Delayed osteon formation in long-bone diaphysis of an 11-year-old giant cow with dermal dysplasia.
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The transverse sections of radius diaphysis in an 11-year-old giant Holstein cow with dermal dysplasia of a collagen disorder-related skin fragility (Cow 1), probably based on increasing turnover of the dermal collagen as reported previously, were morphologically and physico-chemically investigated. Cow 1 had about one and a half times as much as the body weight of normal Holstein cows, aged 5 to 6.5 years with stabilized growth. The bone samples were compared with those of a 12-year-old Holstein cow as controls (Cow 2). It has been reported that the long-bone diaphysis of young calves and some herbivorous dinosaurs are occupied with laminar bone showing a concentric appositional formation, and that such a laminar bone is characteristically seen during the growing period of some farm animals and large dogs that show very rapid growth rates. Cow 1 had a smaller number of osteons than Cow 2 in the outer-half layer of the diaphysis, and showed an intermediate type between Cow 2 and a 1-year-old Holstein ox in the entire layers, although their bone volumes were similar among them. There were no significant differences in Ca and P concentrations and the Vickers microhardness values between the bone matrix of Cow 1 and Cow 2. The bone-collagen fibrils of Cow 1 showed uneven diameters and a disordered arrangement. Thus, there may be some relation in collagen formation between the bone matrix of Cow 1 and the dermis. From the remaining volume of laminar bone, Cow 1, aged 11 years, had probably shown growth until quite recently, so that we consider that Cow 1 became a giant animal, in the same way as some herbivorous dinosaurs. (+info)
Histomorphological study on pattern of fluid movement in cortical bone in goats.
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Streaming potential is considered one of the most important mechanisms to moderate the function of osteoblasts and osteocytes in bone growth, remodeling and fracture repair. The present study was designed to demonstrate the fluid flow pattern in the cortical bone matrix in an animal model using undecalcified histological techniques. Immediately after injection of ferritin into the tibia nutrient artery of four adult goats, the animals were euthanized. Undecalcified transverse and longitudinal blocks of cortical bone obtained from the tibial diaphysis were immersed in Perl's reagent and embedded in methyl methacrylate. Sections were cut and ground to 30-50 microm thickness for histomorphological evaluation at different magnifications and focusing levels. A serial grinding technique was used to validate the observations made at different focusing levels. As expected, ferritin was observed in the interstitial compartment in both transverse and longitudinal sections. In osteons sectioned transversely, the pattern of centrifugal movement of ferritin marker was demonstrated as single or multiple halos around the Haversian canal. The most apparent halo in osteons with multiple halos was the one found closest to the Haversian canal. The total number of identifiable single or multiple halos increased or was altered when counting was made with higher magnification or at different focusing levels, respectively. Irregular and incomplete ferritin halos indicated structural complexity of the osteons. Overall, the pattern of ferritin movement was consistent with bulk interstitial fluid flow influenced by both hydrostatic pressure and transudation. This study demonstrated for the first time multiple concentric halos of the fluid flow marker ferritin around Haversian canals in the cortical interstitial compartment. The results suggest that the undecalcified technique might be a useful method for qualitative and quantitative studies on cortical fluid flow. (+info)
Characteristics of bone ingrowth and interface mechanics of a new porous tantalum biomaterial.
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We have studied the characteristics of bone ingrowth of a new porous tantalum biomaterial in a simple transcortical canine model using cylindrical implants 5 x 10 mm in size. The material was 75% to 80% porous by volume and had a repeating arrangement of slender interconnecting struts which formed a regular array of dodecahedron-shaped pores. We performed histological studies on two types of material, one with a smaller pore size averaging 430 microm at 4, 16 and 52 weeks and the other with a larger pore size averaging 650 microm at 2, 3, 4, 16 and 52 weeks. Mechanical push-out tests at 4 and 16 weeks were used to assess the shear strength of the bone-implant interface on implants of the smaller pore size. The extent of filling of the pores of the tantalum material with new bone increased from 13% at two weeks to between 42% and 53% at four weeks. By 16 and 52 weeks the average extent of bone ingrowth ranged from 63% to 80%. The tissue response to the small and large pore sizes was similar, with regions of contact between bone and implant increasing with time and with evidence of Haversian remodelling within the pores at later periods. Mechanical tests at four weeks indicated a minimum shear fixation strength of 18.5 MPa, substantially higher than has been obtained with other porous materials with less volumetric porosity. This porous tantalum biomaterial has desirable characteristics for bone ingrowth; further studies are warranted to ascertain its potential for clinical reconstructive orthopaedics. (+info)
Regulatory pathways in blood-forming tissue with particular reference to gap junctional communication.
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Blood formation by pluripotent stem cells and their progeny is thought to be regulated by receptor-ligand interactions between cell-substrate, cell-cell and cell-matrix in the bone marrow. Primitive stem cells form progenitors and, in their turn, these give rise to haemopoietic progeny which are more specifically committed in that they can form progressively fewer types of blood cells. Recently we have established that direct cell-cell communication via gap junctions may be part of this regulatory system. Connexin43 gap junctions metabolically couple the three dimensional meshwork of bone marrow stromal cells to form a functional syncytium in which some blood-forming cells are also coupled. The expression of gap junctions in the bone marrow is markedly upregulated when there is an urgent and substantial demand for blood-formation; for example, following cytotoxic injury after 5-fluorouracil or irradiation; or during neonatal blood-formation and in the epiphysis of growing bones. Chemical blockade of gap junctions blocks blood-formation in long-term cultures but is reversible after the blockade has been relieved. This short review highlights briefly the known regulatory mechanisms of blood-formation with especial attention to gap junctional communication. (+info)
The anisotropic Young's modulus of equine secondary osteones and interstitial bone determined by nanoindentation.
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The equine radius is a useful subject for examining the adaptation of bone histology to loading because in life the anterior cortex is loaded almost entirely in tension, the posterior cortex in compression. The histology of the two cortices is correspondingly different, the osteones and the interstitial lamellae in the posterior cortex having a more transversely oriented fibre arrangement than those in the anterior cortex. Presumably as a result of this histological difference, the posterior cortex is stronger in compression than the anterior cortex; the anterior cortex is stronger in tension than the posterior cortex. We here use nanoindentation to examine how the Young's modulus of elasticity of secondary osteones and interstitial lamellae in the anterior and posterior cortices varied as a function of angle. The anterior osteones were stiffer than the posterior osteones when tested in the direction parallel to the bone's long axis, but became progressively relatively less stiff as the angle increased; at 90 degrees, they were less stiff than the posterior osteones. Although the interstitial lamellae were stiffer than their neighbouring osteones, the same relationship between anterior and posterior interstitial lamellae as a function of angle was found as for the osteones. The anisotropy of these Young's moduli determined by nanoindentation shows a close relationship with what was to be expected from the histological findings. (+info)
Super-osteons (remodeling clusters) in the cortex of the femoral shaft: influence of age and gender.
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Previous studies of cortical remodeling in the fractured femoral neck indicated that the merging of spatially clustered remodeling osteons could result in the formation of deleteriously large cavities associated with femoral neck fracture. This study aimed to identify whether remodeling osteons in the femoral shaft were also clustered and to assess the influence of age and gender. Microradiographic images of femoral mid-shaft cross-sections from 66 subjects over 21 years of age were analyzed to determine the number, size and location of all Haversian canals. Those most recently remodeled were identified using an edge-detection algorithm highlighting the most marked differential gradients in grey levels. Cluster analysis (JMP software) of these osteons identified the proportion of recently remodeled osteons that were within 0.75 mm clusters. As in the femoral neck, remodeling osteons were significantly more clustered than could occur by chance (real, 59.4%; random, 39.4%; P < 0.0001). The density of these clusters (number/mm(2)) was not significantly associated with subject age or gender but was greatest near the periosteum and decreased toward the marrow cavity (periosteal 0.043 +/- 0.004; mid-cortex 0.028 +/- 0.003; endosteal 0.017 +/- 0.002). Cortical porosity increased with age. The presence of giant canals (diameter >385 microm) was inversely related to the presence of clusters (R(2) = 0.237, P < 0.0001). This data suggest that remodeling osteons tend to be spatially colocalized in the shaft as they are in the neck of the femur and their presence is independent of age or gender. We propose that these remodeling clusters be termed super-osteons. The negative relationship between super-osteons and giant canals raises the intriguing possibility that loss of the control of remodeling depth results in the merging of osteonal systems to form deleteriously large cortical cavities with a marked reduction in bone strength. (+info)
Bone adaptation to load: microdamage as a stimulus for bone remodelling.
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Mechanical loading in the proximal radius was increased by ulnar osteotomy (Group O), altered by Steinmann pinning (Group P) or unaltered in sham operated controls (Group C) in skeletally mature female sheep, aged 2-4 years. A series of intravenous fluorochromes were given to label bone formation and fuchsin-stained microdamage assessed at intervals of up to 24 weeks. Microcracks were present in all groups and were found in the original cortex near the periosteal surface. No microcracks were found in the new, fibrolamellar bone laid down at periosteal or endosteal surfaces. Mean microcrack length (49 microm, SD 10 microm) did not differ between groups or overtime. Microcrack numerical and surface densities and resorption cavity density peaked in all groups at 6 weeks, consistent with a regional acceleratory phenomenon (RAP), but the peaks were significantly greater in Group O. The density of refilling or secondary osteons peaked at 10 weeks and the mean time required for the formation of an osteon was 7.51 +/- 0.59 weeks. Fatigue-induced microdamage is normally present in bone and is increased due to repetitive loading of the mechanically overloaded radius. The location and timing of microcracks, resorption cavities and secondary osteons are consistent with the activation-resorption-formation remodelling cycle and suggest that microdamage is a stimulus for bone remodelling. (+info)
Laminar bone as an adaptation to torsional loads in flapping flight.
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Using a new histometric method, the orientation of primary osteons was measured in the main long bones of adult mallards (Anas platyrhynchos). In the light of previous biomechanical and ontogenetic studies, a functional hypothesis is proposed, explaining the histological differences observed between long bones; laminar bone tissue, mainly found in the wing bones, may be a biomechanical adaptation to torsional loads caused by flapping flight. (+info)