The thoracic dorsal (posterior) rami arise from each thoracic spinal nerve just outside the intervertebral foramen and divide into medial and lateral branches. The medial branches supply the deep paraspinal muscles (multifidus, rotatores, semispinalis) and carry cutaneous sensation to the posterior midline thoracic skin. The lateral branches supply the iliocostalis and longissimus muscles and carry cutaneous sensation to the lateral back skin. The T1-T6 medial branches are primarily cutaneous; T7-T12 medial branches are primarily muscular.
Thoracic dorsal ramus syndrome produces localised thoracic facet joint pain that radiates along the dorsal ramus distribution into the posterior thorax, mimicking referred visceral pain. The thoracic facet joint and dorsal ramus medial branch are targeted in medial branch nerve blocks and radiofrequency ablation for chronic thoracic facet joint pain. Posterior ramus entrapment by thoracic fascial bands at the thoracolumbar junction (T11-L2) causes lateral cutaneous nerve entrapment producing a burning lateral trunk pain known as iliocostal friction syndrome or Maigne syndrome.
Irritation of the thoracic medial branch dorsal rami from thoracic facet joint arthrosis or synovial cyst produces a unilateral paravertebral aching pain that radiates in a dorsal ramus cutaneous pattern, treated by medial branch block at the thoracic facet and, for persistent pain, radiofrequency denervation.
Entrapment of the T11-L2 dorsal rami lateral branches at the thoracolumbar junction produces a burning lateral trunk and iliac crest pain that mimics hip pathology, diagnosed by reproduction of pain on lateral vertebral pressure at the junction and relieved by local anaesthetic injection.
