Long-term peroral administration of bitter apricot seeds influences cortical bone microstructure of rabbits

Apricot seeds due to the presence of cyanogenic glycoside amygdalin belong to the popular “alternative cancer cures", although anticancer effect of amygdalin remains controversial. This in vivo study points to the effect of long-term peroral administration of bitter apricot seeds on bone microstructure of rabbits since chronic amygdalin toxicity in relation to bone parameters has not been investigated yet. Rabbits (n = 16) were randomly divided into four experimental groups of 4 animals each. Three experimental groups S1, S2 and S3 received commercial feed for rabbits mixed with crushed bitter apricot seeds at doses 60, 300 and 420 mg/kg bw during five months, respectively. The control (C) group received no apricot seeds. The long-term consumption of apricot seeds had no impact on total body weight, femoral weight and femoral length of rabbits. Also, microcomputed tomography (3D analysis) of cortical and trabecular bone tissues did not reveal any significant impact of amygdalin toxicity on relative bone volume, BMD, cortical bone thickness, bone surface, trabecular number, thickness, and their separation. On the other hand, histological (2D) analysis demonstrated evident changes in cortical bone microstructure consistent with a decreased density of secondary osteons in the middle part of substantia compacta due to a replacement of Haversian bone tissue by plexiform bone tissue, vasoconstriction in the primary osteons' vascular canals, Haversian canals, and decreased sizes of secondary osteons in rabbits from S1, S2 and S3 groups. These negative changes are associated with different vascularization and biomechanical properties of cortical bones.     

Preliminary study of histological comparison on the growth patterns of long-bone cortex in young calf, pig, and sheep

Some young large farm animals show a laminar bone formation in the long-bone cortex. Such a laminar bone is gradually replaced by Haversian bone with osteons during their growth periods. In this preliminary study, we observed the transverse ground samples of tibia cortex in young calves, pigs, and sheep by backscattered electron imaging. The cortex bones of all the newborn (NB) animals were basically formed with laminar bone structures. The NB and 1-month-old (1-M) calves had a typical concentric structure of laminar bone, whereas the NB and 1-M pigs showed a wire-netting bone with laminar-bone units. The NB sheep was similar to the calf rather than the pig. In the growth rate of bone volume, sheep was similar to calf up to 6 months after birth (6-M). Such calf and sheep showed a more rapid ratio of bone volume than pig. A few osteons had initially appeared in the innermost layer of the 6-M calf. A 1-year-old (1-Y) calf showed scattered osteons in the bone cortex, but many laminar-bone units were still retained in the outer layer. A 6-M pig had many osteons in the entire cortex but only a few osteons in the outermost layer. In the 6-M sheep, no osteons were observed, whereas a 1-Y sheep showed a relatively small number of osteons mainly in the middle layer but a higher osteon-volume than the 1-Y calf. In the 1-Y sheep, the more widely absorbed areas by bone-remodeling with osteons were observed as compared with the 1-Y calf, and the bone volume was decreased from the 6-M into the 1-Y sheep because of the remarkable bone-absorption. Thus, calf kept on possessing many laminar-bone units for a longer time in the growth period than sheep, while pig showed the earliest bone-remodeling with osteons. These results may be caused by their different body size and withers height in calf and sheep after growing and the difference of the dependence upon mother's body during juvenile period between pig and calf with sheep. The initial region of osteon formation may be distinguishable among their animals, respectively. However, further detailed investigations of their young animals at successive stages will be necessary.     

Comparative bone histology of adult horses (Equus caballus) and cows (Bos taurus)

Bone microstructure of domestic herbivores is still not completely understood. Indeed, works focused on the bone histology of numerous Mammalian species frequently led to misunderstandings because of the high number of variations such as the kind of bone, section orientation, species, breed and age. Moreover, attempts to identify the species in archaeozoological studies by a mere qualitative approach have not been encouraging and in recent years quantitative methods, based on image processing and statistical analysis, have appeared. The present study was undertaken to determine whether morphometrical and morphological differences exist in the compact bone structure of the femur and humerus between horses and cows. Measurements such as area, perimeter, minimum and maximum diameter of osteons and Haversian canals as well as the osteonal density were carried out on cross sections of eight humeri and eight femurs of the two herbivores investigated. In agreement with other authors, the qualitative investigation confirmed that the compact bone of horses and cows can be classified as dense Haversian tissue. Osteons of the horse were more numerous and composed of a higher number of well-defined lamellae when compared with the cow. Diameter, perimeter and area of osteons and Haversian canals were always higher in horses than in cows and this pattern could be related to the different locomotor behaviour of these animals.     

Differences in femoral compact bone tissue microscopic structure between adult cows (Bos taurus) and pigs (Sus scrofa domestica)

The purpose of this investigation was to study in detail compact bone tissue microscopic structure of adult cows and pigs with an emphasis to find an adequate key for the species identification. Altogether 18 femurs were analysed. Each of the bones was sectioned at the smallest breadth of their diaphysis. Specimens were prepared using standard histological equipment, producing thin sections approximately 80-100 mum thick. The qualitative differences between investigated species were examined in anterior, posterior, medial and lateral views of thin sections. The quantitative ones were counted using the specific computer software Scion Image. We measured the area, perimeter, minimal and maximal diameter of the Haversian canals, the Haversian systems and the vascular canals of primary osteons. After that a discriminant function analysis was used for the species identification. According to our results the basic structural pattern of femur diaphysis was primary vascular plexiform in both species. However, non-vascular bone tissue was identified in cows and resorption lacunae were found between the secondary osteons in pigs. The measured variables of the Haversian canals, the Haversian systems and the primary osteon's vascular canals were higher in most cases in cows. Classification functions for investigated species give a correct classification of 64.69% of cases. This percentage value can be increased by integrating conclusions from the qualitative analysis.     

Changes in compact bone microstructure of rats subchronically exposed to cadmium

Background

Chronic exposure to cadmium (Cd), even at low concentrations, has an adverse impact on the skeletal system. Histologically, primary and secondary osteons as basic structural elements of compact bone can also be affected by several toxicants leading to changes in bone vascularization and mechanical properties of the bone. The current study was designed to investigate the effect of subchronic peroral exposure to Cd on femoral bone structure including histomorphometry of the osteons in adult male rats.In our study, 20 one-month-old male Wistar rats were randomly divided into two experimental groups. In the first group, young males received a drinking water containing 30 mg of CdCl₂/L, for 90 days. Ten one-month-old males without Cd intoxication served as a control group. After 90 days of daily peroral exposure, body weight, femoral weight, femoral length, cortical bone thickness and histological structure of the femora were analysed.

Results

We found that subchronic peroral application of Cd had no significant effect on body weight, femoral length and cortical bone thickness in adult rats. On the other hand, femoral weight was significantly increased (P < 0.05) in Cd-intoxicated rats. These rats also displayed different microstructure in the middle part of the compact bone where vascular canals expanded into central area of substantia compacta and supplied primary and secondary osteons. Additionally, a few resorption lacunae which are connected with an early stage of osteoporosis were identified in these individuals. Histomorphometrical evaluations showed that all variables (area, perimeter, maximum and minimum diameter) of the primary osteons’ vascular canals, Haversian canals and secondary osteons were significantly decreased (P < 0.05) in the Cd group rats. This fact points to alterations in bone vascularization.

Conclusions

Subchronic peroral exposure to Cd significantly influences femoral weight and histological structure of compact bone in adult male rats. It induces an early stage of osteoporosis and causes reduced bone vascularization. Histomorphometrical changes of primary and secondary osteons allow for the conclusion that the bone mechanical properties could be weakened in the Cd group rats. The current study significantly expands the knowledge on damaging action of Cd on the bone.     

Structural changes in femoral bone tissue of rats after subchronic peroral exposure to selenium

Background

The role of selenium (Se) on bone microarchitecture is still poorly understood. The present study aims to investigate the macroscopic and microscopic structures of femoral bone tissue in adult male rats after subchronic peroral administration of Se.

Methods

Twenty one-month-old male Wistar rats were randomly divided into two experimental groups. In the first group (Se group) young males were exposed to 5 mg Na₂SeO₃/L in drinking water, for 90 days. Ten one-month-old males without Se administration served as a control group. At the end of the experiment, macroscopic and microscopic structures of the femurs were analysed using analytical scales, sliding instrument, and polarized light microscopy.

Results

The body weight, femoral length and cortical bone thickness were significantly decreased in Se group rats. These rats also displayed different microstructure in the middle part of the femur, both in medial and lateral views, where vascular canals expanded into the central area of the bone while, in control rats, these canals occurred only near the endosteal surfaces. Additionally, a smaller number of primary and secondary osteons was identified in Se group rats. Histomorphometric analyses revealed significant increases for area, perimeter, maximum and minimum diameters of primary osteons’ vascular canals but significant reductions for all measured variables of Haversian canals and secondary osteons.

Conclusions

Se negatively affected the macroscopic and microscopic structures of femoral bone tissue in adult male rats. The results contribute to the knowledge on damaging impact of Se on bone.     

Effects of a single intraperitoneal administration of cadmium on femoral bone structure in male rats

Background

Exposure to cadmium (Cd) is considered a risk factor for various bone diseases in humans and experimental animals. This study investigated the acute effects of Cd on femoral bone structure of adult male rats after a single intraperitoneal administration.

Methods

Ten 4-month-old male Wistar rats were injected intraperitoneally with a single dose of 2 mg CdCl₂/kg body weight and killed 36 h after the Cd had been injected. Ten 4-month-old males served as a control group. Differences in body weight, femoral weight, femoral length and histological structure of the femur were evaluated between the two groups of rats. The unpaired Student''s t-test was used for establishment of statistical significance.

Results

A single intraperitoneal administration of Cd had no significant effect on the body weight, femoral weight or femoral length. On the other hand, histological changes were significant. Rats exposed to Cd had significantly higher values of area, perimeter, maximum and minimum diameters of the primary osteons'' vascular canals and Haversian canals. In contrast, a significant decrease in all variables of the secondary osteons was observed in these rats.

Conclusions

The results indicate that, as expected, a single intraperitoneal administration of 2 mg CdCl₂/kg body weight had no impact on macroscopic structure of rat''s femora; however, it affected the size of vascular canals of primary osteons, Haversian canals, and secondary osteons.     

Sex-related variation in compact bone microstructure of the femoral diaphysis in juvenile rabbits

Background

While gross morphological changes in the skeleton between males and females are well know, differences between sexes in the histomorphology are less known. It is important to have knowledge on the bone structure of rabbits, as this is a widely used species in biomedical research. A study was performed to evaluate the association between sex and the compact bone morphology of the femoral diaphysis in juvenile rabbits.

Methods

Seventeen clinically healthy 2–3 month-old rabbits (9 females, 8 males) were included in the study. The rabbits were euthanized and the right femur was sampled for analysis. 70–80 microns thick bone sections of the femoral diaphysis were prepared using standard histological equipment. The qualitative histological characteristics were determined according to internationally accepted classification systems while the quantitative parameters were assessed using the software Scion Image. Areas, perimeters, minimum and maximum diameters of primary osteons'' vascular canals, Haversian canals and secondary osteons were measured. Additionally, blood plasma concentrations of progesterone, corticosterone, IGF-I, testosterone and estradiol were analyzed.

Results

Qualitative histological characteristics were similar for both sexes. However, variations of certain quantitative histological characteristics were identified. Measured parameters of the primary osteons'' vascular canals were higher in males than for females. On the other hand, females had significant higher values of secondary osteons parameters. Differences in Haversian canals parameters were only significant for minimum diameter.

Conclusion

The study demonstrated that quantitative histological characteristics of compact bone tissue of the femoral diaphysis in juvenile rabbits were sex dependent. The variations may be associated with different growth and modeling of the femur through influence by sex-specific steroids, mechanical loads, genetic factors and a multitude of other sources. The results can be applied in experimental studies focusing on comparison of the skeletal biology of the sexes.     

Study of osteogenesis in adult sheep on a high and a low calcium ration by means of fluorescing bone markers

The rate of osteogenesis was studied in 8 non-pregnant, non-lactating Friesian dairy sheep, 3–6 years old, by means of a treatment with 3 different bone seeking agents. Four sheep were fed a low calcium ration (LCa : 1.8 g Ca/d) and four other sheep a high calcium ration (HCa : 12.7 g Ca/d). The bone markers, oxytetracycline-HCl, alizarine-complexon and demeclocycline-HCl, were administred at intervals of 6 weeks, and the sheep were killed 1 week after administration of the last marker. In undecalcified cross sections from the middle of ribs 2, 10 and 12, and from the proximal and distal parts of rib 10, the numbers of labelled osteons and the number of osteons with 1, 2 or 3 markers were counted under fluorescent microscopy.In the ribs of sheep from the LCa group, the number of labelled osteons and the quantity of labels per osteon tended to be higher than those of sheep from the HCa group. When osteogenic activity was compared in the different sites of ribs analysed, lowest osteogenic activity was observed in the proximal part of the 10th rib.The use of fluorescing markers offers the possibility of studying osteogenic activity over a certain period of time in adult sheep.     

Simultaneous subchronic exposure to selenium and diazinon as possible risk factor for osteoporosis in adult male rats

Background

Osteoporosis and its main health outcome, fragility fractures, are large and escalating health problems. Skeletal damage may be the critical result of low-level prolonged exposure to several xenobiotics in the general population, but the mechanisms of their adverse effects are not clearly understood. The current study was aimed to investigate the possible ability of simultaneous subchronic peroral administration of selenium (Se) and diazinon (DZN) to induce changes in bone of adult male rats.In our study, twenty 1-month-old male Wistar rats were randomly divided into two experimental groups. In the first group, young males were exposed to 5 mg Na₂SeO₃/L and 40 mg of DZN/L in drinking water, for 90 days. Ten 1-month-old males without Se and DZN intoxication served as a control group. At the end of the experiment, macroscopic and microscopic structures of the femurs were analysed using analytical scales, sliding instrument, and polarized light microscopy.

Results

The body weight, femoral length and cortical bone thickness were significantly decreased in rats simultaneously exposed to Se and DZN (P < 0.05). These rats also displayed different microstructure in the middle part of the compact bone where vascular canals expanded into central area of substantia compacta. The canals occurred only near endosteal surfaces in rats from the control group. Additionally, a smaller number of primary and secondary osteons, as well as a few resorption lacunae were observed near endosteal surfaces in rats simultaneously administered to Se and DZN. The resorption lacunae as typical structures of bone resorption manifestation are connected with an early stage of osteoporosis. Histomorphometric analysis revealed that area, perimeter, maximum and minimum diameters of primary osteons’ vascular canals were significantly increased (P < 0.05) in the Se-DZN-exposed rats. On the other hand, all measured variables of Haversian canals and secondary osteons were considerable reduced (P < 0.05) in these rats.

Conclusions

Simultaneous subchronic peroral exposure to Se and DZN induces changes in macroscopic and microscopic structures of the femurs in adult male rats, and also it can be considered as possible risk factor for osteoporosis. The current study contributes to the knowledge on damaging impact of several xenobiotics on the bone.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 6. Bone parameters in the third metacarpal and third metatarsal bones

AIM: To determine the effect of a known training regimen on the size and mineral content of the third metacarpal (Mc3) and third metatarsal (Mt3) bones of 2-year-old Thoroughbred horses trained on racetracks. METHODS: Mc3 and Mt3 of seven horses trained on grass and sand tracks were scanned at several sites using conventional quantitative and peripheral computed tomography (CT). Bone dimensions and density in the diaphysis and epiphysis were compared with those from seven untrained horses. Calcein label was injected in two clusters, during Weeks 9 and 12. The extent and rate of diaphyseal modelling was determined by confocal fluorescent microscopic examination of thin plane parallel sections of the mid-metacarpal region. RESULTS: Volumetric bone mineral density (BMDv) of the epiphysis was markedly higher and of the diaphysis was slightly higher in trained compared with untrained horses, but greater bone size in the trained horses had the greatest effect on an index of bone strength. Active osteons, defined as Haversian systems containing calcein label, were fewer, of smaller diameter at the time of calcein injection, and had a greater bone apposition rate in trained than in untrained horses. CONCLUSIONS: Conventional training of 2-year-old Thoroughbred racehorses over a 13-week period had a significant effect on bone size, density and strength index when compared to untrained horses. CLINICAL RELEVANCE: Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 6. Bone parameters in the third metacarpal and third metatarsal bones

AIM: To determine the effect of a known training regimen on the size and mineral content of the third metacarpal (Mc3) and third metatarsal (Mt3) bones of 2-year-old Thoroughbred horses trained on racetracks.

METHODS: Mc3 and Mt3 of seven horses trained on grass and sand tracks were scanned at several sites using conventional quantitative and peripheral computed tomography (CT). Bone dimensions and density in the diaphysis and epiphysis were compared with those from seven untrained horses. Calcein label was injected in two clusters, during Weeks 9 and 12. The extent and rate of diaphyseal modelling was determined by confocal fl uorescent microscopic examination of thin plane parallel sections of the mid-metacarpal region.

RESULTS: Volumetric bone mineral density (BMDv) of the epiphysis was markedly higher and of the diaphysis was slightly higher in trained compared with untrained horses, but greater bone size in the trained horses had the greatest effect on an index of bone strength. Active osteons, defined as Haversian systems containing calcein label, were fewer, of smaller diameter at the time of calcein injection, and had a greater bone apposition rate in trained than in untrained horses.

CONCLUSIONS: Conventional training of 2-year-old Thoroughbred racehorses over a 13-week period had a significant effect on bone size, density and strength index when compared to untrained horses.

CLINICAL RELEVANCE: Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.     

The Canalicular System and the Osteoblast Domain in Human Secondary Osteons

The lacunar–canalicular system in human secondary osteons was examined by two complementary techniques: light microscopy analysis of undecalcified thick sections and the SEM cortex‐fractured surface technique. Unlike the earlier definitions of ‘osteoblastic domain’ presented as the matrix volume produced by osteoblasts in the process of osteon infilling, this study measured the domain by the length of osteoblast dendritic processes. The domain extension was defined along radial vectors advancing from the reversal line towards the central canal. According to their lengths, domains were divided into three classes: peripheral, intermediate and internal. The mean length of peripheral domains was significantly shorter than those of the intermediate and internal domains. This suggests that the infilling process is modulated by an initial preparatory phase characterised by osteoblast adhesion to the wall of the cutting cone, and a limited matrix synthesis, followed by a regular matrix volume apposition organised in concentric layers. In addition to the radial canaliculae arranged along converging vectors in planes perpendicular to the central canal, we distinguished a further class of canaliculae, the equatorial canaliculae originating from the major perimeter of the lacuna and spreading out radially in the plane of the same lacuna (therefore, perpendicularly to the radial canaliculae). The whole lacunar–canalicular network was structured as a closed system around the vascular axis of the central canal with very few canaliculae crossing the reversal line and connecting the neighbouring osteons. These anatomical observations contribute to our knowledge of lacunar–canalicular system development.     

Influence of intensity and changes of physical activity on bone mineral density of immature equine subchondral bone

Reasons for performing study: Subchondral bone provides structural support to overlying articular cartilage and plays an important biomechanical role in osteochondral diseases. Mechanical features of bone correlate strongly with bone mineral density, which is directed by the loading conditions to which the tissue is subjected. Objective: To investigate the influence of physical activity levels on subchondral bone mineral density (sBMD) in foals during early development. Methods: Three groups of foals were subjected to different physical activity levels from birth until age 5 months. A proportion of these foals were subjected to euthanasia at 5 months while remaining foals were subjected to similar physical activity levels for 6 months until euthanasia at 11 months. Osteochondral specimens were collected for measurement of sBMD with peripheral quantitative computed tomography at 2 differently loaded anatomical sites of the proximal phalangeal bone at 1, 2, 3, 4 and 5 mm depth from the osteochondral junction. Results: Growth significantly increased sBMD but by a different amount depending on anatomical location and physical activity level. Significantly higher sBMD was found at the habitually loaded central area in comparison to the intermittently peak loaded marginal site. Exercise increased sBMD throughout the whole depth of analysed tissue, but changes were generally more obvious at a depth of 2 mm. Interestingly, foals subjected to additional sprint training preserved the exercise‐induced sBMD increase at the habitually loaded central area during the 6 months of the second phase of the study. Conclusions: Habitual low‐intensity loading elicits a greater response in sBMD in quantitative terms than high‐intensity low‐frequency loading at the sites investigated in this study. Future sBMD may be influenced by means of well‐tailored exercise regimens at young age. Potential relevance: Specific physical activity levels during early development may potentially reduce the prevalence of osteochondral injury later in life.     

Histological comparison of long-bone cortex between 11-year-old giant cow with dermal dysplasia and the child cow aged 8.5 years

Young calves are known to be formed with laminar bone in long-bone cortex during growing periods and the osteon formation begins later. Previously, we reported that an 11-year-old giant Holstein cow with dermal dysplasia showed a delayed osteon formation. An 8.5-year-old cow, born from the giant Holstein cow, also showed some dermal dysplasia and the outer-half layer of the child almost retained laminar bone similar to that of the mother, although the body weight was approximately normal. The mother had formed the inner circumferential lamella and the child was going to form the inner circumferential lamella, but their outer circumferential lamellas were not formed yet in both of them, when compared with a 12-years-old cow as a control of the mother. Therefore, we suggest on long-bone formation pattern that the child resembled the mother rather than the control, and that the child had more or less succeeded to the mother genes of delayed osteon formation as well as dermal dysplasia which seemed to be genetic collagen disorder, although there were mild gene appearances.     

Fluorosis as a probable cause of chronic lameness in free ranging eastern grey kangaroos (Macropus giganteus).

A population of eastern grey kangaroos (Macropus giganteus) inhabiting heathland and farmland surrounding an aluminum smelter at Portland, Victoria, Australia, exhibited clinical signs of lameness. An investigation was undertaken to determine the cause of this lameness. Hematology, necropsy, histopathology, fecal egg count, total worm count, reproductive status, and the population age range were examined and failed to reveal any additional underlying disease state. The specific problem of lameness was addressed with bone histopathology, radiography, quantitative ultrasonography, microradiography, and multielement analysis of bone ash samples. The significant lesions observed were: osteophytosis of the distal tibia and fibula, tarsal bones, metatarsus IV, and proximal coccygeal vertebrae; osteopenia of the femur, tibia, and metatarsus IV; incisor enamel hypoplasia; stained, uneven, and abnormal teeth wear; abnormal bone matrix mineralization and mottling; increased bone density; and elevated bone fluoride levels. Microradiography of affected kangaroos exhibited "black osteons," which are a known manifestation of fluorosis. Collectively, these lesions were consistent with a diagnosis of fluorosis.     

Gender,caponization and exogenous estrogen effects on lipids,bone and blood characteristics in Taiwan country chickens

This study investigated gender, caponization and exogenous estrogen effects on lipids, bone and blood characteristics in Taiwan country chickens. Thirty male chickens were caponized at 8 weeks (capons); 15 capons were injected with estrogen (5 mg/bird estradiol 3‐benzoate) every 2 weeks from 8 to 28 weeks, and 15 sham‐operated male (shams) chickens and 15 females were selected for this trial. The results showed that the shams had lower relative abdominal and chest subcutaneous fat than females (P < 0.05). The estrogen‐treated capons had greater relative abdominal and chest subcutaneous fat than shams and capons (P < 0.05), which might result from higher blood very low‐density lipoproteins and triacylglycerol concentrations (P < 0.05). Caponization could dramatically increase relative abdominal fat (506%; P < 0.05). The shams had higher tibia weight and biomechanical properties, such as maximum bone strength and bending moment values than the capons (P < 0.05). Tibia biomechanical properties were reduced by estrogen treatment (P < 0.05). The females obtained the lowest biomechanical value in all treatments (P < 0.05). Histological examination revealed cavity formation in the cortical bone of estrogen‐treated capons and female chickens, which suggested that estrogen reduced bone biomechanical properties by destroying its structural integrity.     

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 mid-shaft 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 μm² 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 μm² 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.     

Site-specific adaptive remodeling of Greyhound metacarpal cortical bone subjected to asymmetrical cyclic loading

OBJECTIVE: To quantify geometric, inertial, and histomorphometric properties at the mid-diaphyseal level of left and right metacarpal bones (MCB) of racing Greyhounds. SAMPLE POPULATION: MCB from 7 racing Greyhounds euthanatized for reasons unrelated to MCB abnormalities. PROCEDURES: Mid-diaphyseal transverse sections of left and right MCB were stained with H&E or microradiographed. Images of stained sections were digitized, and cross-sectional area, cortical area, and maximum and minimum area moments of inertia of each bone were determined. Histomorphometric data (osteonal density, osteonal birefringence, and endosteal new lamellar bone thickness) were collected in 4 quadrants (dorsal, palmar, lateral, medial). Values were compared between limbs and among bones and quadrants. RESULTS: Cross-sectional area, cortical area, and maximum and minimum moments of inertia of left MCB-IV and -V were significantly greater, compared with contralateral bones. Overall osteonal densities in the dorsal quadrants of left MCB were greater, compared with lateral and medial quadrants. Also, percentage of birefringent osteons was significantly greater in the dorsal quadrant of left MCB-III, -IV, and -V, compared with the palmar quadrant. Thickness of new endosteal lamellar bone was not significantly influenced by limb, bone, or quadrant. CONCLUSIONS AND CLINICAL RELEVANCE: Increased cortical thickness and geometric properties of left MCB-IV and -V of Greyhounds, together with altered turnover and orientation of osteons in the dorsal quadrants of left MCB, are site-specific adaptive responses associated with asymmetric cyclic loading as a result of racing on circular tracks. Site-specific adaptive remodeling may be important in the etiopathogenesis of fatigue fractures in racing Greyhounds.