Posterior Scalene Muscle, Lateral View

Description

Running from the posterior tubercles of the transverse processes of the mid to lower cervical vertebrae to the external surface of the second rib, the posterior scalene (scalenus posterior) appears as a slender, deep strap along the posterolateral neck. From a lateral perspective it lies posterior to the scalenus medius and lateral to the cervical vertebral column, with its fibers coursing inferolaterally toward the upper thoracic cage. Expect the adjacent posterior triangle landmarks nearby, including the levator scapulae deep and posterior, and the overlying investing fascia and sternocleidomastoid forming the superficial anterior boundary of the region. Small muscle. Deep plane. This angle matters because the posterior scalene sits in the same corridor as structures implicated in thoracic outlet and supraclavicular procedures, even though it is less prominent than the anterior and middle scalenes in routine teaching. The brachial plexus and subclavian artery traverse the interscalene interval between anterior and middle scalene, but lateral dissection that strays posteriorly can encounter scalenus posterior near the suprapleural membrane (Sibson fascia) and the second rib, a relationship relevant during first and second rib exposures and in scalenectomy variants for neurogenic thoracic outlet syndrome. It also helps clarify why trigger points or hypertrophy in the deep scalene group can refer pain toward the shoulder girdle and upper chest wall. Anatomy faculty can drop this into neck dissections, regional anesthesia modules (interscalene block surface anatomy and deep muscular planes), and surgical atlases covering supraclavicular approaches to the thoracic inlet. Authors preparing radiology or cross-sectional anatomy resources will also find it useful for orienting lateral neck muscle layers when correlating to CT and MRI at the C5 to C7 level. Anatomical accuracy verified by SciePro's Medical Advisory Board.