Microscopy Focus: I13-2

Glucocorticoids are a class of anti-inflammatory drugs that are often prescribed for conditions such as asthma, rheumatoid arthritis and autoimmune diseases. However, long-term treatment can occasionally lead to a form of secondary osteoporosis known as glucocorticoid induced osteoporosis (GIOP). This can result in a rapid increase in bone fracture risk, which is believed to arise from the degradation in bone matrix quality.

X-ray Micro-computed Tomography (microCT) was used on I13- 2 to determine the specific alterations in bone quality, and observe the mechanistic consequences of these changes in GIOP.

MicroCT allowed the vascular canal network of the tibiae from osteoporotic mice to be visualised. The effective voxel size was 1.6 μm3, providing a spatial resolution of 3.2 μm and field of view of 4.2 x 3.5 mm. Tomographic scans were obtained using photon energy of 18 keV and exposure time was 0.1s.

In combination with in situ mechanical testing with small angle X-ray diffraction and quantitative backscattered electron imaging, the techniques allowed the measurement of the deformation of mineralised collagen fibrils and nano-mechanical parameters such as effective fibril modulus and the fibril strain ratio. A significant reduction in the quantity of fibril modulus was found in the diseased mice compared with wild-type mice, and microCT showed that the intracortical architecture was disrupted. Together, this information revealed how bone quality changes could increase fragility in GIOP.

Tibiae mid diaphysis. microCT transverse images (top) and 3D reconstructions (bottom) showing cavities (red), inner cortico-endosteal tissue (purple), and lacunae network (yellow). © The authors. Adapted from Karunaratne et al. under CC-BY 4.0; http://creativecommons.org/licenses/by/4.0/.