Atlantooccipital junction: standards for measurement in normal children.

This study describes a simple method for measuring the distance between the occiput and atlas when a distraction-dislocation injury is suspected in a child. Measurements were made at five evenly spaced locations along the atlantooccipital joint on cross-table lateral skull radiographs in 100 normal children. These data were compared with similar measurements in eight patients with proved atlantooccipital dislocation. The mean normal measurement fell between 1.96-2.63 mm for all five points. For boys or girls aged 1-15 years, the normal distance should not exceed 5 mm at any point in the joint. The likelihood that any normal child will have a measurement greater than or equal to 4.5 mm at any point is between 0.4-5.85% (expected false-positive rate).