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Scalene Muscles – Functional Anatomy

Scalenes are 3 (sometimes 4) muscles on either side of the neck. The three bellies are named for their position; scalenus anterior, scalenus medius, scalenus posterior. The anomalous belly is called scalenus minimus.
They are lateral cervical muscles that connect the cervical vertebrae to the upper thoracic cage. They are long muscles with fibers of uneven length.
Scalenus anterior lies almost entirely under the clavicular head of sternocleidomastoid in the pedicle groove. It passes anterior to the cervical nerves and subclavian artery but behind the subclavian vein.
Scalenus posterior lies mostly under the anterior border of the trapezius. It passes posterior to the cervical nerves and the subclavian artery.
Scalenus medius lies in the posterior cervical triangle between the other two scalenes.

They vary in their attachments and size a great deal of the time (about 40-71% of the reviewed studies).

Anatomy

Scalenus anterior

Scalenus anterior originates from a flat tendon on the first rib just under the clavicular SCM, medial to the thoracic bundle. It inserts along the anterior tubercles on the transverse process of C3-C6. The upper attachment on C3 is usually a more prominent tubercle than the other cervical vertebrae and easily distinguished with palpation.

There are reports of it extending to attach to the second rib as well.

Scalenus, minimus

Dissection information on the scalenus minimus is highly variable. It is reported from 7-71% of the time and varies in its attachments.

Scalenus minimus is the most variable of the scalene muscles. It originates from the fascia of the thoracic pleura and sometimes the first rib. It inserts on the posterior tubercle of C7, sometimes C6. It passes posterior to the subclavian artery.

Scalenus medius

Scalenus medius originates from a flat tendon on the 1st rib just lateral to the thoracic neurovascular bundle. It inserts on the posterior tubercles of the transverse processes of C2-C7. This traps C7-T1 between origin and insertion.

Scalenus posterior

Scalenus posterior originates from a flat tendon on lateral aspect of the 2nd rib. It inserts on the posterior tubercles of the C4-C6 or C7. 

This traps T1 andT2 between the bones of origin and insertion.

Scalenus posterior has very similar attachments to iliocostalis cervicis and serratus posterior superior. They pull on the same structures and synergize closely. They are an important part of resolving forward head posture and lateral flexion of the lower cervicals.

Function

Scalenes draw the cervical vertebrae toward the upper ribs. The implications of this can be complicated and argued at length.

  • Contraction creates lateral flexion of the neck when the ribs are fixed.
  • Contraction lifts the thoracic cage when the neck is fixed.

Lifting Ribs to Breathe

During inhalation, especially when the trunk is flexed, scalenes lift the upper ribs from a fixed vertebral column to create volume in the chest cavity. Depending on position and trigger point activity, the scalene muscles synergize with sternocleidomastoid, iliocostalis cervicis, and serratus posterior superior. Trapezius and levator scapula support the pectoral girdle so that the serratus anterior and pectoralis minor can also assist.

Scalenus anterior is a poor flexor of the neck but does become chronically shortened in Forward-Head Posture. This is complemented on the Back of the upper neck by the short extensors of the head; sub-occipitals, splenius capitis, and semispinalis capitis. After the more superficial phasic muscles are released, the deep tonic muscles still hold the Pattern of Forward-Head Posture.

Scalenus posterior has very similar attachments to iliocostalis cervicis and serratus posterior superior. They pull on the same structures and synergize closely. They are an important part of resolving forward head posture and lateral flexion of the lower cervical vertebrae.

Lateral Flexion and Rotation

When the ribs are stabilized, and the vertebrae are allowed to move, they laterally flex the neck. They synergize with the sternocleidomastoid, lower sections of the levator scapula, and upper trapezius.

Anatomy books are confusing and contradictory about the role that scalenes play in the rotation of the vertebrae. No electro-myographical studies were found to support these claims. That being said, scalene referral patterns can be more easily elicited when the head is rotated ipsilaterally while laterally flexing toward the opposite shoulder.

Helpful Collections

Thoracic Outlet Syndrome

Scalenes are a key part of thoracic outlet syndrome. They entrap nerves and blood vessels as they pass into the upper extremity. Also, They create patterns of pain, restriction, and swelling in the arm.

This collection contains posts about the thoracic outlet including:

  • involved muscles
  • pain patterns
  • exercises
  • anatomy and physiology

Torso Into Arm

Scalene muscles are often suspected when pain occurs in the arm and hand. This is both useful and confusing. Many referral patterns overlap scalene referral patterns. It leads the novice therapist to treat scalenes too often.

This Collection contains posts about trigger points that refer from the torso into the arm. It can be a helpful quick reference for comparing patterns and sorting out the real problem.

Consider the Supporting Muscles

This muscle contributes to Forward-Head posture. It becomes short and strong. Once the head has become imbalanced over the trunk, this muscle is supported to become shorter and stronger.

If you have Forward-Head Posture, review this collection, especially the self-care exercise Tuck, Tilt, Turn and Lift.

Wikipedia entry for scalene muscles

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Tony Preston has a practice in Atlanta, Georgia, where he sees clients. He has written and taught about anatomy, trigger points, and cranial therapies since the mid-90s.

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*This site is undergoing significant changes. We are reformatting and expanding the posts to make them easier to read. The result will also be more accessible and will include more patterns with better self-care. In the meanwhile, there may be inconsistencies in formatting, content presentation, and readability. Until we get older posts updated, please excuse our mess.