Lumbar Facet In A nerve block is a useful diagnostic tool when it comes to back pain. Your spine specialist may use a nerve block to pinpoint the source of the pain in your back, especially if he or she sees something abnormal on an x-ray or MRI. The procedure for a nerve block starts with a topical anesthetic, and then while you are under conscious sedation, the specialist will guide a needle into the suspected problem area with the help of an x-ray. The doctor will then administer the nerve block. The entire procedure only takes about five minutes, and most of our patients are ready to go home just an hour later. You’ll experience pain relief, but the nerve blocking medication will wear off in a few hours.