The Orientation of Nanoscale Apatite Platelets in Relation to Osteoblastic-Osteocyte Lacunae on Trabecular Bone Surface

The orientation of nanoscale mineral platelets was quantitatively evaluated in relation to the shape of lacunae associated with partially embedded osteocytes (osteoblastic-osteocytes) on the surface of deproteinised trabecular bone of adult sheep. By scanning electron microscopy and image analysis, the mean orientation of mineral platelets at the osteoblastic-osteocyte lacuna (Ot.Lc) floor was found to be 19A degrees A A +/- A 14A degrees in the tibia and 20A degrees A A +/- A 14A degrees in the femur. Further, the mineral platelets showed a high degree of directional coherency: 37 +/- A 7 % in the tibia and 38 +/- A 9 % in the femur. The majority of Ot.Lc in the tibia (69.37 %) and the femur (74.77 %) exhibited a mean orientation of mineral platelets between 0A degrees and 25A degrees, with the largest fraction within a 15A degrees-20A degrees range, 17.12 and 19.8 % in the tibia and femur, respectively. Energy dispersive X-ray spectroscopy and Raman spectroscopy were used to characterise the features observed on the anorganic bone surface. The Ca/P (atomic %) ratio was 1.69 +/- A 0.1 within the Ot.Lc and 1.68 +/- A 0.1 externally. Raman spectra of NaOCl-treated bone showed peaks associated with carbonated apatite: nu(1), nu(2) and nu(4) PO4 (3-), and nu(1) CO3 (2-), while the collagen amide bands were greatly reduced in intensity compared to untreated bone. The apatite-to-collagen ratio increased considerably after deproteinisation; however, the mineral crystallinity and the carbonate-to-phosphate ratios were unaffected. The similar to 19A degrees aEuro20A degrees orientation of mineral platelets in at the Ot.Lc floor may be attributable to a gradual rotation of osteoblasts in successive layers relative to the underlying surface, giving rise to the twisted plywood-like pattern of lamellar bone.