The scalenes are a group of three muscles on the lateral neck connecting the cervical transverse processes to the upper two ribs. They are the primary muscles elevating the first and second ribs during forced or deep inhalation, but are also important cervical stabilisers and movers. The brachial plexus and subclavian artery pass between the anterior and middle scalenes in the scalene triangle, making this the most common site of thoracic outlet syndrome.
| Origin | Anterior tubercles of the transverse processes of C3 through C6; Posterior tubercles of the transverse processes of C2 through C7; Posterior tubercles of the transverse processes of C5 through C7 |
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| Insertion | Superior surface of the first rib; Outer surface of the second rib |
| Nerve Supply | Anterior rami of cervical spinal nerves C3 through C8 |
| Blood Supply | Ascending cervical artery; Subclavian artery |
| Actions | Elevation of the first and second ribs during forced inspiration; Ipsilateral lateral flexion of the cervical spine; Contralateral rotation of the cervical spine; Flexion of the lower cervical spine when acting bilaterally |
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They act as accessory breathing muscles that lift the upper ribs during any respiratory demand beyond quiet tidal breathing, becoming chronically overactive in people with breathing pattern disorders who use the upper chest rather than the diaphragm as their primary breathing muscle.
Scalene tightness and hypertrophy can compress the brachial plexus and subclavian artery in the scalene triangle, producing neurogenic or vascular thoracic outlet syndrome with arm pain, paraesthesia, and weakness that is reproduced by the elevated arm stress test. Scalene trigger points refer pain to the anterior chest, the upper limb, and the medial scapular border in patterns that closely mimic cardiac, cervical disc, and shoulder pathology. The phrenic nerve runs on the anterior surface of the anterior scalene and can be affected by scalene pathology.
The scalenes are palpable on the lateral neck just posterior to the sternocleidomastoid, becoming firm during deep inhalation or resisted cervical lateral flexion. Direct pressure into the scalene triangle between SCM and trapezius at the lower neck reproduces symptoms in thoracic outlet syndrome.
Compression of the brachial plexus or subclavian artery between the anterior and middle scalenes producing arm pain, paraesthesia, and weakness reproduced by overhead arm positions and relieved by lowering the arm.
Trigger points producing anterior chest, shoulder, and medial scapular pain patterns that closely mimic cardiac and disc pathology, managed with dry needling, breathing retraining, and postural correction.
