Annika vom Scheidt

Annika vom Scheidt

The heterogeneity of cortical thickness in thoracic vertebrae differs between premenopausal and postmenopausal women and compensates trabecular bone loss

Aims

Vertebral fractures, a common debilitating condition for postmenopausal women, is often ascribed to a loss of trabecular bone. Trabecular bone quality in vertebrae is heterogeneous and age-dependent. Unfortunately, heterogeneity and age-dependence are understudied for the cortical shell of the vertebra, even though it supports up to 40% of the vertebral load [1,2] and gains relevance with aging [3]. Thus, we aimed to compare vertebrae from pre- and postmenopausal women and assess the cortical shell thickness in subregions.

Methods

We performed microCT (13μm) and HRpQCT scans (41μm) on thoracic vertebrae (T12) from premenopausal (n=9, 32±6y) and postmenopausal (n=13, 71±5y) women. The thickness of the cortical shell was evaluated with a validated custom-written algorithm in 9 subregions of left vertebral bodies. Vertebrae from the postmenopausal group were divided into subgroups based on severity of osteophyte occurrence. Osteophyte characterization was based on Zukowski et al. [4].

Results

In the premenopausal group, cortical thickness was higher in mid-horizontal subregions compared to adjacent superior or inferior regions (p<0.0025). The post-menopausal group showed a more homogeneous distribution. Postmenopausal women without osteophytes had a thinner cortical shell than premenopausal women in six of nine regions (p<0.05). Osteophyte occurrence resulted in higher cortical thickness in the anterior superior region (p<0.001).

Conclusion

In premenopausal women, the cortical shell is thicker in regions where trabecular volume is typically lower [5]. Further cortical bone in these regions is preserved in postmenopausal women, indicating a loading-related compensatory function. In postmenopausal women, the loss of cortical thickness appeared to be partially reversed by osteophyte growth, helping to explain why osteophytes are inversely related to fracture risk [6]. This study underlines the need to include more complex representations of the cortical shell in whole vertebra finite element models and further investigate the influence of cortical vertebral bone loss on vertebral fracture risk in postmenopausal women.

[1] Rockoff et al. Calcif Tissue Res. 1969;3(2):163-75
[2] Eswaran et al. J Bone Miner Res. 2006 Feb;21(2):307-14.
[3] Andresen et al. Br J Radiol. 1998 Jul;71(847):759-65.
[4] Zukowski et al. J Anat. 2012 Jan; 220(1): 57-66.
[5] Hulme et al. Bone. 2007 Dec;41(6):946-57.
[6] Roux et al. Ann Rheum Dis. 2008 Feb;67(2):224-8.