Expansion
Same Side Tilt, Opposite Side Turn
Mnemonic
“One turns, both nod”:
- Unilateral contraction - tilts the head to the same side and rotates the face to the opposite side
- Bilateral contraction - flexes the neck, and extends the head at the atlanto-occipital joint
Because it rotates the face away, a right sternocleidomastoid weakness means the patient cannot turn the face to the left, which is how it is tested.
Nerve supply is the accessory nerve (XI) for motor, with C2 and C3 for proprioception, the same nerve as trapezius, so both are tested together.
It is the key surgical landmark of the neck, dividing the anterior from the posterior triangle, and it is an accessory muscle of respiration, which is why it is visible and working in severe respiratory distress.
Congenital torticollis is fibrosis of the muscle, giving a head tilted towards and a face turned away from the affected side.
Expansion
- Same side - lateral flexion, ear toward shoulder
- Opposite side - rotation, chin turns away