Quantitative morphology of the vertebral body cortex

Abstract

The vertebral bodies consist of two main structures, trabecular and cortical bone. The histological changes within the spine, especially in cortical bone, leading to osteoporotic fractures remain, however, poorly understood. Therefore, the complete front column of the spine was removed in 26 autopsy cases without skeletal diseases and in 11 cases with proven osteoporosis. A sagittal segment prepared through the center of all vertebral bodies was undecalcified embedded in plastic, ground to a 1-mm-thick block and stained using a modification of the von Kossa method. The analysis included measurement of the mean cortical thickness of both ventral and dorsal shell (from C3 to L5). The qualitative investigation of the structure of the cortical ring completed the analysis. The skeletally intact specimens had high cortical thickness values in the cervical spine (285 +/- 22 microns), a decrease in the thoracic spine (244 +/- 14 microns) and an increase in the lumbar spine (290 +/- 15 microns). The mean thickness of the ventral shell is in general higher than the thickness of the dorsal shell. The cortical thickness of the spine showed no gender-specific differences (P = n.s.). There was a slight decrease in the cortical thickness with age; however, this decrease and the correlation of cortical thickness to age was only significant below vertebral body T8 (r = 0.225 to 0.574; Pr < 0.05 to Pr < 0.005). Most interestingly, osteoporosis is characterized by a significant decrease in cortical thickness throughout the whole spine. This decrease in cortical thickness was more marked in the dorsal shell (P < 0.05) than in the ventral shell (ventral from C3 to T6 (P < 0.05) below T6 (P = n.s.). We therefore conclude that in osteoporosis, biomechanical competence is affected by both trabecular bone loss and decrease of cortical thickness. This suggests that, in addition to trabecular bone measurements, the cortical thickness is of special interest for diagnostic radiological examinations (CT) to yield clues about the risk of vertebral fractures.