| dc.description.abstract | A new paradigm for bone formation in remarkable endosteal bone appositional rates in rat distal femu. A Boyde, T Zikmund. Dental Physical Sciences, QMUL, London, UK. Poster LB14 presented at Bone Research Society/British Society for Matrix Biology Joint Meeting, 01-03 Sept 2015, Edinburgh. Objectives: to study details of bone growth rates and mechanisms in the distal femur of young rat using multiple combined 3D imaging methods. Methods: fluorescent mineralisation front labels - calcein was given at 12 days and tetracycline 3 days before termination. X-ray microtomography (microCT 8μm voxels) of right femurs was conducted before cutting the femurs longitudinally in the midline. The lateral halves were PMMA embedded for block face microscopy, using confocal LM for histology and to read labels. 20kV BSE SEM was used to image mineral content: more BSE imaging after iodine staining was also used for histology. Finally, all bone was dissolved to produce 3D casts of marrow and capillary blood vessel canal space. The medial halves were macerated for 3D BSE SEM. After analysis of the right-side data, we studied left femurs with 6 μm microCT, then cut them transversely to create thick 'rings' at defined distances from the distal condyles. The end faces were polished and used for imaging labels with confocal LM and the samples were then macerated for 3D SEM. All these types of image were cross correlated to produce composites which can be best understood by dynamic, sequential, repetitive display techniques. Results and Conclusions: remarkably high values for endosteal apposition were measured, with nearly matching high periosteal resorption rates to be assumed. In places, almost the entire 400μm thickness of the shaft was translocated in 15 days. This rapid endosteal bone growth is associated with the inclusion of capillary blood vessels which penetrate the osteoblastic layer at near normal incidence to the formative surface at ~50 micron spacing. This is a previously undescribed mode of compact cortical lamellar bone formation.Trabeculae drift centrally in parallel with cortical surfaces. Thus their double label intervals must be understood in a full 3D context. MicroCT imaging ‘loses’ small trabeculae which are physically retained even in macerated SEM samples. Real loss of trabeculae occurs by their burial in compact bone at endosteal growth surfaces as well as through resorption. The ‘gold standard’ must be held to be the combination several imaging methods. | en_US |
