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Currently available prosthetic hands are capable of actuating anywhere from five to 30 degrees of freedom (DOF). However, grasp control of these devices remains unintuitive and cumbersome. To address this issue, we propose directly extracting finger commands from the neuromuscular system. Two persons with transradial amputations had bipolar electrodes implanted into regenerative peripheral nerve interfaces (RPNIs) and residual innervated muscles. The implanted electrodes recorded local electromyography with large signal amplitudes. In a series of single-day experiments, participants used a high speed movement classifier to control a virtual prosthetic hand in real-time. Both participants transitioned between 10 pseudo-randomly cued individual finger and wrist postures with an average success rate of 94.7% and trial latency of 255 ms. When the set was reduced to five grasp postures, metrics improved to 100% success and 135 ms trial latency. Performance remained stable across untrained static arm positions while supporting the weight of the prosthesis. Participants also used the high speed classifier to switch between robotic prosthetic grips and complete a functional performance assessment. These results demonstrate that pattern recognition systems can use intramuscular electrodes and RPNIs for fast and accurate prosthetic grasp control.

Current prosthetic limbs offer little to no sensory feedback. Developments in peripheral nerve interfaces provide opportunities to restore some level of tactile feedback that is referred to the prosthetic limb. One such method is a Regenerative Peripheral Nerve Interface (RPNI), composed of a muscle graft wrapped around a free nerve ending. Here, we characterize perception and discomfort thresholds, as well as sensitivity to stimulation through two-alternative forced choice discrimination tasks. One person with transradial amputation who had one RPNI constructed from the median nerve and two constructed from the ulnar nerve participated. Average perception thresholds across all RPNIs were between 950 and 1120 nC with variance of less than 350 nC over a 36-month period. Discomfort thresholds were from 3880 nC to 9770 nC across all RPNIs. The just noticeable difference for the Median RPNI was 520 nC, larger than either the Ulnar-1 or Ulnar-2 RPNIs (210 nC, 470 nC, respectively). We also calculated Weber fractions to compare sensitivity between different RPNIs and relate our results to previous studies. Weber fractions for each of the Median, Ulnar-1, and Ulnar-2 RPNIs were 0.134, 0.088, 0.087, respectively. This work is the first to quantify the functional stimulation range and sensitivity of RPNIs in a human participant. Future work will focus on characterizing RPNI sensation in additional individuals to determine if these findings are generalizable to the amputee population.