TENS pain relief. Patient operating a transcutaneous electrical nerve stimulation (TENS) unit to relieve pain in their knee. The main TENS unit produces minute electrical impulses which are passed into the skin by the two electrode pads. The pulses are supposed to block the nerve signalling pathway, thus preventing pain signals reaching the brain and being felt. Although TENS offers pain relief, it is not a curative therapy. These pads are positioned to relieve pain in the knee joint.