Sternomastoid paradox.

In the standard routine for testing cranial nerve function following a cerebrovascular accident (CVA) compromising the corticonuclear supply to the cranial nerves, sternomastoid muscle (SCM) function is checked by means of head rotation against resistance. SCM appears to be an exception to the generally contralateral motor weakness resulting from a CVA. The thrust of this article is that appearances can be deceptive: SCM is more likely to be a postural stabilizer than a prime mover in head rotation.