middle scalene

The Scalenus medius, also known as the middle scalene, is the largest and longest of the three scalene muscles in the human neck.

Because it elevates the upper ribs, the middle scalene muscle is also one of the accessory muscles of respiration.

And we remove the anterior scalene muscle, the middle scalene muscle and the first rib.

The middle scalene arises from the posterior tubercles of the transverse processes of the lower six cervical vertebræ.

Once the nerve leaves C5 it commonly pierces the middle scalene muscle, and continues deep to levator scapulae and the rhomboids.

Since the nerves of the brachial plexus pass through the space between the anterior and middle scalene muscles, that area is sometimes targeted with the administration of regional anesthesia by physicians.

The brachial plexus emerges between the anterior and middle scalene muscles, superior to the first rib, and passes obliquely and inferiorly, underneath the clavicle, into the shoulder and then the arm.

Thus, the subclavian vein lies anterior to the anterior scalene while the subclavian artery lies posterior to the anterior scalene (and anterior to the middle scalene).

The passing of the brachial plexus and the subclavian artery through the space of the anterior and middle scalene muscles constitute the scalene hiatus (the term "scalene fissure" is also used).

The interscalene block is performed by injecting local anesthetic to the nerves of the brachial plexus as it passes through the groove between the anterior and middle scalene muscles, at the level of the cricoid cartilage.

Thoracic outlet syndrome (TOS) is a syndrome involving compression at the superior thoracic outlet wherein excess pressure placed on a neurovascular bundle passing between the anterior scalene and middle scalene muscles.

The action of the anterior and middle scalene muscles is to elevate the first rib and laterally flex (bend) the neck to the same side; the action of the posterior scalene is to elevate the second rib and tilt the neck to the same side.

From its origin, the subclavian artery travels laterally, passing between anterior and middle scalene muscles, with the anterior scalene (scalenus anterior) on its anterior side and the middle scalene (scalenus medius) on its posterior.