Iliocostalis thoracis is the thoracic segment of the lateral erector spinae column, bridging the lower six ribs to the upper six ribs and C7. It is the thoracic component responsible for the lateral thoracic extension force that maintains thoracic kyphosis control.
| Origin | Superior borders of ribs 7-12 — medial to the angles |
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| Insertion | Transverse processes of C7 and superior borders of ribs 1-6 |
| Nerve Supply | Dorsal rami of thoracic spinal nerves (T1-T12) |
| Blood Supply | Posterior intercostal arteries |
| Actions | Extends the thoracic spine; Ipsilateral lateral thoracic flexion; Depresses the upper ribs during expiration |
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Iliocostalis thoracis is the paraspinal muscle column most affected by scoliosis — asymmetric iliocostalis thoracis bulk on the convex versus concave sides of the scoliotic curve is used as a surgical landmark for curve level identification. Its denervation during thoracic spine surgery from dorsal rami injury contributes to post-operative thoracic paraspinal atrophy.
Palpated as the lateral thoracic paraspinal muscle mass during resisted trunk extension.
Asymmetric iliocostalis thoracis bulk between the convex and concave sides of a thoracic scoliotic curve, identified at surgery as a reference for the rotational apex level.
