Dr Michael Doube has been awarded a BBSRC grant for the following study: "Is the plate to rod transition in trabecular bone loss a real phenomenon or a spurious of a misused metric?"
Dr Doube explains that a latticework of bony trabeculae stiffens the internal spaces of many bones. Trabecular bone loss is a normal physiological response to reduced mechanical load, occurring during bed rest, in sedentary lifestyles, and during the weightlessness of spaceflight. Bone loss is also a normal, undesirable, part of ageing which occurs particularly rapidly in women after menopause. Reduced bone mass is strongly associated with increased fracture risk. In addition to bone mass, bone architecture is thought to play a crucial role in trabecular bone's force transmission and fracture resistance.
Bone architecture is defined by standard measurements such as trabecular thickness and rod-plate geometry, among others. When trabecular bone fails, each trabecula might fail by buckling, shear or crumpling. Bone biologists believe that plate-like trabeculae resist higher loads than rod-like trabeculae and that plate-like trabeculae convert to rod-like trabeculae during bone loss, creating a 'double-whammy': reduced bulk resistance to load due to decreased bone mass and reduced resistance to trabecular element failure due to rod-like geometry. Whether a plate-to-rod transition actually occurs in bone loss is in doubt, because rods and plates have been measured with an algorithm called structure model index (SMI).
Unfortunately, there is a high, artefactual, correlation between SMI and bone mass, meaning that the plate-to-rod transition may not be a real result. Over 900 papers have cited SMI, many linking bone loss and plate-rod transition. This project aims to overturn the dogma there is a plate to rod transition in bone loss using 3D X-ray microtomography (XMT) image data sets archived from previous experiments. To measure rods and plates independent of bone mass, we will optimise and validate a new method, ellipsoid factor (EF), that defines rods and plates by the shape of the biggest ellipsoid that fits within each bony region. Rods can fit long, javelin-shaped ellipsoids, while plates can fit flat, discus-shaped ellipsoids. Having identified rods and plates in bone samples, we will correlate rods and plates with mechanical behaviour using finite elements analysis in the physiological load range for bulk behaviour and overload range for trabecular element failure behaviour. The primary benefit of the work is improved understanding of true geometric and mechanical changes in bone loss, along with the new EF method incorporated into free and commercial software.