Regional variation of cortical shell thickness in human vertebrae in relation to age and osteophyte occurrence

Introduction Vertebral fractures are the result of a loss of vertebral bone mass, which is mostly described as trabecular bone loss. Although most analyses disregard the relevance of the cortical shell, the cortical shell carries around 40 % of the maximum vertebral load [1] [2]] and bears a greater portion of the load with aging [3]. Previous studies showed trabecular bone quality to be heterogeneous and age-dependent; yet, the heterogeneity and age-dependency of the cortical shell remain understudied. Consequently, we aimed to measure cortical shell thickness in subregions and determine whether aging and osteophytes influence the shell thickness.

Methods We included 23 vertebrae (T12) from young (n = 10, 31 ± 6y) and aged (n = 13, 71 ± 5y) women. The vertebrae were scanned with HRpQCT (voxel size 41µm), and the resulting data was reconstructed and segmented by using a fixed threshold. Custom-written algorithms were used to identify the cortical shell and determine its thickness for 9 subregions of left vertebral bodies. Osteophytes were categorized according to Zukowski et al. [4]. Depending on the sum of the osteophyte categories of the individual subregions, vertebrae from the aged group were separated into subgroups: vertebrae with small osteophytes for sum < 6, vertebrae with larger osteophytes for sum ≥ 6.

Results Cortical thickness was higher in mid-horizontal subregions, compared to adjacent superior or inferior regions in the young group (p < 0.05). The pooled aged groups did not show these differences. Vertebrae from aged women with small osteophytes showed a lower cortical shell thickness compared to vertebrae from young in five regions. Vertebrae from aged women with larger osteophytes presented higher cortical thickness in comparison to vertebrae from aged women with small osteophytes, but this was only significant in one region (anterior-superior, p = 0.022).

Discussion The specific regions, where a thicker cortex was found in young women, have previously been linked to a low trabecular volume [5]. This may indicate a compensatory relationship between cortical and trabecular bone in vertebrae. Reduced cortical thickness in aged women reversed with osteophyte occurrence, compared to young appeared to be partially. Together with previous studies reporting osteophyte occurrence to be inversely related to fracture risk [6], our results support further investigation of the relevance of cortical vertebral bone loss for vertebral fracture risk and an inclusion of cortical shells in whole vertebra finite element models.

Keywords vertebral fractures, cortical shell, osteoporosis, aging, regional heterogeneity

Korrespondenzadresse Annika vom Scheidt, Universitätsklinikum Hamburg-Eppendorf, Lottestr. 55A, 22529 Hamburg, Deutschland, Germany

E-Mail [e-mail]

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