Age and decay in the lumbar vertebral body. Are we looking in the right place and for the right tissue?

Abstract

The present study began by examining variations in the degree of mineralisation of 'bone' in lumbar vertebral bodies. Thick para-sagittal slices of L2 (38 male, 31 female, 70±15 years); embedded PMMA; plane block surfaces carbon coated; quantitative 20kV BSE SEM; then polished and stained with iodine vapour to reveal (uncoated, at 50Pa) uncalcified matrix. Stitching allowed high resolution imaging of entire vertical sections. High-contrast x-ray microtomography (XMT, n = 15) was conducted at 30 micron voxel resolution. Thin ground sections were cut from block faces by dual photon laser ablation and examined by polarised light microscopy and again after staining. Half of all 'bone' lies in bin 5 of 8 of our qBSE calcified tissue distribution, corresponding to a 1.99g/ml density gradient centrifugation peak. 28% is highly mineralised (bins 6-8). Much of this is not bone. Typical failure modes, central compression and implosion of erstwhile disc content into the central cancellous domain, involve calcified cartilage/fibrocartilage of the end-plate. Anterior wedge compression fractures and collapse fractures also include the cortex. This frequently contains Sharpey fibre bone, calcified fibrous periosteum, calcified ligament and may be very thin anteriorly. These five non-bone calcified matrices should be factored into thinking about mechanical properties.