What Is a Medial Branch Block?

A medial branch block is a medical procedure where an anesthesiologist numbs the medial branch nerves emerging from the spinal cord to determine if they are a source of chronic pain. These nerves emerge from the facet joints between the vertebrae and can be a significant source of pain. The procedure will temporarily reduce pain if the facet joints are the problem, indicating that a procedure to sever or ablate the nerves could be beneficial for long term pain management. Medial branch blocks are not therapeutic or curative, serving a primarily diagnostic effect.

Before the test, the doctor will interview the patient to check for allergies and other contraindications. For the procedure, the patient lies on a table and receives intravenous sedation for comfort. Once the sedatives take effect, the doctor can clean an area of interest along the spine and insert a needle, using fluoroscopy for guidance to make sure the needle goes to the right place. The doctor can inject a tracer dye to confirm the placement. Next, she adds an anesthetic to temporarily block the nerve.

The doctor asks the patient to wait 20 to 30 minutes for the anesthetic to take effect, and then has the patient engage in an activity that is usually painful, such as bending or stretching. If the problem is with the facet joints, the medial branch block will limit pain signals, allowing the patient to complete the task without pain, or with minimal pain. This pain-free state will last until the anesthetic wears off and the nerves are able to function again.

When the medial branch block works, the doctor knows that treating the nerves around the facet joints should help with the patient's chronic pain. Doctors can use lasers and other tools to burn the nerves and carefully cut off their signals in a neurotomy procedure. The patient should experience dramatically reduced pain levels after surgery and may be more able to engage in physical activities.

In cases where the medial branch block has no or little effect, the problem lies somewhere else in the patient's body, and more diagnostic testing is necessary to find out what is happening. Failure of a medial branch block indicates that severing the nerves would not provide any benefits to the patient. The doctor may repeat the test at another time to see if anything changes, depending on the situation and how well the patient responds to other treatments.