The iliocostalis is a deep back muscle, one of the three muscles forming the erector spinae. It runs along the length of the spine and lies lateral to the longissimus. The erector spinae muscles lie in the intermediate layer of the deep back muscles.

According to its origin, the iliocostalis has three parts - iliocostalis cervicis, iliocostalis thoracis and iliocostalis lumborum. The primary function of the iliocostalis is to extend the spine during bilateral contractions and laterally flex the spine during unilateral contractions.

Iliocostalis cervicis

The iliocostalis cervicis is the first part of the iliocostalis muscles, and it stretches between the cervical vertebrae and rib angles.

Origin: third to sixth rib angles.

Insertion: transverse processes of the fourth to sixth cervical vertebrae (C4 - C6).

Action: bilateral contractions - extension of the cervical spine; unilateral contractions - lateral flexion of the cervical spine to the same side (ipsilateral). However, the iliocostalis cervicis is a muscle with very little force capacity.

Innervation: lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply: occipital, deep cervical and vertebral arteries.

Iliocostalis thoracis

The iliocostalis thoracis is the middle portion of the iliocostalis muscles, and it stretches between the rib angles and the seventh cervical vertebra (C7).

Origin: seventh to twelfth rib angles.

Insertion: first to sixth rib angles, transverse process of the seventh cervical vertebra (C7).

Action: bilateral contractions - extension of the thoracic spine; unilateral contractions - lateral flexion of the thoracic spine to the same side (ipsilateral).

Innervation: lateral branches of the dorsal rami of the thoracic spinal nerves.

Blood supply: dorsal branches of the posterior intercostal and subcostal arteries.

Iliocostalis lumborum

The iliocostalis lumborum is the most caudal portion of the iliocostalis, and it extends between the sacrum, ilium, thoracolumbar fascia, rib angles and lumbar vertebrae.

Origin: lateral crest of the sacrum, medial end of the iliac crest and thoracolumbar fascia.

Insertion: fifth to twelfth rib angles, transverse processes of vertebrae L1 to L4, thoracolumbar fascia.

Action: bilateral contractions - extension of the lumbar spine; unilateral contractions - lateral flexion of the lumbar spine to the same side (ipsilateral).

Innervation: lateral branches of the dorsal rami of the lumbar spinal nerves.

Blood supply: dorsal branches of the lumbar and lateral sacral arteries.

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Iliocostalis muscle