The scalenus posterior is the smallest and deepest of the three scalene muscles, running from the lower cervical transverse processes to the second rib behind the middle scalene. It is an accessory muscle of forced inspiration that stabilises and elevates the second rib. It is rarely individually implicated in pathology but is part of the scalene complex involved in thoracic outlet syndrome.
| Origin | Posterior tubercles of the transverse processes of C4 through C6 |
|---|---|
| Insertion | External surface of the second rib |
| Nerve Supply | Ventral rami of C6, C7, C8 |
| Blood Supply | Ascending cervical artery |
| Actions | Elevates the second rib during forced inspiration; Ipsilateral lateral flexion of the lower cervical spine |
|---|
The posterior scalene's insertion on the second rib anchors it against the pull of the intercostal muscles during forced inspiration, stabilising the second rib as an anchor point for the intercostal expansion above.
The scalenus posterior is identified and released during comprehensive scalenectomy for thoracic outlet syndrome. Its deep position makes it easily overlooked during anterior approaches to the lower cervical spine.
Not individually palpable due to its deep position beneath the anterior and middle scalenes.
Posterior scalene involvement in scalene muscle spasm contributing to thoracic outlet and cervicogenic headache syndromes.
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