The Sternocleidomastoid Muscle

Courtesy: Prof Nabile Ebraheim, University of Toledo, Ohio, USA

 

STERNOCLEIDOMASTOID MUSCLE

ANATOMY

• The sternocleidomastoid muscle (also known as sternomastoid) is one of the largest and most superficial cervical muscles located in the superficial layers on the side of the neck.

ORIGIN

• The sternocleidomastoid muscle arises from the medial portion of the clavicle and the manubrium sternii

INSERTION

• It is inserted into the lateral surface of the mastoid process of the temporal bone and lateral half of the superior nuchal line of the occipital bone.

INNERVATION

• The spinal accessory nerve provides motor innervation to the sternocleidomastoid muscle and the trapezius muscle

FUNCTION

• The function of the sternocleidomastoid is to tilt the head to same side and rotate head to the opposite side.
• Both parts of the muscle together tilt the head down.
•  The sternocleidomastoid muscle divides the neck into an anterior triangle and a posterior triangle.

CLINICAL SITUATION

• Contracture of the Sternocleidomastoid muscle in infants – Congenital Muscular Torticollis.
• Congenital Muscular Torticollis is a “packaging deformity” typically caused by contracture of the SCM.
• The infant holds his or her head tilted to one side and has difficulty turning the head due to a tight and shortened sternocleidomastoid muscle.
• Sternocleidomastoid plays a role in displacement of clavicle fractures