Quantification of isolated muscle compartment activity in extrinsic finger muscles for potential prosthesis control sites

Prosthetic hands are becoming more advanced and gaining degrees-of-freedom similar to their human counterparts. However, the command interface enabling control of these prostheses needs to be improved for more intuitive functional use. One barrier to using electromyographic (EMG) signals as the command interface is measuring independent muscle control sites in the residual limb. Surface electrodes are commonly used to detect muscle activity in the forearm; however, the measured signals are often comprised of EMG signals from multiple muscles that are close together. This study investigated the suitability of the index and middle finger compartments of the extrinsic muscles as control sites for prostheses using a direct myocontrol interface. Fine-wire intramuscular electrodes were inserted into seven subjects and their ability to achieve isolated activations of each compartment was tested. The results showed five of the six compartments yield signals suitable for independent volitional control. The middle finger compartment of extensor digitorum communis was found to be incapable of isolated contractions and is therefore not recommended as a control site for direct myocontrol prostheses. A cross-correlation threshold was used to verify that simultaneously measured EMG signals were free from crosstalk and were therefore attributed to muscle co-activations.