Transradial Implant Provides Dexterity, Touch to Prosthesis

A patient with a transradial amputation has become the first recipient of an osseoneuromuscular implant to control a dexterous hand prosthesis. In a pioneering surgery, titanium implants were placed in the radius and ulnar bones of the woman’s arm, from which electrodes to nerves and muscle were extended to extract signals to control a robotic hand and to provide tactile sensations. This makes it the first clinically viable, dexterous and sentient prosthetic hand usable in real life, according to the members of the European Commission project called Dexterous Transradial Osseointegrated Prosthesis with neural control and sensory feedback (DeTOP).

The new implant technology was developed by a team led by Max Ortiz Catalan, PhD, at Integrum AB, a Swedish medical device company, and Chalmers University of Technology, Gothenburg, Sweden. This first-of-its-kind surgery, led by Rickard Brånemark, MD, PhD, and Paolo Sassu, MD, PhD, took place at Sahlgrenska University Hospital in Gothenburg.

Conventional prosthetic hands rely on electrodes placed over the skin to extract control signals from the underlying muscles of the residual limb. These superficial electrodes deliver limited and unreliable signals that only allow control of gross movements such as opening and closing the hand. Richer and more reliable information can be obtained by implanting electrodes in all remaining muscle within the residual limb instead, according to the researchers. Sixteen electrodes were implanted in this first patient to achieve more dexterous control of a novel prosthetic hand developed in Italy by the Scuola Superiore Sant’Anna and Prensilia.

By implanting electrodes in the nerves that used to be connected to the lost biological sensors of the hand, researchers can electrically stimulate these nerves in a similar manner as information conveyed by the biological hand. This results in the patient perceiving sensations originating in the new prosthetic hand, as it is equipped with sensors that drive the stimulation of the nerve to deliver such sensations.

One of the most important aspects of this work, according to the researchers, is that this is the first technology usable in daily life rather than limited to a research laboratory. Integrum AB and Chalmers University of Technology have previously demonstrated that control of a sentient prosthesis in daily life was possible in people with transhumeral amputations using similar technology. This had not been possible in people with transradial amputations where there are two smaller bones rather than a single larger one as in the upper arm. This posed several challenges to the development of the implant system; however, it presented an opportunity to achieve more control of an prosthesis as there are more muscles are available to extract neural commands.

Because the bones in the patient’s arm had weakened from disuse, she is following a rehabilitation program to regain the strength before fully loading the prosthetic hand. In parallel, she is also relearning to control her missing hand using virtual reality, and will begin using a prosthetic hand with increasing function and sensations in her daily life in few weeks. Two patients in Italy and Sweden will also receive the implant surgery in the upcoming months.

“Several advanced prosthetic technologies have been reported in the last decade, but unfortunately they have remained as research concepts used only for short periods of time in controlled environments,” said Ortiz Catalan, an associate professor at Chalmers University of Technology and head of the Biomechatronics and Neurorehabilitation Lab, who has led this development for ten years. “The breakthrough of our technology consists of enabling patients to use implanted neuromuscular interfaces to control their prosthesis while perceiving sensations where it matters for them, in their daily life.”

Editor’s note: This story was adapted from materials provided by Chalmers University of Technology.