For the facet joints, the medial branch nerves are the small nerves that carry pain signals to the brain.

Facet joints are pairs of small joints that are situated at each vertebral level of the spine. A facet joint may also be called a zygapophysial joint or a Z-joint.

See Facet Joint Disorders and Back Pain

Medial Nerves

Each facet joint is connected to two medial nerves that carry pain signals away from the spine to the brain.


The medial nerves are uniquely located in each segment of the spine:

  • Cervical medial branch nerves are located in a bony groove in the neck
  • Thoracic medial branch nerves are located over a bone in the mid-back or upper back
  • Lumbosacral medial branch nerves are found in a bony groove in the low back

    See Spinal Cord and Spinal Nerve Roots

Medial Nerve Function

The medial branch nerve block is designed to interrupt the nerves ability to transmit the pain signals to the brain, which in turn will determine - or diagnose - if the facet joint(s) is the source of the patient's pain.

These medial branch nerves do not control any major muscles or carry any sensation in the arms or legs, so there is no danger of negatively affecting those areas - or negatively affecting other pain sensing processes - with a medial branch block.

The medial branch nerves do control small muscles in the neck, the mid and lower back, but loss of these nerves has not proved harmful.

Dr. Ray Baker is an anesthesiologist specializing in interventional pain medicine and non-surgical spine care. He has more than 25 years of clinical experience serving on staff in hospitals and medical centers in Washington state.

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