Soldiers who have been injured in war are getting steps closer — or in this case, perhaps, arms' length closer — to a prosthetic upper limb with what researchers call eight degrees of freedom and offering the additional feature of sensory feedback, both features approaching the natural activity and feel of the natural human arm.

The Johns Hopkins University's Applied Physics Laboratory (APL; Laurel, Maryland), a research team developing this technology, said that the prototype of this new prosthetic arm, called Proto 1 — and, hopefully, ultimately commercialized by a medical device maker — offers a level of control far beyond the current state-of-the-art.

The Proto 1 prototype has been developed in the first two-year phase of a four-year program called Revolutionizing Prosthetics. The work is being conducted at the non-profit APL through a contract with Defense Advanced Research Projects Agency (DARPA; Fort Detrick, Maryland).

John Bigelow, assistant program manager for the Revolutionizing Prosthetics 2009 program, told Medical Device Daily that the development of prosthetic arms has lagged far behind comparable work for those who have lost legs.

"[T]here is and has been a fair amount of progress on the lower limb, and that's because it's a far more common occurrence — and it's also a much simpler problem" — simpler because arms and hand movements are much more varied that those of the leg and foot. Thus, prosthetic leg R&D has made strong progress, he said, "whereas the upper extremity arena really has not been addressed at all."

That situation is obviously now changing, through the collaboration of at least eight entities. Among these are Otto Bock (Vienna, Austria), which was responsible for the design and fabrication of mechanical subsystems for Proto 1; the University of Southern California (Los Angeles), which provided the collaborative development of the virtual patient training and clinical interface system; and the Rehabilitation Institute of Chicago (RIC; Chicago), which provided the mechanical components of Proto 1 designed by Richard Weir.

Between late July and early August, APL expects to unveil a second prototype which will have even more movement, described as "25 degrees of freedom." Ultimately, by at least 2009, Bigelow said, APL wants to have a neural interface with an arm, whereby the brain is essentially controlling its movement by acquiring the signals in the brain, with those signals then "naturally" controlling the prosthetic.

"The end objective of a four-year program is 22-plus degrees of freedom, if you can imagine full dexterity in the hand," Bigelow said. "But to control that many degrees of freedom, we need much more robust access to control signals and signal analysis techniques."

The movement achieved by Proto 1 — offering what the researchers call an "advanced degree" of natural control and integrated sensory feedback — is enabled by a technology called Targeted Muscle Reinnervation (TMR), a technique pioneered by Dr. Todd Kuiken at RIC that involves the transfer of residual nerves from an amputated limb to unused muscle regions in proximity to the injury.

For Proto 1, the nerves were transferred to the pectoral area of the patient's chest. That procedure is designed to provide a "more intuitive use" of the prosthetic arm and allows for the "natural sensations of grip strength and touch," APL said.

But in the full context of the program, the TMR technology provides only a first step, Bigelow told MDD.

"Our objective is to take that much farther and through other advanced devices such as injectable myoelectric sensors [IMES] that go through the muscle; implantable peripheral nerve sensors that can pick up directly peripheral nerve signals; and even doing some research brain integration techniques, if you will," he said.

In late summer, a second prototype will be revealed.

"There is still significant work to be done to determine how best to control this number of degrees of freedom and ultimately how to incorporate sensory feedback based on these sensory inputs within the human nervous system," said APL's Stuart Harshbarger, who leads the Revolutionizing Prosthetics Program. "The APL team is already driving a virtual model of Proto 2 with data recorded during the clinical evaluation of Proto 1, and the team is working to identify a robust set of grasps that can be controlled by a second patient later this year."

Another development accomplished during testing of Proto 1 was the functional demonstration of IMES, very small devices that are injectable or surgically implantable, used to measure muscle activity at the source vs. surface electrodes on the skin that were used during testing of the first prototype.

"The IMES devices, coupled with the TMR procedures, promise to increase the fidelity of control and can be used in certain injury scenarios to provide a significant improvement on their own merit," Harshbarger said.

The goal is to have the fully developed prosthetic arm ready for clinical trials by the end of 2009; however, APL is required to go through the FDA's regulatory channels to prepare whatever the next step is for conducting the clinical trials on the final device to result from the Revolutionizing Prosthetics program.

Among the candidates for executing the clinical trials are RIC or "possibly the VA, since [the project] is targeted at war fighters," Bigelow said.

Bigelow noted that returning veterans are "really the driving force behind the program."

"They've given so much, and our objective is to restore some level of quality-of-life," he said.