Lidoderm patches can be effective for superficial pain syndromes in areas where there is not too much tissue. Sometimes pain is caused by activation of nerve sensors in superficial areas, like wrists, feet, hands, etc. The lidocaine can penetrate to those areas and help with pain. In other areas, the Lidocaine does not reach specific nerves. Placing it on your back will not likely have an effect on your nerve roots,which are much too deep. Usually the drug is absorbed into the bloodstream in those cases and the effect is more a systemic one, similar to an IV Lidocaine infusion.