The z-joints, also called the facet joints, are located in the back of the spine and prevent excessive twisting of the spine in the low back, and excessive extension in the neck. Damage to the joints can occur due to trauma (automobile accidents, falls), arthritis, infection, reduced disc height, or in the low back: repetitive lifting of heavy objects for many years. Usually the facet joints in the low back carry about 15% of the weight on the spine, but in cases where the disc is very narrow, the weight load may increase to 65%. The facets can have damage to the cartilage lining, overgrowth of bone (bone spurs), fractures through the joint, tears in the thick fibrous capsule over the joints, or can have bruising or bleeding into the joints. Pain from the facets cannot be diagnosed by x-ray, CT scan, MRI, or Bone scan. The diagnosis is made by precision injection of a local anesthetic or other substance onto the medial branch nerve (nerve to the facet joints). If your pain is relieved 80% or more by this injection you may benefit from Radiofrequency Neurotomy, for longer term pain relief. If the relief is less than this amount, you may have other significant spine disease that should be addressed with other therapies.
What is a Medial Branch Block?
A medial branch block involves the x-ray guided injection of a medication onto the nerve to the z-joint. You will be placed face down on a soft table for the low back medial branch block and face down or on your side for the neck (cervical) medial branch blocks. After skin preparation, a small amount of local anesthesia is injected into the skin. IV sedation is usually not given as this is a diagnostic test whose outcome depends on your ability to perceive pain relief. A thin needle is guided onto the medial branch nerve and a small amount of iodinated x-ray dye is injected to assure proper placement, then a medication will be injected and the needle is removed. Usually 2-3 injections are required at the time of the procedure. After the injection, you will have your pain and function briefly assessed, then you will go home where you will continue to assess the outcome of the block over the next several hours. The time period for which relief is perceived and the degree of relief (pain scale or other) is important information that is used to direct further therapy.