WASHINGTON - A bionic prosthetic arm that is controlled by its operator's thoughts and feels like the amputee's lost limb went on display at a major US science conference. 

More than 50 amputees worldwide, many of them military veterans whose limbs were lost in combat, have received such devices since they were first developed by US doctor Todd Kuiken in 2002.

The arm uses technology called Targeted Muscle Reinervation (TMR), which works by rerouting brain signals
from nerves that were severed in the injury to muscles that are working and intact.

"What we do is use the nerves that are still left," Kuiken said on Thursday. "Muscle becomes the biological amplifier."

Glen Lehman, a retired US military sergeant who lost his arm in Iraq, demonstrated the latest technology at the annual conference of the American Association for the Advancement of Science in Washington.

"It feels great, if feels intuitive. It is a lot better than the other prosthetic I have now," said Lehman, whose forearm and elbow were blown off in a Baghdad grenade attack in 2008.
 

After the residual limb heals adequately, the doctor may write a prescription to get a temporary prosthesis. This is the first step in the rehabilitation process.

The process begins with the prosthetist taking a series of measurements of the residual limb. This is done to ensure a comfortable fit of the socket, which will be customized to the residual limb exactly. The socket is the hollow part on the top of the prosthesis into which the residual limb is placed; the socket is the interface between the residual limb and the prosthesis.

The temporary prosthesis is typically not cosmetically finished since adjustments will need to be made as the residual limb continues to decrease in size. Most times different prosthetic components will be used in a temporary prosthesis than will be used in a definitive prosthesis. The temporary will usually be heavier and bulkier than a definitive prosthesis.

Definitive Prosthesis:

Within several months after the residual limb has reached a stable size and shape, you will be evaluated for a definitive (or long-term) prosthesis, which can be more cosmetically finished than the temporary prosthesis. Fabricating and fitting of this prosthesis will require numerous visits and can take a few weeks to complete.

The terms "permanent" or "definitive" prosthesis can be misleading. Unfortunately, no artificial limb is going to last the rest of your life. Depending on daily use and activity level, a prosthesis can last anywhere from two to five years. With children, the time frame is even shorter due to their continuous physical growth. It is important to remember that a prosthesis is a mechanical device and may break down from time to time. It is a sophisticated tool to help restore function that might not otherwise be possible. Major fluctuations in weight or volume can also require adjustments to be made to the socket or other changes may be necessary in other parts of the prosthesis.