The sternocleidomastoid muscle runs from the mastoid process to the sternoclavicular joint. The tendonous insertion of the muscle becomes prominent when the patient turns his head to the side opposite the muscle to be examined.


The sternocleidomastoid muscle is often stretched in hyperextension injuries causing tenderness to palpation.

Torticollis is a condition in which the head is abnormally turned or tilted to one side. This may be due to localized swellings in one of the sternocleidomastoid muscles.

The trapezius and sternocleidomastoid are both innervated by the spinal accessory nerve (cranial nerve IX). This is a result of the fact that these two muscles originate as one embryologically. The also share a common origin at the mastoid process.