PTH treatment would add to this periosteal expansion resulting in a relatively higher periosteal bone formation rate compared to the metaphysis. It is also possible that the increased endocortical metaphyseal bone is the result of “corticalization” of the subcortical trabecular elements. We also saw that while the degree of bone apposition was evenly distributed over the endo- and periosteal surface of
the diaphysis, it varied quite largely over the endo- and periosteal surface of the metaphysis. This could indicate that bone apposition is stimulated more in certain locations than others, which may also partly be the result of remodeling due to linear growth, which still is present in the Foretinib chemical structure adult rat [28, 53]. This study was limited by a treatment period with PTH of 6 weeks. It was found that bone volume fraction in the meta- and epiphyseal trabecular bone and
cortical thickness in the meta- and diaphysis continued to increase linearly. It is very likely though that these increases will wane after a longer treatment period. Although no trabecular tunneling was detected, it would be interesting to determine how trabecular structure would develop further over time as bone mass continues to increase. Another limitation lies in the translation of our rat study to click here clinical practice. It is known that rat cortical bone is not subject to Haversian FK506 ic50 remodeling , which has shown to lead to different responses to PTH compared to species with Haversian remodeling, in which negative [54, 55] and Morin Hydrate no effects [56, 57] on cortical thickness were found. Also, rats in our study were subjected to serial radiation resulting from CT scanning; however, we have previously shown that eight weekly scans do not lead to detectable radiation damage . Since the total number of scans in this study was six and the shortest interval between scans was 2 weeks, we do not expect any radiation damage. Finally, concern has been raised regarding the predictive value of CT-derived
tissue mineralization [58, 59]. It could be that thicker trabeculae would lead to more beam hardening effects, which would result in a lower average mineralization. The fact that we found an increased mineralization degree indicates that this is most likely not due to beam hardening. An explanation for our results could be that when trabeculae thicken after PTH treatment, the center is not being remodeled anymore resulting in an increased mineralization of this bone. The algorithm calculating the mineralization peels off two voxels of the outside of the bone, which is probably the new less mineralized bone. This is thus not incorporated in the calculation, which could result in the increased mineralization.