They were designed to create electrical impulses in damaged tissue, or route weak nervous signals around nonfunctional tissue. Although they were very sophisticated devices, it could take several days and even weeks to master their use and even then, patients rarely recovered one hundred percent of their mobility.
Lieutenant Worf also used the bands following his spinal injury in 2368, but he had little patience for learning how to use them. He contemplated ritual suicide before turning to the risky genetronic replicator as treatment. (TNG: "Ethics")