Anatomy of the intracortical canal system. Scanning electron microscopy study in rabbit femur.

The current model of compact bone is that of a
system of longitudinal (Haversian) canals connected by
transverse (Volkmann’s) canals. Models based on histology
or microcomputed tomography lack the morphologic detail
and sense of temporal development provided by direct
observation. Using direct scanning electron microscopy
observation, we studied the bone surface and structure of
the intracortical canal system in paired fractured surfaces in
rabbit femurs, examining density of canal openings on
periosteal and endosteal surfaces, internal network nodes
and canal sizes, and collagen lining of the inner canal
system. The blood supply of the diaphyseal compact bone
entered the cortex through the canal openings on the
endosteal and periosteal surfaces, with different morphologic
features in the midshaft and distal shaft; their density
was higher on endosteal than on periosteal surfaces in the
midshaft but with no major differences among subregions.
The circumference measurements along Haversian canals
documented a steady reduction behind the head of the
cutting cone but rather random variations as the distance
from the head increased. These observations suggested
discontinuous development and variable lamellar apposition
rate of osteons in different segments of their trajectory.
The frequent branching and types of network nodes suggested
substantial osteonal plasticity and supported the
model of a network organization. The collagen fibers of the
canal wall were organized in intertwined, longitudinally
oriented bundles with 0.1- to 0.5-lm holes connecting the
canal lumen with the osteocyte canalicular system.