Aims: The shape and the structure of cortical bone of the diaphysis is the result of the continual resorption/ replacement process where the two phases have well regulated temporal sequence and spatial localization. Different methods can be employed to measure the appositional growth but their possible application to structural studies has not been so far considered.

The broad interest of this study was addressed to the mechanisms which control the structural modelling of cortical bone in the course of the long growth and development, therefore a morphometric evaluation appeared the more suitable method for the possibility to examine large segments of the bone.

Methods: The study was carried out on the femurs of four male New Zealand white rabbits. The left femurs were prepared with the techniques for undecalcified bone and studied in incedent fluorescent light. The right femurs were decalcified, prepared in sections and studied in bright field, in polarized light and in phase contrast.

Ditigital microscope images were analyzed utilizing the software Cell D: the cortical area was measured and the number of vascular canals was counted and expressed as a function of the cortical area (n/mm²). The total cortical area, the density of vascular canals and the frequency distribution for area classes in the cortex of mid-shaft and distal-shaft was compared with paired student t test and Pearson chi-square test respectively.

Results and Conclusions: The canals distribution for area classes showed a significant prevalence for actually structuring osteons in the distal shaft: these data demonstrate the higher rate of bone remodelling of the most recent apposed bone at the extremities of the shaft. On the contrary there were not significant differences among sectors at levels of the mid-shaft and distal-shaft.