One of the causes of pain that passes into the extremities is irritation of one or more nerve roots. The purpose of a Selective Nerve Root Block (SNRB) is to specifically block one or more spinal nerves to decrease pain. This is done by injecting an anesthetic and anti-inflammatory steroids into the space around the nerve for the nerve block.
A Selective Nerve Root Block is similar to an epidural steroid injection, but is more specific. This will help determine which particular nerve is related to your symptoms.