The thoracic iliocostalis runs rib-to-rib in the thoracic region, extending and stabilising the thoracic spine while also stabilising the rib cage during high-demand breathing. It is the most lateral component of the erector spinae in the thorax. Thoracic erector spinae tightness from prolonged sitting is a significant contributor to the hyperkyphosis posture of desk workers.
| Origin | Angles of ribs 7 through 12 |
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| Insertion | Angles of ribs 1 through 6 and transverse process of C7 |
| Nerve Supply | Posterior rami of thoracic spinal nerves |
| Blood Supply | Posterior intercostal arteries |
| Actions | Extension of the thoracic spine; Ipsilateral lateral flexion of the thoracic spine; Stabilises the rib cage during forced breathing |
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By connecting adjacent ribs laterally it resists excessive thoracic kyphosis during loaded activities and stabilises the rib cage against the respiratory demands of strenuous exercise.
Thoracic erector spinae strains are common from sudden trunk rotation under load. The thoracic region of the iliocostalis is less commonly treated in isolation than the lumbar portion but contributes significantly to mid-back pain patterns in rowers and golfers.
Palpable as the most lateral erector spinae band in the thoracic region, lateral to the longissimus thoracis.
Iliocostalis thoracis injury from rotation under load producing thoracic back pain, managed with early mobilisation and graduated loading.
