The anterior scalene is the most clinically significant scalene, forming the anterior boundary of the interscalene triangle through which the brachial plexus exits. The subclavian artery passes posterior to it and the subclavian vein anterior to it, making it the key landmark in thoracic outlet anatomy. Its attachment to the first rib via the scalene tubercle is the target of first rib resection for thoracic outlet syndrome, and anterior scalenectomy is the primary surgical procedure for neurogenic thoracic outlet syndrome.
| Origin | Anterior tubercles of the transverse processes of C3 through C6 |
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| Insertion | Scalene tubercle and superior surface of the first rib |
| Nerve Supply | Ventral rami of the cervical spinal nerves C4 through C6 |
| Blood Supply | Ascending cervical artery |
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Its first rib elevation during forced inspiration is mechanically important for maximising upper thoracic volume, but its clinical significance primarily relates to its boundary of the scalene triangle through which brachial plexus and subclavian artery compression occurs.
Anterior scalene hypertrophy, trigger points or fibrosis are a major contributor to neurogenic thoracic outlet syndrome, producing arm pain and paraesthesia that are provoked by overhead positions. Botulinum toxin injection into the muscle is used both to test and to treat this. Surgical decompression divides the muscle from its first rib insertion through a supraclavicular approach (scalenectomy), often with first rib resection. The phrenic nerve runs down its anterior surface and must be protected during this surgery, and it is often blocked unintentionally by an interscalene brachial plexus block, which is placed in the groove between the anterior and middle scalenes.
The anterior scalene is palpable as a firm cord running posterolateral to the sternocleidomastoid in the lower anterior neck, becoming firm during deep inspiration and resisted lateral neck flexion. Tinel sign over it may reproduce arm symptoms in thoracic outlet syndrome.
Brachial plexus compression by the anterior scalene muscle producing arm pain, weakness, and paraesthesia reproduced by overhead arm positions and the Adson test, managed with physiotherapy, botulinum toxin, or scalenectomy.
