Middle Scalene Muscle

Description

Prominently rendered on the lateral neck, the middle scalene muscle (scalenus medius) rises from the posterior tubercles of the transverse processes of C2 through C7 and descends inferolaterally to its insertion on the superior surface of the first rib, posterior to the subclavian groove. Anterior to it, the sternocleidomastoid forms a superficial strap, while the anterior scalene lies more anteromedially, creating the interscalene interval between the two muscles. Superiorly, the posterior triangle musculature blends into the levator scapulae and the upper fibers of trapezius, and inferiorly the muscle approaches the clavicle, first rib, and apex of the thorax. Striations and fiber direction are clear. This perspective matters because the middle scalene is a primary landmark for the brachial plexus, whose roots and trunks course between the anterior and middle scalene, while the subclavian artery passes through the same space and the subclavian vein remains anterior to the anterior scalene. Hypertrophy, spasm, or fibrous bands at the scalene triangle contribute to neurogenic and arterial thoracic outlet syndrome, and the dorsal scapular nerve commonly pierces the middle scalene on its way to levator scapulae and rhomboids, a pattern relevant when posterior shoulder pain accompanies neck symptoms. For regional anesthesia, clear appreciation of the scalene planes improves interscalene brachial plexus block needle trajectory and helps explain complications such as diaphragmatic paresis when local anesthetic spreads toward the phrenic nerve along the anterior scalene. Use this asset for gross anatomy lectures on the cervical region, for operative anatomy figures in texts discussing thoracic outlet decompression and first-rib resection, or for anesthesia training materials illustrating surface-to-deep relationships during ultrasound-guided interscalene block. It also fits rehabilitation and sports medicine content where scalene overactivity and rib elevation are discussed alongside sternocleidomastoid, trapezius, and deltoid mechanics. Anatomical accuracy verified by SciePro's Medical Advisory Board.