ESPE Abstracts

Histomorphometric evaluation of transiliac bone samples represents a standardized tool for studying bone metabolism, yielding information on bone both static and dynamic parameters on bone formation and static resorption parameters. Beyond these routine evaluations, the identical bone biopsy sample can be further used to assess submicroscopic tissue characteristics of the bone matrix. At the material level, bone matrix can be considered as a mineral/organic matrix composite where mineral particles consisting of stiff carbonated hydroxyapatite platelets (2–4 nm in thickness) are embedded within long elastic fibrils of type 1 collagen. One important determinant of bone material quality is the bone mineralization density distribution (BMDD) that can be measured in the bone biopsy block, using quantitative Backscattered Electron Imaging (qBEI). BMDD provides information on the mean calcium content within the mineralized bone matrix as well as the heterogeneity of the calcium distribution, reflecting bone turnover, mineralization kinetics and tissue age. The same biopsy block can further be used to characterize properties of the organic matrix by Raman microspectroscopy with a spatial resolution of ~1 μm. In combination with fluorescence labeling, this offers the capability of characterizing properties of the organic matrix in addition to the mineral, both as a function of tissue age. The BMDD and matrix parameters assessed in children and adolescents are remarkably constant and normative data have been established that can now be used as references in pediatric osteology. Such data may be complemented by even higher resolution techniques, such as small-angle X-ray scattering that provide information on mineral particle size. Together with bone histomorphometry, multi-scale characterization of the bone tissue contributes to differential diagnosis in unclear bone fragility, in genetic diseases, including osteogenesis imperfecta, pycnodysostosis or X-linked hypophosphatemia or in metabolic disorders such as chronic kidney disease. These analyses also support the understanding of the underlying pathophysiological mechanisms and the effects of treatment.