Click-on prosthetic limb

Surgeons attach click-on, mind-controlled prosthetic arm

Image credit: Radboud University

Clinicians based at Radboud University in the Netherlands have successfully attached a click-on robotic arm which uses Bluetooth to allow patients to control it with their thoughts.

In 2010, truck driver John Baggerman was involved in a serious road accident, and had his arm amputated. Now he has become the first person in the Netherlands – and among the first in the world – to use a new type of robotic arm.

Normally, prosthetic limbs are attached using a prosthetic socket. These are often uncomfortable, can cause skin problems, are difficult to put on and take off, and can let the prosthesis slip off.

This new prosthetic limb, however, is clipped directly onto the bone. A similar technique has been used for prosthetic legs, having been introduced to the Netherlands in 2009. However, good prosthetic arms and hands require more precise movements, and have presented a greater challenge.

The prosthetic requires three surgeries and long periods of rehabilitation to become fully functional. The first surgery inserts a metal rod into the bone, and the second screws in a connecting rod. The surface of the metal rod is textured, allowing it to be accepted by the existing bone.

For robotic prostheses to function, they must be able to detect signals from the patient’s nerves or muscles and relay these signals to the prosthetic.

The final, most complex surgical stage – attaches nerves that controlled muscles in the hand to the stump of the upper arm. This is called Targeted Muscle Reinnervation surgery. Connecting nerve to muscle allows the muscles to act much like an amplifier for nerve signals.

After these surgeries, the patient must spend a period of time perfecting their movement-through-thought. Imagining opening and closing the hand makes the muscles in the upper arm contract.

Muscular activity in the upper arm is measured by electrodes wrapped around the upper arm like a bracelet. Once the nerves have grown enough into the muscle, the muscle signal will become strong enough to be detected by the sensor in the electrodes.

The robotic arm, which is controlled via Bluetooth, can therefore be induced to move using thoughts alone.

“All movements can be made with the shoulder,” says rehabilitation Henk van de Meent, one of the clinicians who first introduced this type of prosthesis to the Netherlands. “This gives the patient a larger range of motion. Another advantage is that the click-on prosthesis is attached easily and quickly.”

This prosthesis is not yet widely available, and eligibility will be determined on a patient to patient basis.

While various robotic, mind-controlled prosthetic arms have been developed previously, such as the Boston Digital Arm, and John Hopkins University’s Proto 1 and Proto 2, which allow for fine movements, this prosthetic arm stands out for clipping directly into the bone. This is still uncommon for prosthetic limbs.

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