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.
| Origin | Thoracic spinal nerves T1-T12, just lateral to the intervertebral foramen |
|---|---|
| Course | Pass posteriorly medial to the superior costotransverse ligament and divide into medial and lateral branches that supply the back muscles and overlying skin |
| Motor |
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| Sensory |
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Irritation of the thoracic dorsal rami from facet joint arthrosis produces localised paravertebral pain that can radiate around the posterior thorax and mimic visceral pain. The medial branches, which cross the transverse processes, are the targets for thoracic medial branch blocks and radiofrequency ablation; good relief from two separate diagnostic blocks confirms the facet joint as the pain source before ablation. At the thoracolumbar junction (T11-L2), irritation of the dorsal rami causes low back and iliac crest pain that can mimic hip or lumbar disease (Maigne or thoracolumbar junction syndrome). The rami are also at risk during posterior thoracic instrumentation.
Facet joint arthrosis or a synovial cyst irritates the medial branch, producing one-sided paravertebral aching pain in a dorsal ramus pattern, treated by medial branch block and, if pain persists, radiofrequency denervation.
Irritation of the T11-L2 dorsal rami at the thoracolumbar junction causes low back, buttock and iliac crest pain that mimics hip or lumbar disease, reproduced by pressure at the junction and relieved by local anaesthetic injection.
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