Prosthetic implant provides realistic wrist movement to amputees

Users of prosthetic hands often find one common movement particularly difficult or even impossible: pronation and supination. These are the movements enabled through rotation of the wrist, such as turning the hand from palm down to palm up on a flat surface. For able-bodied people, such movements are extremely common, useful tasks such as turning a door handle or using tools.

But such movements are very difficult to replicate using conventional prosthetics. Those which attach to the remaining stump using a socket tend to lock the forearm bones – the radius and ulna – in one position, rendering rotation impossible. Even motorised prosthetics have problems.

"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 Max Ortiz Catalan of the Department for Electrical Engineering at Chalmers University of Technology in Sweden. "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."