An even more sophisticated and ruggedized version of the microprocessor knee, the X3, was introduced to these same 36 warriors in the summer of 2012. Programmable in up to five modes by means of Bluetooth® technology, the X3 is lighter than the X2, and it’s also water resistant for up to 10 minutes, allowing the wearer to spend brief intervals in the water. The wearer can switch between these modes by either using a hand-held remote or by bouncing on the toe of the prosthesis a pre-determined number of times.
While not exactly passive, the X2 and X3 achieve strength, stability, and grace through resistance; the hydraulic cylinders store and return energy created in the natural swinging motion of the lower leg, allowing the limb to swing freely or lock completely. The Otto Bock microprocessor knees do not actively move, though that has been an option also available to military amputees and veterans since 2007, when the Power Knee, the first motor-powered prosthesis for above-the-knee amputees, was introduced by both the VHA and the Military Health System.
During his service in Operation Iraqi Freedom in 2007, Col. Gregory Gadson was severely injured by an improvised explosive device, resulting in the amputation of both legs above the knee and severe damage to his right arm. U.S. Army photo
Army Col. Gregory Gadson – who took command of Fort Belvoir, Va., on June 25, 2012 – chose to return to active duty after losing both his legs to a roadside bomb in Iraq in May 2007. Both his legs were amputated above the knee, but a pair of Power Knees restored lost muscle function and enabled him to walk and perform normal daily functions. Among service members and veterans who have lost legs, some prefer the Power Knee, while others – particularly unilateral amputees – find it trickier to use than the more intuitive X2 and X3. Increasingly, patients are able to choose which prosthesis fits their own preferences and lifestyles.
While a sturdy and adaptable knee joint is crucial to restoring function, it would in many cases not be adequate for returning many servicemen and women to active duty. The lower leg – the interaction of the calf, foot muscles, and ankle joint – requires a finer degree of control for tasks such as rising from a chair or descending stairs. In the spring of 2011, several Walter Reed patients were fitted with a robotic lower leg system, the PowerFoot BiOM, manufactured by iWalk Inc. The PowerFoot uses microprocessors, sensors, a motor, and a carbon-fiber spring to replicate the action of the amputee’s Achilles’ tendon, ankle, and calf muscle. Also programmable with Bluetooth technology, the PowerFoot’s settings can be adjusted by the user via smartphone; like the microprocessor knee, its sensors allow it to adjust to uneven ground and changes in slope or pace.
By the spring of 2012, these innovations – the X2 and X3 microprocessor knees, the Össur Power Knee, and the iWalk PowerFoot BiOM – were being used in combination, not experimentally but as part of the standard of care for service members and veterans. The PowerFoot enables many with an advanced prosthetic knee to walk with an almost natural-looking gait.
In April, when the Walter Reed staff invited several journalists to meet recipients of this prosthetic knee-ankle combination, an elevator got stuck during the visit. The group – doctors, journalists, and two Marine amputees – got out to climb a flight of stairs. The Marines moved only slightly more slowly than everyone else.
Toward a Bionic Limb
Because the overwhelming majority of service-related amputations have involved the lower limb, it shouldn’t be surprising that the recent surge in development has produced prosthetic legs that have turned limpers into sprinters and marathon runners. For several reasons, the functions of the upper extremity are more difficult to replicate: A fully functioning hand, which provides so much of one’s sensory and motor interface with the world, requires the body’s finest degree of motor control, and is articulated on a wrist that rotates 180 degrees. Current prosthetics technology allows upper limb amputees to flex and extend the elbow, open or close a hand, and rotate the wrist – three “degrees of freedom” or independent joint movements. It’s not much movement, and it’s not very fluid.
Air Force Tech Sgt. Joe Deslauriers, who was injured in Helmand province, Afghanistan, on Sept. 23, 2011, learns the intricacies of his new arm at the Walter Reed National Military Medical Center. The DEKA arm has 10 degrees of movement, and features moving fingers, wrist, elbow, and shoulder; all those parts move with electric motors, which are controlled by the user with signals from a foot- and shoulder-based controller. U.S. Army photo by Rob McIlvaine
The Defense Advanced Research Projects Agency (DARPA), to improve the quality of life for upper limb amputees, launched its Revolutionizing Prosthetics program in 2006, with the ambitious goal of creating an upper limb with full motor and sensory abilities that responds to direct neural control – to be moved, in other words, by the wearer’s thoughts. Even today, as the program’s first outcomes are being demonstrated, such an innovation sounds like science fiction. But the first few years have produced astonishing results.
The first of two major projects funded by DARPA was an arm designed by DEKA Research and Development Corporation in New Hampshire. Completed about a year ago, the DEKA arm has undergone about 4,000 hours of tests in which subjects were able, through the use of controls activated by the foot and the shoulder, to exercise about 10 degrees of freedom. DEKA arm users can turn a key, use a power tool, or raise the arm overhead.