Facet joint injections and medial branch nerve blocks aim to diagnose and/or treat pain arising from facet joints in the spine. While facet joint injections are given directly into the facet joint, medial branch blocks target the medial branch nerves that carry pain signals from the facet joints to the brain.

Facet joints are surrounded by a joint capsule made up of synovial membrane tissue.

This joint capsule contains a rich innervation of nerves and its upper pad is typically fused with the fatty sheath of the spinal nerve.

When the synovial membrane tissue of the joint capsule is inflamed, facet joint injections may inhibit the production of inflammatory chemicals, reducing pain, while also making pain receptors less sensitive, in turn sending fewer pain signals through the nerves

More than one injection may be given to treat pain stemming from several facet joints.

Medial branch nerves feed out of the spinal nerves’ dorsal rami and typically possess only sensory properties (except for some small branches in the neck that control small muscles). Medial branch nerves innervate the facet joints. All joint segments below C2-C3 receive medial branch innervation from two levels—the same level as the joint and from a level above the joint.

Injecting steroids near the medial branch nerves may:

• Inhibit the nerve from sending pain signals to the brain
• Block specific fibers (C fibers) within the nerve that results in a decrease in pain transmitted to the brain
• Decreases the permeability of nerve fibers to receive blood, decreasing pain transmission

All the medial branch nerves innervating a joint are treated at the same time. For both types of injection treatments, diagnostic injections include the injection of an anesthetic medication in order to accurately locate the painful facet joint or the corresponding medial branch nerve(s).

Fluoroscopy or ultrasound guidance is done to guide the needle to the accurate treatment region. A contrast dye may be used to enhance the visualization of the joint and/or nerves.