Light micrographs of non-decalcified toluidine blue-stained ground sections of femur defects after 28d of healing.

The defects were created in non-ovariectomised (A-F) or ovariectomised (G-L) rats. The defects were filled with either hydroxyapatite (HA) (A-C and G-I) or strontium calcium phosphate (SCP) (D-F and J-L). The survey images for each group (A = non-OVX HA, D = non-OVX SCP, G = OVX HA, J = OVX SCP) show the pattern of new bone formation (NB) and the distribution of the remaining granules within the defect boundaries. An evident amount of separated granules with various sizes and shapes appears within the HA defects (A and G) and, at least at this magnification, new bone (NB) and bone marrow areas (BM) are more visible in the SCP defects (D and J). The demarcation line between the old bone (OB) and the newly formed bone (NB) at the defect borders is sometimes hardly defined (A and G), but it is well defined in some defects (D). (B, E, H and K) show that the granules are surrounded and interconnected by mature bone (MB) in the central region of the four different defects. A considerable amount of mature bone has formed in the central region of HA defects (B and H), in contrast to the central region of SCP defects (E and K). Multinucleated giant cells (some indicated by black arrows) were detected at the granule surface (H and K). (C, F, I and L) show that the granules are also surrounded and interconnected by mature bone in the peripheral region of the four different groups. The peripheral region of the HA defects are largely occupied by the remaining granules with less mature bone (C and I) and a more mature bone area in the peripheral region of SCP defects (F and L).