A medial branch block is an injection of a strong local anesthetic on the medial branch nerves that supply the facet joints. The facet joints, also known as the zygapophysial joints, are part of the bony framework of the spine. They are small bony projections from one vertebra meeting with similar bony projections from the vertebra above or below. Sometimes, due to a variety of acute and chronic conditions, the facet joints can become inflamed. For lower back (lumbar) facet joints, the pattern of pain is usually an achiness in the low back, radiating across the lower back and slightly down the back of the buttocks and upper thighs. Usually, standing or bending backward worsens the pain. For neck (cervical) facet joints, the pattern of pain is an achiness in the neck, slight radiation across the neck and shoulders, and worsening symptoms with turning the head from side to side or looking up.