Artificial joint restores wrist movements of forearm amputees

A new artificial joint restores significant wrist movements of forearm amputees, which could significantly improve their quality of life. A group of researchers led by Max Ortiz Catalan, associate professor at the University of Technology Chalmers, Sweden, published his research in the journal IEEE Transactions on Neural Systems and Rehabilitation Engineering.

For patients who miss a hand, one of the biggest challenges in regaining a high functional level is the inability to rotate one's wrist or "pronate" and "supinat". When you lay your hand flat on a table, palm down, it is fully pronounced. Turn your wrist 180 degrees, so that the hand is palm up and that it is totally supine.

Most of us probably take it for granted, but it's an essential movement that we use every day. Remember to use a doorknob, a screwdriver, a knob on a stove or simply turning over a piece of paper. For those who have lost the hand, these are much more delicate and uncomfortable tasks, and current prosthetic technologies provide only limited relief to this problem.

"A forearm amputee can use a motorized wrist rotator controlled by electrical signals from the remaining muscles, but these same signals are also used to control the prosthetic hand," says Max Ortiz Catalan, professor Associated with Chalmers Electrical Engineering Department.

"The result is a very cumbersome and unnatural control scheme, in which patients can only activate the prosthetic wrist or the hand at the same time and only have to tilt one after the other. patients do not receive any sensory feedback, so they have no feeling of position or movement of the hand ".

The new artificial joint works instead with an osseointegrated implant system developed by the Swedish company Integrum AB – one of the partners of this project. An implant is placed in each of the two bones of the forearm – the ulna and the radius – and then an artificial wrist-shaped joint acts as an interface between these two implants and the prosthetic hand . Together, this allows for much more naturalistic movements, with intuitive natural control and sensory feedback.

See a video of the joint in action here.

Patients who have lost their hand and wrist often still retain enough musculature to be able to rotate the radius on the ulna – the crucial movement of wrist rotation. A conventional prosthesis, attached to the body by the compression of the stump, blocks the bones in place, thus preventing any potential wrist rotation and thus spoiling this useful movement.

"Depending on the level of amputation, it is possible that most actuators and biological sensors are left for wrist rotation, allowing you to feel, for example, when you turn a key to start a car. You do not look back at the wheel to see where to turn – you feel it.Our new innovation means that you do not have to sacrifice that useful motion because of a mediocre technological solution, such as that. an interlocking prosthesis You can continue to do this in a natural way, "says Max Ortiz Catalan.

Biomedical engineers Irene Boni and Jason Millenaar were in Chalmers as visiting foreign students. They worked with Dr. Ortiz Catalan in his biomechanics and neurorehabilitation laboratory in Chalmers, and with Integrum AB on this project.

"In tests designed to measure manual dexterity, we showed that a patient equipped with our artificial joint achieved results far superior to those of a conventional plug-in technology," says Jason Millenaar.

"Our new device provides a much more natural range of motion, minimizing the need for compensatory movements of the shoulder or torso, which could dramatically improve the daily lives of many forearm amputees," explains Irene Boni.

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Dr. Marco Controzzi from the Biorobotics Institute of the School of Sant 'Anna (Italy) Graduate School also participated in the research.

Read the document "Restoring the natural rotation of the forearm in osteo-integrated transradial amputees". published in the newspaper IEEE Transactions on Neural Systems and Rehabilitation Engineering.

More about research

Dr. Max Ortiz Catalan is Associate Professor at the Chalmers University of Technology, Sweden, and Head of the Laboratory of Biomechatronics and Neurorehabilitation (@ChalmersBNL)

Irene Boni was a visiting student from the School of Advanced Studies Sant? Anna in Italy and Jason Millenaar from the University of Technology Delft in the Netherlands.

The researchers found that it was not necessary to restore all the movements at all degrees of freedom in which the forearm bones could move – the key parameter for to obtain a naturalistic movement of the wrist is the "axial" or circular movement of the ulna and the radius. bones.

"The wrist is a rather complicated joint, and although it is possible to regain complete freedom of movement in the ulnar and radial bones, this could cause discomfort for the patient." We found that axial rotation was the most important factor. the most important allowing naturalistic movement of the wrist without this uncomfortable feeling, "says Max Ortiz Catalan.

The development was finalized as part of the Horizon 2020 framework program for research and innovation under the DeTOP project.

For more information, contact:

Max Ortiz Catalan, Department of Electrical Engineering, Chalmers University of Technology, Sweden, +46 70 846 10 65, [email protected]