A collection of images showing the new technology.
Photograph courtesy of the Biomechatronics and Neurorehabilitation Laboratory/Chalmers University of Technology.
One of the biggest challenges to regaining a high level of function after a transradial amputation is the inability to rotate one’s wrist. A new artificial joint restores wrist-like movements, which could improve the quality of life for people with such an amputation. A group of researchers led by Max Ortiz Catalan, PhD, an associate professor at Chalmers University of Technology, Sweden, have published their research about the development of the joint in the December issue of the journal IEEE Transactions on Neural Systems & Rehabilitation Engineering.
The new joint works with an osseointegrated implant system developed by the Sweden-based company, Integrum AB, a partner in the project. Implants are placed into the ulna and radius and a wrist-like artificial joint acts as an interface between the two implants and the prosthetic hand, which allows for more naturalistic movements, with intuitive natural control and sensory feedback.
People who have lost their hand and wrist often still preserve enough musculature to allow them to rotate the radius over the ulna—the crucial movement in wrist rotation, according to the researchers. A conventional socket prosthesis locks the bones in place, preventing any potential wrist rotation.
“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,” said Ortiz Catalan, who leads the Biomechatronics and Neurorehabilitation Laboratory at Chalmers.
“In tests designed to measure manual dexterity, we have shown that a patient fitted with our artificial joint scored far higher compared to when using conventional socket technology,” said Jason Millenaar, MS, a biomedical engineer who worked on the project.
The researchers found that restoring the full range of movement to all degrees of freedom in which the forearm bones can move was not necessary; the key parameter for returning a naturalistic wrist motion is the axial, or circular, motion of the ulna and radius bones.
“The wrist is a rather complicated joint. Although it is possible to restore full freedom of movement in the ulnar and radial bones, this could result in discomfort for the patient at times. We found that axial rotation is the most important factor to allow for naturalistic wrist movement without this uncomfortable feeling,” Ortiz Catalan said.
To see a video of the device in practice, visit https://youtu.be/yV7vgIpQXLo.
Editor’s note: This story was adapted from materials provided by Chalmers University of Technology.
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