Structural properties of the axis studied in cadaveric specimens.

Peripheral quantitative computed tomography scans of the axis in 20 fresh cadaveric specimens obtained at autopsy were studied to investigate the internal structural properties of the axis. In all specimens, serial scans were done in three planes. The area of the dens consisted of dense cortical and trabecular bone (Region 1, above the base of the dens) and showed statistically significantly greater peripheral quantitative computed tomography values when compared with the anterior part of the body of the axis (Region 2, below the base of the dens). An age-related progressive decrease of peripheral quantitative computed tomography values was observed, with specimens from subjects younger than 40 years showing statistically significantly greater peripheral quantitative computed tomography values when compared with those from subjects older than 40 years. A small area of trabecular bone with decreased density was found close to the anteroinferior edge of the body of the axis in the specimens from younger subjects. In contrast, a large area of trabecular bone with decreased density extending anteroinferiorly to superoposteriorly to the base of the dens was found in the specimens from older subjects. Based on these findings, we think that dens fracture classification systems and fixation techniques should be reconsidered.