Cortical bone mineral status evaluated by pQCT, quantitative backscattered electron imaging and polarized light microscopy

摘要

Synergy can be achieved using multiple imaging modalities to reveal cortical bone adaptation at organ, tissue and ultrastructural levels. Peripheral quantitative computed tomography (pQCT) measurement showed significant regional variations of cortical bone mineral density (cBMD) in the distal tibia and distal radius, independent of menopausal status. The higher cBMD was related to its prevalent compressive stress. Circularly polarized light (CPL) microscopy supported this by showing a preferred transverse to oblique collagen fibre orientation. Quantitative backscattered electron (QBSE) imaging study of osteon morphometry and degree of mineralisation in the cadaveric tibia and radius showed that the variation of cBMD was due to differences in percentage of intracortical porosity (IP), rather than to the variation of mineralisation. The distal tibia had significantly lower cBMD than the distal radius. This lower cBMD was compensated by having greater cortical thickness, polar moment of inertia, and collagen fibre orientation index. The tibia, being subject to habitual dynamic compressive loading as compared with the non-weight-bearing nature of the radius, may activate a higher remodelling rate, which does not allow full secondary mineralisation. This was evidenced in the study showed lower cBMD and greater percentage of IP; thus, the compensatory increase in bone geometry is meant to withstand the sustained bend and torsion loading in this region. This chapter demonstrates that compressive loading is more osteogenic bringing about greater regional BMD. The design of exercise intervention programs to enhance bone quality should consider the strain mode effect. Compensation between the material density and structure is evidenced which allows bone strengthening. Regional bone adaptation, as revealed by multiple imaging modalities, allows better understanding of changes at different levels of bone organization.