The posterior scalene is the smallest and most posterior of the three scalene muscles, running from the lower cervical transverse processes to the outer surface of the second rib. It elevates the second rib during forced inspiration as an accessory breathing muscle and assists in lateral cervical flexion. Unlike the anterior and middle scalenes whose compression of the brachial plexus causes thoracic outlet syndrome, the posterior scalene is rarely involved in nerve compression.
| Origin | Posterior tubercles of the transverse processes of C4 through C6 |
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| Insertion | Outer surface of the second rib, posterior to the serratus anterior attachment |
| Nerve Supply | Ventral rami of the lower cervical spinal nerves (C6, C7, C8) |
| Blood Supply | Ascending cervical artery |
| Actions | Elevation of the second rib during forced inspiration; Ipsilateral lateral flexion of the neck; Flexion and slight rotation of the neck |
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It elevates the second rib during forced inspiration in activities requiring maximal respiratory effort and provides lateral cervical stabilisation during ipsilateral neck loading.
The posterior scalene is involved in breathing pattern dysfunction alongside the anterior and middle scalenes when the diaphragm is underused and upper chest breathing predominates. Its trigger points refer pain into the lateral arm and hand in a pattern that can be confused with radiculopathy. Scalene releases for thoracic outlet syndrome typically focus on the anterior scalene, with the posterior scalene rarely requiring surgical attention.
The posterior scalene is palpable in the posterior triangle of the neck posterior to the middle scalene, running from the lower cervical transverse processes toward the second rib, accessible between the trapezius and sternocleidomastoid.
Acute tear from a sudden lateral flexion or whiplash mechanism producing posterolateral neck pain, rarely requiring specific treatment beyond general neck rehabilitation.
