In the Headlines | Amputation: decode the movements of the ghost member

Most amputees perceive sensations in their missing limbs, hence the name "ghost member". In a previous study, researchers at Aix-Marseille University and Sorbonne University had shown that more than 75% of amputees are able to perform voluntary movements with their ghost members. However, the execution of these "ghost" movements, such as the closure of the fingers or the hand, the rotation or flexion of the wrist, are always badociated with specific muscle contractions at the stump. In arm amputees above the elbow, these contractions involve muscle groups that are unrelated to the mobilized joints prior to amputation, as if muscle reinnervation had occurred spontaneously without surgery.

The team of researchers with doctors (Institute of Intelligent Systems and Robotics CNRS / Sorbonne University, Institute of Movement Sciences – Etienne-Jules Marey CNRS / Aix-Marseille University and Regional Institute of Physical Medicine and Rehabilitation of the UGECAM Nord-Est) has developed algorithms capable of recognizing the muscular activities generated by the mobilization of the phantom limb and to reproduce the motion detected with the prosthesis: an intuitive control, without learning or surgery.

Two arm amputees used this type of control to operate an unworn prosthesis but placed close to their arm stump. The very encouraging results show that the participants were able to master the prosthesis and carry out the exercise after only a few minutes of familiarization with the system, despite longer periods of action. This research is very promising, as arm amputees often have great difficulty controlling their prosthesis effectively, to the point that many of them eventually give up.

The video of a participant in the study

The researchers continue their work by considering moving to prosthesis tests, while also helping to increase knowledge about the phenomenon of the ghost member whose mechanisms are not yet fully understood. Through this study, scientists also show the need to reconsider the phenomenon of the ghost member, usually taboo, often attributed to the mourning of the lost limb and mostly considered from the angle of pain.

The results of this work were published on November 29, 2018 in Frontiers in Bioengineering and Biotechnology.