TENS (Transcutaneous Electrical Nerve Stimulators) pass an electrical current through the skin over painful areas or over nerves that supply painful areas. They consist of a small control box with leads to gel pads that are placed on the skin. TENS can be helpful for a variety of different pains. There is no way to predict exactly who will find TENS particularly helpful. A trial of TENS is the best way to find this out.
These are devices that are implanted into the body. An electrode sits within the spinal canal and is connected to a control box that sits below the skin. These have a role for some, but usually are considered when many other treatments have been tried.
These require very comprehensive logistical back up and are best inserted and looked after by experienced centres with many practitioners (both medical and nursing) and access to neurosurgical care if required.