Iliocostalis

The iliocostalis (Latin: musculus iliocostalis) is a deep back muscle that runs along the length of the spine and lies lateral to the longissimus. It is one of the three muscles forming the erector spinae muscle complex - the most powerful extensor of the back. Besides the iliocostalis, the erector spinae is also formed by the longissimus and spinalis muscles. The erector spinae muscles lie in the intermediate layer of the deep back muscles. The iliocostalis muscle has three parts according to their origin - iliocostalis cervicis, iliocostalis thoracis and iliocostalis lumborum.

Iliocostalis cervicis

Iliocostalis cervicis
Origin3rd - 6th rib angles
InsertionTransverse processes of C4 - C6 vertebrae
Action

Bilateral contractions - extension of cervical spine

Unilateral contractions - ipsilateral lateral flexion of cervical spine

InnervationLateral branches of dorsal rami of cervical spinal nerves
Blood supplyVertebral, deep cervical and occipital arteries

Origin

The muscle fibers of the iliocostalis cervicis originate from the third to sixth rib angles.

Insertion

The iliocostalis cervicis inserts on the transverse processes of the fourth to sixth cervical vertebrae (C4 - C6).

Action

Muscle contractions on both sides (bilateral contractions) extend the cervical spine. Contractions on one side (unilateral contractions) provide lateral flexion of the cervical spine to the same side (ipsilateral). However, the iliocostalis cervicis is a muscle with very little force capacity.

Innervation

The iliocostalis cervicis is innervated by the lateral branches of the dorsal rami of the cervical spinal nerves.

Blood supply

The iliocostalis cervicis receives oxygenated blood via the occipital, deep cervical and vertebral arteries. The occipital artery is a branch of the external carotid artery, while the deep cervical artery arises from the costocervical trunk. And finally, the vertebral artery branches off the subclavian artery.

Iliocostalis thoracis

Iliocostalis thoracis
Origin7th - 12th rib angles
Insertion1st - 6th rib angles, transverse process of C7 vertebra
Action

Bilateral contractions - extension of thoracic spine

Unilateral contractions - ipsilateral lateral flexion of thoracic spine

InnervationLateral branches of dorsal rami of thoracic spinal nerves
Blood supplyDorsal branches of posterior intercostal and subcostal arteries

Origin

The iliocostalis thoracis muscle fibers originate from the seventh to twelfth rib angles.

Insertion

The iliocostalis thoracis inserts on the angles of the first to sixth ribs. Also, some fibers attach to the transverse process of the seventh cervical vertebra (C7).

Action

Muscle contractions on both sides (bilateral contractions) extend the thoracic spine. Contractions on one side (unilateral contractions) provide lateral flexion of the thoracic spine to the same side (ipsilateral).

Innervation

The iliocostalis cervicis muscle is innervated by the lateral branches of the dorsal rami of the thoracic spinal nerves.

Blood supply

The iliocostalis thoracis is supplied by the dorsal branches of the posterior intercostal and subcostal arteries. The posterior intercostal arteries arise from the superior intercostal arteries and thoracic aorta. The subcostal artery is a branch of the thoracic aorta.

Iliocostalis lumborum

Iliocostalis lumborum
OriginLateral crest of sacrum, medial aspect of iliac crest, thoracolumbar fascia
Insertion5th - 12th rib angles, transverse processes of L1 - L4 vertebra, adjacent thoracolumbar fascia
Action

Bilateral contractions - extension of lumbar spine

Unilateral contractions - ipsilateral lateral flexion of lumbar spine

InnervationLateral branches of dorsal rami of lumbar spinal nerves
Blood supplyBranches of lumbar and lateral sacral arteries

Origin

The iliocostalis lumborum arises from the lateral crest of the sacrum, medial aspect of the iliac crest and the thoracolumbar fascia.

Insertion

The iliocostalis lumborum muscle inserts on the fifth to twelfth rib angles, transverse processes of the first to fourth lumbar vertebrae (L1 - L4) and the adjacent thoracolumbar fascia.

Action

Muscle contractions on both sides (bilateral contractions) extend the lumbar spine. Contractions on one side (unilateral contractions) provide lateral flexion of the lumbar spine to the same side (ipsilateral).

Innervation

The iliocostalis cervicis is innervated by the lateral branches of the dorsal rami of the lumbar spinal nerves.

Blood supply

The iliocostalis lumborum receives arterial blood supply from the dorsal branches of the lumbar and lateral sacral arteries. The lumbar arteries are branches of the abdominal aorta, while the lateral sacral arteries arise from the internal iliac arteries.