Micro-computed tomography study of the subchondral bone of the vertebral endplates in a porcine model: correlations with histomorphometric parameters.

PURPOSE: Subchondral bone (SCB) of the vertebral endplates (VEP) is the principal site of changes in vertebral trabecular microarchitecture secondary to intervertebral disc degeneration. However, the microstructure of this region has not yet been clearly characterized.
METHODS: One thoracic and one lumbar vertebral unit (vertebra-disc-vertebra) was removed in nine pigs aged 4 months. Three samples (one central and two laterals) were taken from each VEP. Micro-CT examination and histomorphometric measurements of the subchondral trabecular bone of the VEP were carried out. Correlations between micro-CT and histological parameters were sought.
RESULTS: Trabecular network was significantly denser [increased bone volume fraction (BV/TV) and trabecular number (Tb.N), decreased intertrabecular separation (Tb.Sp)] in the cranial endplates of the vertebral units. It was also significantly denser and less well organized [increased degree of anisotropy (DA)] in the centre of the VEP. The thickness of the cartilage endplate (CEP), SCB and growth cartilage were significantly lower in the centre of the VEP. There was a significant negative correlation between BV/TV, Tb.N and DA with the thicknesses of the CEP and SCB whereas Tb.Sp was positively correlated with these two parameters.
CONCLUSION: We observed densification of the trabecular network in the centre of the VEP overlying the nucleus pulposus, partly related to thinner hyaline cartilage. Densification is associated with more anisotropic architecture that could cause lower mechanical strength in this area. This study provides new information on the microarchitecture of the SCB of the VEP which will make it possible to validate future models.