Posterior cervical line drawn between the anterior aspects of the C1 and C3 spinous processes

(A) Posterior cervical line of Swischuk. Line is drawn from the cortex of the spinous process of C1 to the cortex of the spinous process of C3. Relationship of the line to cortex of the spinous process of C2 is noted. If the line is situated more than 2.0 mm anterior to the cortex of the spinous process of C2, underlying cervical pathology should be present. This line should be used only with anterior displacement of C2 on C3.
(B) Pseudosubluxation of C2 on C3 with normal posterior cervical line in a 2-year-old child. Note apparent widening of prevertebral soft tissue.
(C) Abnormal posterior cervical line with an underlying hangman's fracture. Actual offset is 4 mm.