Iliocostalis is a deep back muscle that together with the longissimus and spinalis muscles comprises the erector spinae muscle group. These three muscles of erector spinae are arranged into longitudinal cords, with iliocostalis composing the lateral and longissimus and spinalis making up the intermediate and medial cords, respectively. Iliocostalis is horizontally divided into three regional parts according to their origin; iliocostalis cervicis, iliocostalis thoracis and iliocostalis lumborum.
Being a part of the most powerful extensor of the back, the function of iliocostalis muscle is to extend the spine when contracting bilaterally and to laterally flex the spine when contracting unilaterally.
|Origin||Iliocostalis cervicis: Angle of ribs 3-6
Iliocostalis thoracis: Angle of ribs 7-12
Iliocostalis lumborum: Lateral crest of sacrum, medial end of iliac crest, thoracolumbar fascia
|Insertion||Iliocostalis cervicis: Transverse processes of vertebrae C4-C6
Iliocostalis thoracis: Angles of ribs 1-6, transverse process of vertebra C7
Iliocostalis lumborum: Angle of ribs 5-12, transverse processes of vertebrae L1-L4 (+ Adjacent thoracolumbar fascia)
|Action||Bilateral contraction: Extension of spine
Unilateral contraction: Lateral flexion of spine (ipsilateral)
|Innervation||Lateral branches of posterior rami of spinal nerves|
|Blood supply||Iliocostalis cervicis: occipital, deep cervical and vertebral arteries
Iliocostalis thoracis: dorsal branches of posterior intercostal and subcostal arteries
Iliocostalis lumborum: dorsal branches of lumbar and lateral sacral arteries
This article will discuss the anatomy and function of the iliocostalis muscle.
Origin and insertion
Iliocostalis muscle spans the entire back, from the neck to the pelvis. Depending on which region of the back the parts of iliocostalis attach, the muscle is divided into cervical, thoracic and lumbar portions.
- Iliocostalis cervicis arises from the angles of ribs 3-6 and inserts to the transverse processes of vertebrae C4-C6.
- Iliocostalis thoracis originates from the angles of ribs 7-12 and inserts to the angles of the upper six ribs and transverse process of vertebra C7.
- Iliocostalis lumborum is divided into lumbar and thoracic parts.
The lumbar part of iliocostalis lumborum originates from the lateral crest of sacrum, medial end of iliac crest and thoracolumbar fascia. It courses superiorly and inserts to the transverse processes of vertebrae L1-L4 and to the adjacent part of the middle layer of thoracolumbar fascia. The muscle fibers are laminated so that those attaching to L1 are the most superficial and medial, while those inserting to L1 are the deepest and most lateral.
The thoracic part of iliocostalis lumborum originates from the same site as the lumbar, in a form of an aponeurotic sheath covering the lumbar part. Fibers course superiorly over the back and insert to the angle of ribs 5-12, laterally to iliocostalis thoracis. The muscle fibers of thoracic part are serially aligned, so that those attaching to the fifth rib are the most medial and inferior, while those inserting to the twelfth rib are the most lateral and superior.
Iliocostalis muscle lies over the posterior surface of the thoracic cage, in a gap between the longissimus muscle medially, and an imaginary line extending through the medial edge of scapula laterally.
The dorsal surface of its cervical part is covered by the splenius capitis and rhomboid muscles, while the thoracic and lumbar segments lie beneath the thoracolumbar fascia. Moreover, the superior and inferior portions of the thoracic part lie deep to the serratus posterior superior and inferior muscles, respectively.
Iliocostalis muscle is innervated by the lateral branches of posterior rami of cervical, thoracic and lumbar spinal nerves.
Arterial supply to iliocostalis has regional systematization;
Iliocostalis muscle acts in synergy with the two other erector spinae components (longissimus and spinalis) to produce movements of the vertebral column. When these muscles contract unilaterally, they produce ipsilateral lateral flexion of the spine, while when acting bilaterally, they extend the spine.
Lateral flexion and extension are the movements produced during concentric contraction of erector spinae. During forward flexion of the spine, erector spinae muscles eccentrically contract to smoothen the bending of the vertebral column.