The iliocostalis is the most lateral column of the erector spinae, running from the iliac crest to the rib angles and cervical transverse processes. It is a gross mover rather than a segmental stabiliser, producing lateral trunk flexion and extension. Iliocostalis strains from deadlifting and heavy manual work produce the 'back-out' lateral low back pain.
| Origin | Lumborum: iliac crest and thoracolumbar fascia. Thoracis: lower six rib angles. Cervicis: upper six rib angles |
|---|---|
| Insertion | Lumborum: rib angles 5-12. Thoracis: rib angles 1-6 and C7 transverse process. Cervicis: C4-C6 transverse processes |
| Nerve Supply | Dorsal rami of spinal nerves at each level |
| Blood Supply | Posterior intercostal and lumbar arteries |
| Actions | Bilateral: spinal extension (the most lateral erector — produces extension with a lateral shear component); Unilateral: ipsilateral lateral flexion |
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Erector spinae plane block (ESPB) targets the plane between the erector spinae and the transverse process tip — the iliocostalis is the most posterior layer of the erector group and the primary muscle infiltrated in this regional anaesthesia technique for thoracic and abdominal surgery.
The iliocostalis forms the lateral column of the palpable paraspinal mass, identifiable by its attachment to the rib angles during lateral palpation of the thoracic and lumbar back.
Iliocostalis overload from heavy lifting producing acute lateral low back pain managed with analgesia, progressive loading, and ergonomic correction.
