The middle scalene is the largest scalene and forms the posterior wall of the interscalene triangle. The brachial plexus roots (C5, C6, C7) emerge between the anterior and middle scalenes.
| Origin | Posterior tubercles of transverse processes of C2-C7 |
|---|---|
| Insertion | First rib — posterior to the subclavian artery groove |
| Nerve Supply | Ventral rami of C3-C8 |
| Blood Supply | Ascending cervical artery |
| Actions | Elevates the first rib; Ipsilateral lateral flexion; The largest of the three scalenes |
|---|
The long thoracic nerve (C5, C6, C7) pierces the middle scalene before forming the nerve to serratus anterior. Middle scalene fibrosis from cervical rib or anomalous first rib can compress the lower brachial plexus producing TOS. The brachial plexus block (interscalene block) is deposited between the anterior and middle scalenes.
Palpated posterior to the anterior scalene as the larger lateral neck muscle during deep inspiration.
Middle scalene fibrosis from anomalous rib or fibromuscular band compressing the lower brachial plexus (C8, T1) producing ulnar-distribution TOS symptoms.
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