A team of bioengineers have developed a prosthetic arm that is able to detect nerve signals in the spinal cord. By imagining they are controlling a phantom arm, patients create electrical signals in the spinal motor neurons that can be detected by the arm’s sensor technology and used as commands.

The robotic arm prosthetics currently available are controlled by the patient twitching the remnant muscles in their shoulder or arm. The technology in said arms is fairly basic and able to perform only or two grasping commands. Said limitations have led to a global 40-50% discard rate for such prosthetics.

The new prosthetic is potentially capable of far more commands due to its use of sensor technology. The research suggests that the signals sent by spinal motor neurons can be detected in much greater amounts than with remnant muscle fibre, meaning that the arm can ultimately be programmed with more commands to increase the functionality.

“When an arm is amputated the nerve fibres and muscles are also severed, which means that it is very difficult to get meaningful signals from them to operate a prosthetic,” said lead author Dr Farina, from the Department of Bioengineering at Imperial College London.

“We’ve tried a new approach, moving the focus from muscles to the nervous system. This means that our technology can detect and decode signals more clearly, opening up the possibility of robotic prosthetics that could be far more intuitive and useful for patients. It is a very exciting time to be in this field of research.”

The researchers experimented in the lab with six volunteers who were either amputees from the shoulder down or just above the elbow. Following physiotherapy training, all six were able to make a more extensive range of movements than would be possible using a classic muscle-controlled robotic prosthetic.

The volunteers underwent a surgical procedure at the Medical University of Vienna that involved re-routing parts of their Peripheral Nervous System (PNS), connected with hand and arm movements, to healthy muscles in their body. Depending on the type of amputation, this re-routing was either directed to the pectoral muscle in the chest or the bicep in the arm.

Researchers suggested that the current model is still subject to refinement, but could be on the market in the next three years.

The laboratory tests have taken them to the end of the proof of concept stage and they will now begin involve extensive clinical trials with a much wider cross section of volunteers in order to make the technology more robust.

Much of Dr Farina’s research was carried out while at the University Medical Centre Gottingen and research was conducted in conjunction with Dr Farina’s co-authors in Europe, Canada and the USA. The work was supported by the European Research Council, the Christian Doppler Research Foundation of the Austrian Federal Ministry of Science, Research and Economy and the European Union’s Horizon 2020 research and innovation programme.