Assessment of Trabecular Bones Microarchitectures and Crystal Structure of Hydroxyapatite in Bone Osteoporosis with Application of the Rietveld Method

The term crystal structure is understood as a set of atoms periodically distributed in space, forming a lattice. The composite material, bone, contains an organic part consisted of collagen and an inorganic part consisted predominantly of hydroxyapatite crystals, having the molecular formula Ca10(PO4)6(OH)2 in its unit cell. The crystal structure of hydroxyapatite can indicate the trabecular bone quality, by the identification of crystallite size, microhardness, microstrain and ratio of calcium and phosphorus in bones of three types: normal, osteopenic or osteoporotic. Osteoporosis is defined by the National Institute of Health as a skeletal disorder characterized by compromised bone strength and increased risk of fracture. Dried trabecular bones of vertebrae L1 columns of nine human cadavers from the São Paulo City Morgue were used. Before sample collection, they were pre-divided into three groups: normal, osteopenic or osteoporotic, through quantitative ultrasound of the calcaneus. The characterization of the three types of bones was made by electron microscopy scanning, microanalysis by energy dispersive spectrometry, microhardness and powder X-ray diffraction with application of the Rietveld method. The results showed a decrease of the crystallite size, hardness, ratio of calcium and phosphorus, trabecular number and bone density and an increase in microstrain values suggesting greater fragility and disruption in the crystalline structure of hydroxyapatite in osteopenic and osteoporotic bone. Microstructural characterization of hydroxyapatite crystals in dry trabecular bone could differentiate the three types of bones (normal, osteopenic and osteoporotic) and supplement assessment of osteoporosis, with an emphasis on bone quality.