5 7 1 39 8 5. It is the distance in mm between the basion and the superior extension of the posterior cortical margin of the body of the axis in the median midsagittal plane.
The basion axial interval bai is the horizontal distance between the basion and the posterior cortex of the axis used in the diagnosis of atlanto occipital dissociation injuries.
Basion dens interval radiology. The classification of these injuries is based upon the displacement of the occiput. Our goal was to establish the normal values of a recently described new imaging parameter the basion cartilaginous dens interval in children. Alignment of spine figure 6 3 b anterior spinal line solid red line.
3 4 4 64 not reliable. Harris et al 2 calculated that 95 of adults in their study population had a bdi and bai less than 12 mm and considered this value as the upper limit of normal. Measured on a midline sagittal image the distance between the inferior tip of the basion and the tip of the dens is less than 12 mm in 95 of adults.
The method used by this group included the basion dens interval bdi originally described by wholey et al 4 as well as the basion axial interval bai. In 95 of adults the basion dens interval was less than 12 mm and in 98 the basion was situated no more than 12 mm anterior or 4 mm posterior to the posterior axial line fig 2. Widening of the basion dens interval is an important sign of cranioverterbral junction injury.
The current literature on basion dens interval in children is sparse and based on bony measurements with variable values. The basion axial interval is the distance between the basion and this line. Lateral radiograph figure 6 3 a basion dens interval.
An increase in this distance indicates instability. A few fractures of the ring of the atlas c1 and the dens of the axis c2 may be better visualized on the ap open mouth view figure 6 2 c. It is the distance from the most inferior portion of the basion to the closest point of the superior aspect of the dens in the median midsagittal plane.
An abnormal distance between the dens or posterior axial line and the basion suggests failure or insufficiency of the alar ligaments tectorial membrane or both. The basion dens interval was obtained by measuring the shortest distance from the most inferior portion of the basion to the closest ossified point of the superior aspect of the dens in the midsagittal plane. The distance from the basion to the posterior axial line basion axis interval and the distance from the basion to the tip of the dens basion dens interval should each be less than 12 mm figure 2.
It was measured in the midsagittal plane. Powers ratio a b 0 8 0 08 0 9. The basion dens interval bdi is a parameter used to define the normal articulation between the occiput and the cervical spine.
The basion dens interval bdi is the distance between the basion and the tip of the dens used in the diagnosis of atlanto occipital dissociation injuries.