Study aim: Vertebral deformity, intervertebral disc disorganisation, and changes to vertebral bone architecture are morphological features associated with degeneration of the spine and with back pain. Vertebral strength is determined by bone size, shape, bone mineral density, microarchitecture, and bone material properties (collagen characteristics, mineralisation, microdamage). Despite its importance to vertebral mechanics, no studies have reported on the variation of bone microdamage present in whole human vertebrae. Thus, the aim of this study was to assess regional changes in trabecular bone microdamage in association with bone microarchitecture and resorption in the human lumbar vertebra.
Methods: L2 vertebrae were obtained from 12 human cadaveric spines (6 males, aged 53-82 years; 6 females, aged 56-87 years). Parasagittal slices cut from each vertebral body were en bloc-stained in basic fuchsin, cut into 9 sectors, and resin embedded. Histomorphometric assessment of trabecular bone microarchitecture, in vivo bone microdamage, and extent of bone resorption was undertaken.
Results: Data analysis for the 9 sectors and the antero-posterior axis revealed few differences. For the cranio-caudal axis, the mid-vertebral region had the lowest bone volume fraction (p<0.03), trabecular number (p<0.02), and highest trabecular separation (p<0.02). Microcrack density parameters were highest in the mid-vertebral region (p<0.04 vs. caudal); with the shortest crack lengths observed in the caudal region (p<0.05 vs. mid). Diffuse microdamage was minimal or absent. Bone resorption was highest in the cranial region (eroded bone surface, p<0.04).
Conclusions: For the cranio-caudal axis of the L2 human vertebra, the mid-vertebral region may be biomechanically compromised due to reduced bone volume and microarchitectural changes being accompanied by an increased microcrack burden. The increased bone resorption found in the cranial region may be an adaptive response to intervertebral disc degeneration. The implications of these observations are being further investigated with comparison to available biomechanical and intervertebral disc grading data.