Acquired torticollis with atlantoaxial rotary subluxation

(A) The head of this child is in the typical position of rotatory atlanto-axial subluxation: tilted to the left, with the chin rotated to the right. Unlike in patients who have congenital muscular torticollis, the right sternocleidomastoid muscle is tight, suggesting an attempt to straighten the neck.
(B, C) Dynamic computed-tomography scans of the upper cervical spine in a patient who had rotatory atlanto-axial subluxation. (B) The head is rotated approximately 45 degrees to one side, with the contralateral lateral mass of the first cervical vertebra moving forward on the cephalad articulating facet of the second cervical vertebra. (C) The head cannot be rotated past the midline, and the relationship of the first and second cervical vertebrae is unchanged.