The wars in Southwest Asia, where blast-related amputations reached a new high as a percentage of combat injuries, pushed prosthetics R&D and implementation to previously unimagined levels. Now military, Department of Veterans Affairs (VA), industry and academic researchers are close to bringing to practical application technologies previously seen only in science fiction.
“All of the advances we’ve had since 9/11 were motivated by injuries from that war. Most prosthetic development in the past has been the result of war, starting with lower extremities during and after World War II,” according to Dustin J. Tyler, Ph.D, associate professor of biomedical engineering at Case Western University and a biomedical engineer at the Cleveland VA Medical Center.
“With all the improved body armor in this conflict, people survived blasts that would have killed them in the past, but experienced greater loss of limbs. That motivated most commercial companies to work on more articulated hands.”
Those efforts include so-called “mind control” techniques, in which brain activity and messages to the nerves controlling a limb are mapped, translated into computer code, and fed into a robotic prosthetic, which then mimics the movements the lost limb would have performed. Successful or promising tests of this technology began on lab monkeys but soon moved to humans with amputations or spinal dysfunctions, whether caused by injury or disease.
Other cutting-edge approaches to help overcome limb dysfunction include:
- Direct interface to the nervous system – enabling not only controlled movement of a robotic hand, but also returning the patient’s sense of touch
- Pattern recognition – using “muscle memory” to help prosthetic movement
- Muscle reinnervation – the higher the amputation, the more of the muscles and nerves are missing, but they can reconnect to muscles that no longer have a use, such as biceps if the forearm is missing
- Permanent implants – linking prosthetics to the patient’s nerves, muscles, and bones
- Better power systems – greater energy densities and management, in a small, lightweight form factor
- Self-repairing materials – improving prosthetic durability while reducing maintenance needs
- Non-slip materials – giving a prosthetic hand the ability to not only grip an object, but hold onto it without slipping
- Sensor skin – artificial skin with built-in nanosensors that can mimic human skin’s ability to sense – and usually identify – anything it touches
- 3-D printing – using additive manufacturing to create components or complete prosthetics
- Exoskeletons – developed to help warfighters lift and carry heavy items or travel long distances without tiring or straining human muscles, but with obvious potential applications to paraplegics, quadriplegics, and amputees
- Direct skeletal prosthesis (osseointegration) – a direct structural and functional connection between ordered, living bone and the surface of a load-carrying implant
- Intelligent powered robotic limbs – next-gen powered limbs with the ability to stably respond to disturbances or changing terrain
“The new generation [in the United States] is much more of a savvy, tech-integrating society. But there is still a huge stigma to robotics elsewhere in the world. I think we have to be careful, even in the U.S., about people accepting these new technologies in the long run, when it comes down to ease of use,” Tyler said. “The fundamental challenge for future generations is we are still way behind the information content available within the normal human neuromuscular system.
One surgeon said a young soldier who could expect his injured leg to have about 85 percent of its former capability demanded it be amputated and replaced with a cutting-edge prosthetic some have rated at 120 percent of normal human ability.
“The challenge is to develop technology that can interact at the same level of fidelity, in either stimulating or recording. We don’t have a technology that can connect living nerves across a break. The body also tries to destroy or wall off foreign elements we try to implant. Conceptually, jumping the gap is a good idea, but there is a lot of work yet to be done to make it work properly. And spinal cord injury or any disease that interferes with neural transmission has the most to gain from that.”
According to Frederick Downs Jr., a prosthetics consultant for the Paralyzed Veterans of America and former national director of the VA’s artificial limb program for 30 years, advances in lower limb prosthetics have always come first, largely due to economics, but also to the greater difficulties in artificially replicating the complex movements and capabilities of the human hand.
“Last year we bought about 12,000 lower limb prosthetics and only 150 upper limbs. When I took over the VA program, lower limbs came from World War II and there weren’t many upper extremities because the blast that would cause that damage also killed the warfighter,” he explained. “Today, body armor has improved significantly, as has the quality of medical care far forward. And the survival rate for both lower and upper extremities has improved dramatically in the past 10 or 15 years.