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Scalene Muscles Anatomy

Last updated on: November 30, 2024

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The scalene muscles group consists of three paired muscles: the anterior scalene (scalenus anterior), middle scalene (scalenus medius), and posterior scalene (scalenus posterior). These muscles originate from the transverse processes of the cervical vertebrae and insert into the first and second ribs, forming a sophisticated biomechanical system that influences both cervical and thoracic function.

Scalene Muscles Anatomy

Anterior Scalene (Scalenus Anterior)

The anterior scalene originates from the anterior tubercles of the transverse processes of C3-C6 vertebrae. Its insertion point is at the scalene tubercle on the inner border of the first rib. This muscle serves as a critical anatomical landmark, as it forms the anterior border of the interscalene triangle, through which the brachial plexus and subclavian artery pass. The phrenic nerve descends vertically on its anterior surface, making this muscle particularly significant in surgical approaches to the cervical region.

See Also: Brachial Plexus Anatomy

Middle Scalene (Scalenus Medius)

The middle scalene, typically the largest of the scalene muscles, originates from the posterior tubercles of the transverse processes of C2-C7 vertebrae. It inserts into the upper surface of the first rib, posterior to the groove for the subclavian artery. This muscle forms the posterior border of the interscalene triangle and plays a crucial role in cervical spine stabilization during rotational movements.

Posterior Scalene (Scalenus Posterior)

The posterior scalene, often the smallest of the three scalene muscles, originates from the posterior tubercles of C4-C6 vertebrae and inserts into the external border of the second rib. While less clinically significant than its anterior and middle counterparts, it contributes to cervical spine stability and respiratory mechanics.

The scalene muscles have intricate relationships with crucial neurovascular structures. The brachial plexus and subclavian artery pass between the anterior and middle scalene muscles, while the subclavian vein typically passes anterior to the anterior scalene. This anatomical arrangement creates potential sites for neurovascular compression, particularly in thoracic outlet syndrome. The phrenic nerve’s course along the anterior scalene’s surface adds another layer of clinical significance, especially during surgical procedures in this region.

Origin	Anterior scalene muscle: anterior tubercle of transverse processes of vertebrae C3-C6 Middle scalene muscle: posterior tubercles of transverse processes of vertebrae C2-C7 Posterior scalene muscle: posterior tubercles of transverse processes of vertebrae C5-C7
Insertion	Anterior scalene muscle: anterior scalene tubercle of rib 1, superior border of rib 1 (anterior to subclavian groove) Middle scalene muscle: superior border of rib 1 (posterior to subclavian groove) Posterior scalene muscle: external surface of rib 2
Innervation	Anterior scalene muscle: anterior rami of spinal nerves C4-C6 Middle scalene muscle: anterior rami of spinal nerves C3-C8 Posterior scalene muscle: anterior rami of spinal nerves C6-C8
Blood Supply	All are supplied by the ascending cervical branch of the inferior thyroid artery.
Action	Anterior scalene muscle: bilateral contraction: neck flexion. Unilateral contraction: neck lateral flexion (ipsilateral), neck rotation (contralateral), elevates rib 1. Middle scalene muscle: neck lateral flexion, elevates rib 1. Posterior scalene muscle: neck lateral flexion, Elevates rib 2.

Clinical Significance

Scalene muscles dysfunction can manifest as neck pain, upper extremity symptoms, or respiratory complications. The muscles may become hyperactive or shortened in various clinical conditions, including chronic neck pain, forward head posture, and respiratory distress. Their anatomical relationship with the brachial plexus and subclavian vessels makes them potential sources of neurovascular compression syndromes.

References & More

Clinically Oriented Anatomy – 8th Edition
Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 42nd Edition https://www.elsevier.com/books/grays-anatomy/standring/978-0-7020-7710-5
Bordoni B, Varacallo M. Anatomy, Head and Neck, Scalenus Muscle. 2023 Apr 10. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan–. PMID: 30085600. Pubmed