Scalenes

Scalenus Anterior
Scalenus Posterior
Scalenus Medius

The Scalenes work together to aid in breathing. During inhalation, they lift the first and second rib. They also bend the vertebral column to one side or the other. The Scalenus Posterior is the smallest of the scaleni. It originates from the lower two or three cervical vertebrae and attaches to the second rib. It is innervated by the anterior rami of C7 and C8. The Scalenus Medius is the largest and longest of the scaleni. It originates from the lower six cervical vertebrae and attaches to the first rib. It is innervated by the anterior rami of C3 to C8. The Scalenus Anterior lies deep at the side of the neck, behind the sternocleidomastoid. It originates from the typical cervical vertebrae (C3 to C6) and attaches to the first rib. It is innervated by the anterior rami of C4 to C6.

The roots of the brachial plexus, and subclavian artery lie between the scalenus anterior and scalenus medius muscles (scalene hiatus). The phrenic nerve and subclavian vein lie on the anterior surface of scalenus anterior.

Thoracic outlet syndrome (TOS) refers to compression of the subclavian vessels and nerves of the brachial plexus in the region of the thoracic inlet. These neurovascular structures of the upper extremity may be compressed by a variety of anatomic structures, including, but not limited to the scalene muscles. Symptoms of subclavian artery compression include fatigue, weakness, coldness, ischemic pain, and paresthesia of the upper limb.