Recent work has demonstrated the highly variable and unpredictable external dimensions of the dens (odontoid process). No date have been available regarding internal dimensions. Quantitative computed tomography analysis of 120 axis vertebrae allowed nondestructive measurement of external and intarnal dens dimensions. The external computed tomography measurements correlated well with caliper-derived data. Minimum internal dens dimensions and cortical thicknesses in the sagittal and transverse planes are reported. Some axis vertebrae may not be amenable to internal fixation of type II dens fractures. Preoperative planning should include quantitative computed tomography analysis of the dens.
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