Iliocostalis Muscle Anatomy

The iliocostalis muscle forms the lateral portion of the sacrospinalis muscle complex, extending along the vertebral column from the sacrum to the cervical region.
Iliocostalis Muscle Anatomy
The Iliocostalis muscle demonstrates a complex architectural arrangement, divided into three distinct segments: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis, each serving specific functional roles in spinal biomechanics.
Origin & Insertion
The iliocostalis lumborum originates from the broad tendon attached to the posterior surface of the sacrum, the posterior superior iliac spine, and the supraspinous ligaments of the lumbar vertebrae. Its muscle fibers course superiorly, inserting into the inferior borders of the angles of the lower six or seven ribs.
The iliocostalis thoracis demonstrates attachment points from the angles of the lower six ribs, with insertions into the angles of the upper six ribs and the posterior tubercle of the transverse process of C7. This segmental arrangement provides crucial stability during respiratory movements and trunk rotation.
The iliocostalis cervicis, the most superior component, originates from the angles of ribs 3-6 and inserts into the posterior tubercles of the transverse processes of C4-C6 vertebrae. This arrangement facilitates cervical extension and lateral flexion movements.

Neurovascular Supply
The neurovascular supply of the iliocostalis muscle complex derives from multiple segmental sources, reflecting its extensive anatomical distribution. Primary innervation occurs through the lateral branches of posterior rami of spinal nerves, with each segment receiving innervation from multiple levels ensuring redundancy in neural control.
The arterial supply primarily comes from the posterior branches of the intercostal and lumbar arteries, forming a complex anastomotic network that ensures adequate perfusion during various postural demands, where the Iliocostalis cervicis is supplied by the occipital, deep cervical and vertebral arteries, the Iliocostalis thoracis is supplied by the dorsal branches of posterior intercostal and subcostal arteries and the Iliocostalis lumborum is supplied by the dorsal branches of lumbar and lateral sacral arteries.
Functional Significance
When acting bilaterally, these muscles function as powerful extensors of the vertebral column, crucial for maintaining erect posture and controlling forward bending movements. Unilateral contraction facilitates lateral flexion and rotation of the trunk, contributing to complex movement patterns in daily activities.
See Also: Cervical Spine Range of Motion
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) |
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 |
Action | Bilateral contraction: Extension of spine Unilateral contraction: Lateral flexion of spine (ipsilateral) |
Clinical Implications
Medical professionals frequently encounter pathologies involving the iliocostalis muscle in clinical practice. Acute strain patterns typically present with localized pain and reduced range of motion, while chronic conditions may manifest as part of broader myofascial pain syndromes. Detailed knowledge of the muscle’s anatomical relationships aids in differential diagnosis and treatment planning.
Modern imaging techniques, including magnetic resonance imaging and ultrasound, have enhanced our ability to visualize iliocostalis muscle pathology. These modalities prove particularly valuable in identifying structural changes, such as fatty infiltration or atrophy, which may indicate chronic pathology or denervation.
References & More
- Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 42nd Edition https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-7710-5
- Journal of Anatomy: “The architecture of the connective tissue in the musculoskeletal system” https://www.ncbi.nlm.nih.gov/pmc/journals/241/
- Clinical Anatomy: “Variations in the anatomical arrangements of the erector spinae muscle group” https://onlinelibrary.wiley.com/journal/10982353
- Spine Journal: “Biomechanical analysis of the erector spinae muscles in various loading conditions” https://www.thespinejournalonline.com/
- Atlas of Human Anatomy, 7th Edition, Frank H. Netter https://www.us.elsevierhealth.com/netters-atlas-of-human-anatomy-9780323393225.html
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