Sternothyroid muscle

The sternothyroid muscle is an infrahyoid muscle of the neck. It acts to depress the hyoid bone.

Structure

The two muscles are in contact with each other proximally, but diverge distally.

Origin

The sternothyroid arises from the posterior surface of the manubrium of the sternum from the midline to the notch for the first rib, and the posterior margin of the first costal cartilage.

Insertion

It inserts onto the oblique line of the lamina of thyroid cartilage.

Innervation

The sternothyroid muscle receives motor innervation from branches of the ansa cervicalis.

Relations

The sternothyroid muscle is shorter and wider than the sternohyoid muscle and is situated deep to and partially medial to it.

Variations

The muscle may be absent or doubled. It may issue accessory slips to the thyrohyoid muscle, inferior pharyngeal constrictor muscle, or the carotid sheath.

Actions/movements

The sternothyroid muscle indirectly depresses the hyoid bone by means of pulling the thyroid. When the hyoid bone is fixed, it instead elevates the larynx.

Clinical significance

The upward extension of a thyroid swelling is prevented by the attachment of the sternothyroid to the thyroid cartilage. A goitre can therefore only grow to the front, back or middle but no higher.