Evaluation of transcutaneous electrical nerve stimulation parameters for rehabilitation of median and ulnar nerve injury

Abstract: The rehabilitation techniques currently available for patients who suffer from injury to the ulnar or median nerve tends to give suboptimal results. Typically, adults who are operated due to a complete transection of the median or ulnar nerve never regain normal sensibility in the injured hand leading to severe limitations in terms of hand function. One of the biggest challenges in sensory rehabilitation is to keep the nerve cells in the somatosensory cortex active during the process of axon regeneration (phase 1), as the neurons otherwise relocate their resources, which is very hard to reverse. Transcutanous electrical nerve stimulation (TENS) can stimulate the peripheral nerve and thus also stimulate the nerve cells normally receiving sensory information from the hand during phase 1, utilizing what is called referred sensations. This report presents an evaluation of how different input parameters; pre-pulse amplitude, pulse amplitude and frequency, affect the experienced hand sensations created by a TENS device. The study is based on data collected from tests performed on 29 healthy adults, where the perceived sensations were characterized in terms of location, naturalness, intensity and type of sensation using a stimulation pattern randomizing program. In addition, the equipment was tested on three patients who had undergone surgical repair of the median or ulnar nerve. The results show that there is a clear correlation between the input parameters pre-pulse and pulse amplitude and the sensory feedback. The sensation intensity increases with the amplitude, and the opposite relationship was found for experienced naturalness. The patient testing suggested that the technique has potential as a rehabilitation method.