This is a type of nerve block that is performed to determine if there is damage to the sympathetic nerve chain, a network of nerves extending the entire length of the spine. These nerves control some of the involuntary functions of the body, such as opening and narrowing blood vessels.
The sympathetic nerves run on the front surface of the spinal column (not in the spinal canal with the nerves from the central nervous system). The sympathetic nerves are part of the autonomic nervous system which controls basic functions. In other words, the autonomic nervous system is responsible for controlling things people do not have to think about or have direct control concerning their function. However, there is a connection between the central and autonomic nervous systems. Sometimes arm or leg pain is caused by a malfunction of the autonomic system secondary to an injury.
A sympathetic nerve block involves injecting medicine around the sympathetic nerves in a lumbar (back) or cervical (neck) area. By doing this, the system is temporarily blocked in hopes of reducing or eliminating pain. If the initial block is successful, then additional blocks are generally repeated until the pain diminishes.