be directly attached to the abutment.

Richard McGough, chief of the Division of Musculoskeletal Oncology at the University of Pittsburgh Medical Center, performed the stage one surgery on Matheny in March 2015 and stage two in June 2015, making Matheny the first patient in the US to receive the TMR and osseointegration. Four months later, Matheny traveled to APL and attached the MPL directly to his body for the first time.

A Natural Fit

Matheny described an almost immediate transformation in his ability to control the MPL. “Before, the only way I could put the prosthetic on was by this harness with suction and straps,” he said, “but now, with osseointegration, the implant does away with all that. It’s all natural now. Nothing is holding me down. Before, I had limited range; I couldn’t reach over my head and behind my back. Now, boom! That limitation is gone.”

Over the course of three days, Matheny went through a series of exercises in APL’s prosthetics laboratory to determine the limits of his newfound control and range of motion. Because Matheny had configured a weighted attachment for the implant that was about three pounds, and had been doing exercises on his own with this weighted implant, he was immediately able to put the technology into practice. He was able to demonstrate individual finger control, simultaneous finger control, two degrees of freedom at the wrist, multiple grasps, and worked through simulated activities of daily living. (See Figure 1)

McLoughlin said: “The challenge for us next is to really figure out how to get this technology out of the laboratory and into the hands of people who need it. For all the incredible things that we see Johnny doing with the MPL, when we’re finished here in the lab he has to leave it here and go home. We really want to enable him to leave with that arm and to use it every day. And that’s what Johnny wants, too.”

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