A lumbar sympathetic block is an injection of a local anesthetic around a set of particular nerves in the lower back. It is typically used for pain in the leg(s) and/or hip(s).

Lumbar sympathetic blocks are used to treat pain caused by overactive nerves called sympathetic nerves. These nerves can become hyperactive for a number of reasons. Sometimes, hyperactivity of these nerves is a normal and healthy response of the body to help itself heal from injury. At times, however, these nerves remain hyperactive longer than they should, and this can lead to a chronic pain syndrome. One example of such a pain syndrome is RSD. Lumbar sympathetic blocks are used in these conditions to decrease the hyperactivity of these nerves which can then lead to a substantial reduction in pain. This injection often needs to be performed in a series (typically once weekly for an average of 6 weeks), in order to “retrain” those nerves to fire normally. This retraining process is called neuromodulation.