A nerve block normally consists of two medications, a numbing agent like novocaine and a corticosteroid like celestone. It can be placed through the lamina of the vertebra above the dural membrane (an epidural steriod injection or ESI) or through the foramen (a selective nerve root block or SNRB). The injection normally serves two purposes, diagnosis and treatment.
The diagnostic portion of the block is the numbing portion. When you go to the dentist and have an injection in your jaw, he or she is blocking the sensory nerve to the jaw. The numbness lasts approximately three hours. The same principle occurs in your back or neck. If one particular nerve or area is suspected of causing pain, this block will temporarily numb the painful nerve or area. If there is relief noted in the first three hours, this block has successfully diagnosed the problem.
The steroid is the second medication in the injection. This medication can take up to three days to work. It does so by reducing inflammation to the nerve. Relief can last up to six months but in some individuals, relief may not occur. It is unfortunately unpredictable.