"type I: the atlas is rotated on the odontoid with no anterior displacement (most common)"
"type II: the atlas is rotated on one lateral articular process with 3 to 5 mm of anterior displacement, indicating transverse ligament injury"
"type III: comprises rotation of the atlas on both lateral articular processes with anterior displacement greater than 5 mm, indicating transverse and alar ligament injury"
"type IV: rotation and posterior displacement of the atlas"
"Atlantoaxial rotatory fixation is a disorder of C1-C2 causing impairment in neck rotation. The anterior facet of C1 is fixed on the facet of C2. It may be associated with dislocation of the lateral mass of C1 on C2."
Expected headings
"Mechanism"
"There are several ways in which a fixation can occur:"
"In a non-traumatic setting, flexion and extension views may be performed. The expected distance between the anterior arch of C1 and the dens in the fully flexed position should be"
"On CT, C1 and the head are rotated out of alignment around a vertical axis. If this is a fixed defect, C2 is rotated in conjunction with C1."