Where it is
From the sternum and clavicle to the mastoid process behind the ear.
What it does
One side turns the head to the opposite side; both together flex the neck. It also acts as an accessory muscle of breathing.
Clinical relevance
- Use of the sternocleidomastoid during breathing is a sign of respiratory distress.
- It is a landmark for the internal jugular vein (central lines) and for assessing jugular venous distension.
- Torticollis in infants involves a shortened sternocleidomastoid.
Nursing focus
- Report accessory muscle use, tripod positioning and nasal flaring in a dyspneic client.