Design, morphometry and development of the secondary osteonal system in the femoral shaft of the rabbit

Abstract

The architecture of the diaphyseal bone is closely correlated with the cortical vessel network, whose pattern develops in the course of growth. Various methods have been applied to clarify the three-dimensional anatomy of the cortical canal system, but there is still disagreement about the geometry, blood supply, flux dynamics and factors controlling canal geometry during bone growth and remodeling. A modification of the currently employed dye-injection method was applied to study the vessel network of the whole hemi-shaft of the rabbit femur in mature bones (8-month-old rabbits) and growing bones (1.5-month-old rabbits). The cortical vascular tree of the hemi-shaft of the femur was injected with black China ink and observed in full-thickness specimens of the cortex. The same specimens were then processed for histology. A comparative study of the middle diaphysis (mid-shaft) with the distal extremity (distal shaft) was performed in both young and old rabbit femurs. The longitudinally oriented pattern of the vessel network was seen to develop in the diaphysis of mature femurs, while at the extremity of the shaft of the same specimen the network showed a reticular organization without a dominant polarization. The vessels were significantly higher in the mid-shaft than in the distal shaft of the old femurs ( P < 0.0001), as was their diameter ( P < 0.05). In the group of young rabbits at mid-shaft level the longitudinally oriented pattern of the vessel network was not yet completely developed, without their being significant differences in length and diameter between the mid-shaft and distal shaft. The differentiation of the mid-shaft from the distal shaft was confirmed histologically by the presence, in the latter, of longitudinal calcified cartilage septa between osteons. This pattern of structural organization and development of the intracortical vascular network has not been previously reported. The cells primarily involved in polarization of the remodeling process were the osteoclasts at the top of the cutting cones advancing from the proximal and distal metaphyses toward the midshaft. This suggests, first, a relationship with the longitudinally oriented structures already present in the cortex near the metaphysis (the calcified cartilage septa) and then with the columns of interosteonic breccia, which were formed as a secondary effect of the longitudinal polarization of the remodeling process. Our observations did not enable us to substantiate the model of two different systems, one of longitudinal vessels (Havers) and the other of connecting transversal vessels (Volkmann), but suggested instead that there is a network whose loops lengthen in the direction of the major bone axis in the course of growth and secondary modeling. The associated morphology supported the view that the type of structural organization of the tubular bone cortex is primarily determined by an inherited constitutional factor rather than by mechanical strains.

Assessment of bone vascularization and its role in bone remodeling

“…This technique is still used for the analysis of cortical vessels in animal models. 55 Later on, vascular corrosion casts were obtained after infusion and polymerization of methylmethacrylate resin followed by bone matrix digestion and scanning electron microscopy imaging. Beside resin, rubber such as latex can be infused; however, its molecular size and viscosity limit its penetration into the fine branches of the vascular network and only the primary arteries and a few of the larger secondary arterioles may be injected, 56 restricting its use to anatomy studies.…”

Scanning electron microscopy study of bone intracortical vessels using an injection and fractured surfaces technique

“…The left femurs were decalcified in Osteosoft (Merck Sharp & Dome, Rome, Italy) at 37°C for 2 months, and the mid-part of the diaphysis (about 10 mm long) was cut with a blade in a plane perpendicular to the major axis of the bone and the proximal and distal parts were discarded. The central cylinder of each femur was further sectioned: some specimens were observed unstained as full-thickness cortex (Pazzaglia et al 2007), others were embedded in paraffin and transverse or longitudinal sections were stained with haematoxylin-eosine for standard histological observation.…”

A comparison of the microarchitecture of lower limb long bones between some animal models and humans: a review

“…Table 3 presents data about the density of vascular canal openings, vascular canal density and diameter in rabbits with respect to age, gender and anatomical location. The same age and gender specimens have vascular canal densities much greater in the femoral middle shaft than in the distal shaft cortex (Pazzaglia et al 2007). The density of Haversian canals is also greater in the femoral middle shaft (Table 1).…”

“…Osteon development in cortical bone occurs simultaneously with the progression of the vascular network so that the structure of the vascular network almost fits the intracortical canal system (Lee et al 1965;Harris et al 1968;Pazzaglia et al 2007). In humans, as in other mammalian species, osteon structure and geometry depend on the age, sex, height and weight of individuals, genetic differences, differences in lifestyle, and the direction of mechanical loads during locomotion (Britz et al 2009).…”