Morphometric analysis of the canal system of cortical bone: an experimental study in the rabbit femur carried out with standard histology and micro-CT

The osteonal pattern of cortical bone is gradually built around
the intracortical vessels by the progression of the cutting cones
(secondary remodelling); therefore, the central canal size can
be used as index of the remodelling activity. An experimental
model in the rabbit femur was used to investigate, through
central canal morphometry and frequency distribution analysis,
the remodelling activity, comparing the middle of the
diaphysis (mid-shaft) with the extremity (distal-shaft) and at
the same level sectors and layers of the cortex in transversal
sections. The study documented a higher density of canals in
the mid-shaft than in the distal-shaft and a higher remodelling
in the distal-shaft. There were no significant differences between
dorsal, ventral, medial and lateral sectors at both midshaft
and distal-shaft levels, while the number of canals was
higher in the sub-periosteal layers than in the sub-endosteal. A
lower threshold of 40 lm2 was observed in the central canal
area. Sealed osteons in the midshaft were 22.43% of the total
number of osteons of the central canal area between 40 and
200 lm2 and 0.44% of those of the distal-shaft. Micro-CT
allowed a 3D reconstruction of the vascular canal system,
which confirmed the branched network pattern rather than the
trim architecture of the traditional representation. Some aspects
like the lower threshold of the central canal size and the
sealed osteons documented the plasticity of the system and its
capacity for adaptation to changes in the haemodynamic
conditions.