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Iliocostalis Muscle Anatomy

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Origin
  • Iliocostalis cervicis: angles of ribs 3-6
  • Iliocostalis thoracis: angles of ribs 7-12
  • Iliocostalis lumborum: medial end of the iliac crest, lateral crest of the sacrum, and thoracolumbar fascia
Insertion
  • Iliocostalis cervicis: posterior tubercles of the transverse processes of C4-C6
  • Iliocostalis thoracis: transverse process of C7 and angles of ribs 1-6
  • Iliocostalis lumborum: transverse processes of L1-L4 and angles of ribs 4-12
Action
  • Unilateral contraction: lateral flexion of the trunk/vertebral column and weak lateral flexion at the base of the neck (below C4)
  • Bilateral contraction: extends the trunk/vertebral column and weakly assists extension of the base of the neck (below C4)
Innervation
  • Lateral branches of the posterior rami of the spinal nerves
Blood Supply
  • Dorsal branches of segmental arteries, including posterior intercostal, subcostal, lumbar, and lateral sacral arteries
Last updated: Estimated Reading Time: 9 min

Location & Overview

The iliocostalis muscle is part of the deep musculature of the back and one of the three muscles that make up the erector spinae group, alongside the spinalis and longissimus. Of these three, the iliocostalis is the most lateral. The iliocostalis is separated into three distinct regions: iliocostalis cervicis, iliocostalis thoracis, and iliocostalis lumborum. The iliocostalis lumborum is the most inferior section, the iliocostalis thoracis is in the middle, and the iliocostalis cervicis is the most superior section. The different sections are displayed in the images below.[1,2]

The iliocostalis muscle plays an important role in various sporting activities, such as powerlifting, where it helps to maintain spinal extension during competition lifts like the deadlift. It also aids in stabilizing and supporting the spine during gymnastics movements. In swimming, it helps to maintain proper body position, especially during freestyle and backstroke. The iliocostalis muscle is also important for day-to-day activities, such as lifting objects, by stabilizing the spine and maintaining proper posture. It also assists with less strenuous tasks, such as sitting upright and standing upright.

iliocostalis muscle
Pictured here, we can see the iliocostalis muscle by itself. The iliocostalis is the most lateral of the erector spinae muscles.
iliocostalis muscle sections - iliocostalis lumborum, iliocostalis thoracis, iliocostalis cervicis
This image shows the different sections of the iliocostalis muscle. The cervicis is highlighted in yellow, the thoracis in purple, and the lumborum in green.
erector spinae muscles together
Displayed here are all of the erector spinae muscles together.
erector spinae muscle with the iliocostalis, longissimus and spinalis labeled
Pictured here, we can see the erector spinae muscle group. The spinalis is highlighted in yellow, the longissimus in purple, and the iliocostalis in green.

Origin & Insertion

The points of origin and insertion of the iliocostalis muscle differ among its various segments. The specifics are as follows:

The iliocostalis cervicis has its origin at the angles of ribs 3 to 6 and inserts at the posterior tubercles of the transverse processes of vertebrae C4 to C6.[1,2]

iliocostalis cervicis origin and insertion
Displayed in this picture are the origins and insertions of the iliocostalis cervicis section, with origins highlighted in red and insertions highlighted in blue.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.

The iliocostalis thoracis originates at the angles of the lower six ribs and inserts at the transverse process of vertebra C7 and the angles of the upper six ribs.[1,2]

iliocostalis thoracis origin and insertion
This image displays the origins and insertions of the iliocostalis thoracis section, with the origins highlighted in red and the insertions highlighted in blue.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.

The iliocostalis lumborum originates at the medial end and dorsal segment of the iliac crest, the lateral crest of the sacrum, and the thoracolumbar fascia. It inserts at the lumbar transverse processes of L1 to L4 and the angles of ribs 4 to 12.[1,2]

iliocostalis lumborum origin and insertion
This image presents the origins and insertions of the iliocostalis lumborum section, with the origins highlighted in red and the insertions in blue.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.
thoracolumbar fascia
Pictured here, we can see the thoracolumbar fascia, another origin point of the iliocostalis lumborum. Due to the location of its attachments, some people also consider the thoracolumbar fascia to be an insertion point as well. The classification of whether the thoracolumbar fascia is an origin or insertion point of the iliocostalis lumborum appears to vary among individuals and sources. However, it is most commonly considered an origin.
Origins and insertions of iliocostalis lumborum, thoracis, and cervicis
Pictured here are the origins and insertions of the iliocostalis lumborum, thoracis, and cervicis, with origins highlighted in red and insertions in blue. The cervicis has a yellow highlight around it, the thoracis has a purple highlight, and the lumborum has a green highlight.
Note: For the sake of simplicity, only the left side of the muscle is displayed here. However, the origins and insertions are duplicated on the right-hand side as well.

Action & Function

The actions of the iliocostalis muscle vary based on whether it contracts unilaterally or bilaterally. When only one side contracts, the result is lateral flexion of the trunk and vertebral column. When both sides contract together, it causes extension of the trunk and vertebral column. The cervicis segment of the muscle extends from the cervical vertebrae to the fourth cervical vertebra (C4), it contributes weakly to lateral flexion at the base of the neck during unilateral contraction and weakly assists extension at the base of the neck during bilateral contraction.[3,2]

Image of a person demonstrating the movement of trunk extension.
This image shows an example of trunk extension, which involves arching or bending the spine/torso backward. The opposite of trunk extension is trunk flexion. The iliocostalis lumborum and thoracis sections are involved in trunk extension. This extension is the result of a bilateral contraction.
Image of a person demonstrating the movement of trunk lateral flexion.
This image demonstrates trunk lateral flexion, which involves bending the torso to the side. The iliocostalis lumborum and thoracis sections are involved in trunk lateral flexion. This lateral flexion is the result of a unilateral contraction.
Image of a person demonstrating the movement of neck extension.
This image demonstrates neck extension, which involves bending the neck backward. The iliocostalis cervicis section is involved in neck extension at the base of the neck. This extension is the result of a bilateral contraction. It provides other muscles with weak assistance with extension because it is not a strong extender of the neck.
Image of a person demonstrating the movement of neck lateral flexion.
This image demonstrates neck lateral flexion, which involves bending the neck to the side. The iliocostalis cervicis section is involved in lateral flexion at the base of the neck. This lateral flexion is the result of a unilateral contraction. It provides other muscles with weak assistance during lateral flexion because it is not a strong lateral flexor of the neck.

Innervation

The iliocostalis muscle is innervated by the lateral branches of the posterior rami of the spinal nerves, with each vertebral level corresponding to its own nerve supply.[3,2]

spinal nerves anatomy
Pictured here is a cross-section of a lumbar vertebra. One of the labeled parts is the ‘dorsal ramus’, which is also known as the ‘posterior ramus’. Each segment of the erector spinae muscles receives innervation from the posterior ramus of the corresponding spinal nerve. In other words, the part of the muscle aligned with a specific spinal segment is innervated by that specific spinal nerve’s posterior ramus.

Blood Supply

Blood is supplied to the iliocostalis mainly through dorsal branches of the segmental arteries that supply the deep muscles of the back. In the thoracic region, the dorsal branches of the posterior intercostal arteries divide into medial and lateral musculocutaneous branches. The lateral branches supply the iliocostalis, along with longissimus thoracis and nearby overlying tissues.[4]

Because the iliocostalis extends through cervical, thoracic, lumbar, and sacral regions, its arterial supply varies by level. Superiorly, the deep back muscles receive contributions from vessels such as the vertebral, deep cervical, occipital, and transverse cervical arteries. More inferiorly, they receive blood from dorsal branches of the posterior intercostal, subcostal, lumbar, and lateral sacral arteries. In practical terms, the iliocostalis is best understood as receiving a segmental blood supply from the vessels that serve the deep muscles of the back at each region of the spine.[4,5]

References

  1. [1] Henson B, Kadiyala B, Edens MA. Anatomy, Back, Muscles. (Updated 2022 Aug 25). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK537074/
  2. [2] Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2017.
  3. [3] Chaitow, Leon, and DeLany, Judith (2011), Clinical Application of Neuromuscular Techniques, Volume 2 (Second Edition), Oxford: Churchill Livingstone, ISBN 978-0-443-06815-7
  4. [4] Standring S, editor. Gray’s anatomy: the anatomical basis of clinical practice. 42nd ed. Amsterdam: Elsevier; 2021.
  5. [5] Dalley AF II, Agur AMR. Moore’s Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.

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