Engineering news
For people missing a hand, one of the biggest challenges to regaining functionality when using a prosthetic hand is an inability to rotate the wrist. This is an essential movement for many tasks, including using door handles or turning over pieces of paper. Placing a hand face up or down is also difficult.
To tackle the issue, a team of researchers led by Max Ortiz Catalan at Chalmers University of Technology in Sweden set out to provide an alternative to conventional socket prostheses or “cumbersome” wrist rotators.
"A person with forearm amputation can use a motorised wrist rotator controlled by electric signals from the remaining muscles. However, those same signals are also used to control the prosthetic hand," said electrical engineer Catalan.
"This results in a very cumbersome and unnatural control scheme, in which patients can only activate either the prosthetic wrist or the hand at one time and have to switch back and forth. Furthermore, patients get no sensory feedback, so they have no sensation of the hand's position or movement."
Instead, the team’s new approach places implants from Swedish company Integrum into the two forearm bones, the ulna and radius. A wrist-like artificial joint then acts as an interface between the implants and a prosthetic hand, allowing for more natural movements with intuitive controls and sensory feedback.
Conventional socket prostheses prevent wrist rotation, said Catalan.
"Depending on the level of amputation, you could still have most of the biological actuators and sensors left for wrist rotation. These allow you to feel, for example, when you are turning a key to start a car. You don't look behind the wheel to see how far to turn – you just feel it. Our innovation means you don't have to sacrifice this useful movement because of a poor technological solution, such as a socket prosthesis. You can continue to do it in a natural way," he said.
In tests to measure manual dexterity, patients with the artificial joint scored “far higher” than those using conventional socket technology, said contributing biomedical engineer Jason Millenaar.
"Our new device offers a much more natural range of movement, minimising the need for compensatory movements of the shoulder or torso, which could dramatically improve the day-to-day lives of many forearm amputees," said Millenaar's colleague and fellow visiting international student Irene Boni.
The work was published in IEEE Transactions on Neural Systems and Rehabilitation Engineering.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.