An Irish neural engineer has played a key role in the development of the latest type of artificial arm, writes David Labanyi
Four years ago electrician Jessie Sullivan from Tennessee in the US had his arms amputated at the shoulder after getting a shock while working on power cables.
Months after the amputation, he went to the Rehabilitation Institute of Chicago (RIC) to be fitted for a prosthesis, despairing that he would never live independently.
At the RIC Sullivan met Dr Todd Kuiken, director of the neural engineering centre for artificial limbs, where they discussed new research that was taking place.
This led to Sullivan being fitted with a myoelectric arm controlled by nerve signals from the brain. He can now cut hedges, sweep the floor and feed himself.
Behind the new technology is a team of researchers, including Dr Madeline Lowery, a lecturer in the School of Electrical, Electronic and Mechanical Engineering at UCD. She worked at RIC for five years.
"When I joined RIC the project with Jessie Sullivan was just beginning. One of the first questions that we looked at was modelling the EMG signals from the nerve-muscle grafts to test the feasibility of this new approach."
Her role was to develop computer models of the electrical signals from the nerve-muscle grafts and to look at different ways of analysing these signals.
The basis of the new technology are the nerves which used to run to the arm, which even after a limb is amputated, still carry information.
Many artificial limbs are controlled using myoelectric signals from just a pair of muscles in the damaged arm. While effective, this technology only allows one motion at a time, whereas normal human arm function involves co-ordinated, simultaneous movements.
What researchers at RIC wanted to do was harness the extra information available in the nerves and use it to allow the person operating the artificial limb more precise control.
"The solution for Jessie was to connect these nerves into muscle that is redundant in an amputee patient. So, in the case of Jessie, where he has an amputation at shoulder level, the pectoral muscle doesn't really perform any function," says Lowery.
Surgeons dissected the four major nerves that used to run down Sullivan's arms and transferred them to different parts of his chest muscles. After about six months these nerves grew into the muscles.
Now, using these muscles, Sullivan can operate the artificial arm by thinking of the movement he wishes to make. These thoughts cause different parts of his chest muscles to contract and electrodes read these movements and relay the instruction to the arm.
"When he thinks 'extend the elbow', a signal will travel down along the nerve that used to go to the arm muscles that would do that but it now causes a small region of his pectoral muscle to contract," she says.
The arm works on proportional control so the bigger the electrical signal the muscle generates, the harder it contracts. This allows Sullivan to pick up and hold a can without crushing it.
It also allows simultaneous movements of the hand, wrist and elbow, something that was beyond previous prosthetic limbs.
Sullivan's was the first nerve-muscle graft used to control an artificial limb. Since then, there have been three more and the US army, in particular, is interested in the research.
It recently allocated a significant, undisclosed amount of funding to the research.
This is because injured soldiers, like car crash victims and workplace accident victims, are the most likely beneficiaries of the research.
The Defense Advanced Research Projects Agency has recently injected a large amount of money into upper limb prosthesis research. Soldiers returning from Iraq are now more likely to survive attacks, but because of the way the body armour is designed, they suffer a high incidence of amputations.
Lowery's role was to build computer models of the arm and how it would work before it was fitted.
"Before we went into humans we built computer models to try to simulate the signals to see if you could record multiple signals from the different nerve grafts. We also had to examine the effect of muscle, fat and bone in the transmission of electrical signals from the nerves."
According to Kuiken, the models developed by Lowery are among the most sophisticated ever made.
"These allowed us to study how electric signals generated by muscle [ EMG signals] move through the body. This is important to our research because we use these little electrical signals to control the artificial arm," he says.
"Dr Lowery developed models that helped us to determine how big a signal would be coming from what muscle. We also used this data to decide about how big a piece of muscle we needed in our nerve transfer surgeries."
The result of the research is that Sullivan can make 28 different movements.
The next stage of this research is safety. As the movements possible by an artificial limb become more detailed and swifter, researchers have to ensure the design will never injure the amputee.
"If someone is bringing a fork close to their face we can use a sensor to recognise if it is too close to the wrong area of the face," says Lowery.
"This can be done by motion sensors, with safety switches, or thresholds on the range of motion of device."
While the number of people affected by upper arm amputations is relatively small, the level of disability is huge. In the US 166,464 people lost at least a part of an upper limb during the period from 1988 to 1996, mostly due to road and work accidents and violence, including combat injuries.