Bone density, breaking force and leg muscle mass as functions of weight in bipedal rats

Femur density, femur breaking force and muscle weight on the hind limbs of normal and bipedal rats have been measured. The bipeds had more muscle on the hindlimbs than controls. Increasing muscle mass was associated with increasing femur density and breaking force. It is concluded that weight bearing influences bone density and breaking force through muscle mass.     

Terrestrial locomotion in pterosaurs

On the basis of a well‐preserved pelvis of Anhanguera sp. from the Lower Cretaceous (Aptian) of the Chapada do Araripe, Brazil, the problem of terrestrial locomotion in pterosaurs is discussed. A three‐dimensional reconstruction of the pelvis led to a lateral, dorsal and posterior orientation of the acetabula. By use of the preserved proximal ends of the femora of the same individual, the articulation in the hip socket could be tested. The normal articulation of the femur resulted in a horizontal position of the femur shaft, probably during flight. For constructional reasons the femur could not be brought down to a vertical position. Therefore, a parasagittal swing of the femora necessary for a bird‐like stance and gait must have been impossible. It is suggested that in pterosaurs the wing membrane was attached to the upper leg, which helped in stretching, steering and cambering.

Moreover, on the basis of comparisons of the fossil preservation of pterosaurs Compsognathus and Archaeopteryx in the Solnhofen limestone, it is concluded that the femora of pterosaurs were splayed out laterally, and that they had a semi‐erect gait. They were not bipedal animals, but had to use their fore limbs as well on the ground. Nevertheless, as vertebrates extremely adapted to flight, they could not have been able quadrupeds, either.     

Disuse-induced deterioration of bone strength is not stopped after free remobilization in young adult rats

The effect of unilateral hindlimb immobilization and subsequent free remobilization on mechanical properties of femur was examined in young adult rats. Right hindlimb of 17 weeks old male rats was immobilized for 2 weeks. Rats were sacrificed either directly after immobilization (E0) or after 4 weeks of free remobilization (E4). Mechanical properties in three-point bending as well as dry mass (m_dry), geometry, apparent density (d_app), and mineralization of dry bone tissue were measured post mortem in right and left femora of experimental rats (E0, E4) and in right femora of age-matched controls (C0, C4). Differences between right femora of experimental and control animals and between right and left femora of experimental animals were analyzed. After immobilization only d_app in E0 was significantly lower than in C0. Side-to-side differences in E0 were present only in m_dry and d_app. Surprisingly, 4 weeks after remobilization the differences between experimental and control femora were more pronounced. Mineralization, d_app, maximum bending moment (M_max), yield bending moment (M_y) and stiffness of the right femur were lower in E4 than in age-matched C4. Side-to-side differences in remobilized rats (E4) were still significant for m_dry and d_app. Additionally, the medullary area was larger, and M_max, M_y, stiffness and work to failure were lower in the right femur than in the left. It is concluded, that the processes of bone deterioration initiated during immobilization do not cease immediately after resumption of normal mechanical loading.     

In vitro effect of KCA-098, a derivative of coumestrol,on bone resorption of fetal rat femurs

The effects of 3,9-bis(N,N-dimethylcarbamoyloxy)-5H-benzofuro[3,2-c]quinoline-6-one (KCA-098), a derivative of coumestrol, on bone resorption was studied in organ cultures of 20-day fetal rat femora. KCA-098 increased the length, dry weight, and calcium and phosphorus contents of parathyroid hormone (PTH)-treated fetal rat femur. As PTH significantly reduced the calcium and phosphorus contents of the femora, probably by stimulating bone resorption, KCA-098 seems to inhibit bone resorption. In fact, KCA-098 inhibited the PTH-induced release of ⁴⁵Ca from pre-labeled fetal rat femora into the medium in organ culture. Coumestrol also inhibited the release of ⁴⁵Ca from bone into the medium. However, KCA-098 did not increase the uterine weight of ovariectomized rats, whereas coumestrol did so. Thus KCA-098 is a unique, new inhibitor of bone resorption that has no estrogenic activity.     

Effects of Feed Supplementation on Mineral Composition,Mechanical Properties and Structure in Femurs of Iberian Red Deer Hinds (Cervus elaphus hispanicus)

Few studies in wild animals have assessed changes in mineral profile in long bones and their implications for mechanical properties. We examined the effect of two diets differing in mineral content on the composition and mechanical properties of femora from two groups each with 13 free-ranging red deer hinds. Contents of Ca, P, Mg, K, Na, S, Cu, Fe, Mn, Se, Zn, B and Sr, Young’s modulus of elasticity (E), bending strength and work of fracture were assessed in the proximal part of the diaphysis (PD) and the mid-diaphysis (MD). Whole body measures were also recorded on the hinds. Compared to animals on control diets, those on supplemented diets increased live weight by 6.5 kg and their kidney fat index (KFI), but not carcass weight, body or organ size, femur size or cortical thickness. Supplemental feeding increased Mn content of bone by 23%, Cu by 9% and Zn by 6%. These differences showed a mean fourfold greater content of these minerals in supplemental diet, whereas femora did not reflect a 5.4 times greater content of major minerals (Na and P) in the diet. Lower content of B and Sr in supplemented diet also reduced femur B by 14% and Sr by 5%. There was a subtle effect of diet only on E and none on other mechanical properties. Thus, greater availability of microminerals but not major minerals in the diet is reflected in bone composition even before marked body effects, bone macro-structure or its mechanical properties are affected.     

The effects of stress on cortical bone thickness in rodents

The right and left femora of three groups of rodents, cold stressed, noise stressed, and heat stressed, were sectioned transversely at the most inferior point of the third trochanter. Cortical bone thickness of the proximal section for all three groups was determined by measuring an enlargement obtained with a Wild stereo microscope with a camera lucida drawing attachment. Cold stressed animals were found to have significantly thinner cortical bone than did controls, noise stressed animals did not differ from controls, and heat stressed animals had thinner cortical bone than did controls. It is concluded that stress may be responsible for the thinner cortex of cold and heat stressed animals, but that other factors may be at work and that it is not possible to tell whether different types of stress act through the same or through different mechanisms.     

Hindlimb unloading has a greater effect on cortical compared with cancellous bone in mature female rats.

This study was designed to determine the effects of 28 days of hindlimb unloading (HU) on the mature female rat skeleton. In vivo proximal tibia bone mineral density and geometry of HU and cage control (CC) rats were measured with peripheral quantitative computed tomography (pQCT) on days 0 and 28. Postmortem pQCT, histomorphometry, and mechanical testing were performed on tibiae and femora. After 28 days, HU animals had significantly higher daily food consumption (+39%) and lower serum estradiol levels (-49%, P = 0.079) compared with CC. Proximal tibia bone mineral content and cortical bone area significantly declined over 28 days in HU animals (-4.0 and 4.8%, respectively), whereas total and cancellous bone mineral densities were unchanged. HU animals had lower cortical bone formation rates and mineralizing surface at tibial midshaft, whereas differences in similar properties were not detected in cancellous bone of the distal femur. These results suggest that cortical bone, rather than cancellous bone, is more prominently affected by unloading in skeletally mature retired breeder female rats.     

The Effects of Melatonin on the Physical Properties of Bones and Egg Shells in the Laying Hen

Laying hens often experience unbalanced calcium utilization which can cause deficiencies in bone and egg mineralization. Because melatonin has been shown to affect bone mineralization in other animals, we examined whether treating hens with melatonin would affect eggshell thickness and improve skeletal performance, thereby reducing skeletal and egg shell defects. Birds were given a diet containing either low (30 µg/kg), medium (300 µg/kg), or high (3 mg/kg) concentrations of melatonin, or control feed through approximately one laying cycle. We examined the weight, length, and strength of egg, femur, tibia, and keel. Hens treated with a high concentration of melatonin showed significant strengthening in their femur and tibia, as measured by maximum force sustained and breaking force, compared to controls. Egg weights from hens treated with melatonin were significantly greater than those from hens that were not treated with melatonin. Conversely, egg shell mass of hens treated with melatonin was significantly lower than those of hens not treated with melatonin. Our data suggest that melatonin may affect the allocation of calcium to bone at the expense of egg shell mineralization.     

The effect of habitat geology on calcium intake and calcium status of wild rodents

Summary Calcium is essential for normal physiological function, reproduction and growth in mammals but its distribution in the natural environment is heterogeneous. Spatial variation in calcium soil content is especially marked in the Peak District, United Kingdom, where both calcium-rich limestone and calcium-poor gritstone rock types occur. Wood mice Apodemus sylvaticus (L) and bank voles Clethrionomys glareolus (Schreber 1780) from limestone areas had significantly higher calcium concentrations in stomach contents and in faeces compared with their counterparts from gritstone areas. Calcium status was assessed from serum calcium concentration, femur weight, ash content of the body, calcium concentration in the femur and body ash. There was no significant difference in serum calcium concentration, femur calcium concentration and body ash calcium concentration between animals from the limestone and the gritstone. However, on the limestone, bank voles, but not wood mice, had significantly heavier femora and a greater proportion of ash in the body compared with their gritstone counterparts.     

The mechanical behaviour of intracondylar cancellous bone of the femur at different loading rates

The compressive properties of human cancellous bone of the distal intracondylar femur in its wet condition were determined. Specimens were obtained from six cadaveric femora and were tested at a strain rate of 0.002, 0.10 and 9.16 sec⁻¹. It was found that the compressive strength decreases with an increasing vertical distance from the joint. The highest compressive strength level was recorded in the posterior medial condyle. Correlations among the mechanical properties, the bulk specimen density and the bone mineral content yield (i) highly significant correlations between the compressive strength and the elastic modulus (ii) highly significant correlations between the compressive strength or the modulus of elasticity and the bulk specimen density (iii) a doubtful correlation between the compressive strength and the bone mineral content. All recorded graphs of the impact loaded specimens displayed several well defined stress peaks, unlike the graphs recorded at low loading rates. It can be concluded that upon impact loading the localized trabecular failure which is associated with each peak, does not affect the spongy bone's stress capacity in a detrimental way.     

Structural strength of the macaque femur

New techniques in bone mechanics, and the demonstration that locomotor function can be interpreted based on patterns of structural strength delineated by these new techniques, lay the foundation for analyses of structural strength in nonhuman primate long bones. The present paper details topographic variability in structural strength of the femoral diaphysis of Macaca as a basis for further quantifying form-function interactions in pronograde primates. The femoral diaphyses of 42 macaques were serially sectioned. These sections were digitized, and coordinate points were submitted to the SCADS computerized stress analysis program. This analysis indicated that the femoral diaphysis of Macaca is better adapted proximally than distally to resist axial loads. The proximal third of the femur is better able to resist bending loads in the posterolateral/anteromedial direction than in the standard planes. The distal femur is geometrically well suited to resist high bending loads, particularly in the mediolateral plane. The elliptical construction of the distal femur is designed to resist high torsional loads as well. When compared with density data on the macaque femoral diaphysis, these data indicate extremely high rigidity in the mediolateral plane. The inverse relationship between density and structural rigidity distally indicates the presence of compensatory mechanisms between structural strength, geometry, and density. Similarities in femoral mechanics in macaques and humans suggest uniformity of stress patterns of the lower extremity in terrestrial quadrupedal and bipedal locomotion.     

Proportions and function of the limbs of glyptodonts

Vizcaíno, S.F., Blanco, R.E., Bender, J.B. & Milne, N. 2010: Proportions and function of the limbs of glyptodonts. Lethaia, Vol. 44, pp. 93–101. This study examines the limb bone proportions and strength of glyptodonts (Xenarthra, Cingulata). Two methods are used to estimate the body mass and location of the centre of gravity of the articulated specimens. These estimates, together with measurements of the femur and humerus, are used to calculate strength indicators (SI). The other long bones of the limbs are used to calculate limb proportion indices that give an indication of digging ability, speed, and limb dominance in armadillos, the glyptodonts’ living closest relatives. The results show that regardless of how the body mass and centre of gravity are calculated, the majority of the glyptodont’s weight is borne by the hindlimbs. The SI calculations show that femora are sturdy enough to bear these loads. The fact that the femora have higher SI than the humerii indicates that sometimes the hindlimbs are required to bear an even greater proportion of the body weight, possibly when rising to a bipedal posture or pivoting on their hindlimbs to deliver a blow with their armoured tail. The analysis of limb proportions indicates that both the hindlimb and the forelimb have proportions that correlate strongly with body mass. This outcome supports the other results, but also shows that forelimbs must be also involved in manoeuvring the glyptodont body. □Glyptodonts, Mammalia, Xenarthra, limbs, strength indicators.     

The physical and mechanical effects of suspension-induced osteopenia on mouse long bones.

The present investigation addresses the extent of tail-suspension effects on the long bones of mice. The effects are explored in both sexes, in both forelimb and hindlimb bones, and in both diaphyseal and metaphyseal/epiphyseal bones. Two weeks of suspension provided unloading of the femora and tibiae and an altered loading of the humeri. Whole-bone effects included lower mass (approximately 10%) and length (approximately 4%) in the bones of suspended mice compared to controls. The geometric and material properties of the femora were considered along the entire length of the diaphysis and in the metaphysis/epiphysis portions as a unit. Geometric effects included lower cross-sectional cortical area (16%), cortical thickness (25%) and moment of inertia (21%) in the femora of suspended mice; these differences were observed in both distal and proximal portions of the femur diaphysis. The relative amount of bone comprising the middle 8 mm of the diaphysis was greater (3%) in the control mice than in the suspended mice. Significant mass differences between the group in the metaphysis/epiphysis were not observed. Material effects included lower %ash (approximately 2%) in the femora and tibiae as well as in the humeri of suspended mice compared to controls. With respect to the measured physical and material properties, suspension produced similar bone responses in male and female mice. The effects of suspension are manifested largely through geometric rather than through material changes.     

The behaviour of microcracks in compact bone

This paper summarises four separate studies carried out by our group over the past number of years in the area of bone microdamage. The first study investigated the manner by which microcracks accumulate and interact with bone microstructure during fatigue testing of compact bone specimens. In a series of fatigue tests carried out at four different stress ranges between 50 and 80 MPA, crack density increased with loading cycles at a rate determined by the applied stress. Variations in the patterns of microdamage accumulation suggest that that at low stress levels, larger amounts of damage can build up without failure occurring. In a second study using a series of four-pont bending tests carried out on ovine bone samples, it was shown that bone microstructure influenced the ability of microcracks to propagate, with secondary osteons acting as barriers to crack growth. In a third study, the manner by which crack growth disrupts the canalicular processes connecting osteocytes was investigated. Analysis of individual cracks showed that disruption of the canalicular processes connecting osteocytes occurred due to shear displacement at the face of propagating microcracks, suggesting that this may play some role in the mechanism that signals bone remodelling. In a fourth in vivo study, it was shown that altering the mechanical load applied to the long bones of growing rats causes microcrack formation. In vivo microdamage was present in rats subjected to hindlimb suspension with a higher microcrack density found in the humeri than the femora. Microdamage was also found in control animals. This is the first study to demonstrate in vivo microcracks in normally loaded bones in a rat model.     

Effects of ethanol on the ultrastructure of the hamster femur

Several previous studies have indicated that chronic ingestion of ethanol exerts harmful effects on bones. However, few data are available concerning the effects of ethanol on the ultrastructure of bone. To further elucidate the effects of ethanol on bone, we studied the morphology of femur in golden hamsters after long-term treatment with ethanol. Six-week-old male hamsters were divided into 4 groups. Ethanol-treated animals were given ethanol at a concentration of 7% with food and water freely available, whereas the pair-fed animals (weight-matched to ethanol hamsters) had tap water available as the only drinking fluid. The femur weight, blood ethanol and serum calcium concentrations were determined after 3 and 5 months. The bone mineral density (BMD) of the whole body was measured before and after the experiment. Femurs of both sides were dissected and processed for morphometric measurement, light microscopy, scanning and transmission electron microscopy. In the ethanol-treated hamsters, BMD of the whole body and the weight of femur tended to decrease when compared with those of the controls. Light microscopy and scanning electron microscopy showed that the trabecula in the distal end of the femur from ethanol-treated hamsters were thinner than those of the controls. We also observed the disrupted swollen mitochondria of the femoral osteoblasts and osteocytes in the ethanol-treated hamsters. No significant difference in serum calcium levels and femoral osteoclasts was found. These results indicate that long-term treatment with ethanol results in disruption of femoral osteoblasts and reduction of bone mass in trabecular bone.     

Femoral stiffness and strength critically depend on loading angle: a parametric study in a mouse-inbred strain

Biomechanical tests of human femora have shown that small variations of the loading direction result in significant changes in measured bone mechanical properties. However, the heterogeneity in geometrical and bone tissue properties does not make human bones well suited to reproducibly assess the effects of loading direction on stiffness and strength. To precisely quantify the influence of loading direction on stiffness and strength of femora loaded at the femoral head, we tested femora from C57BL/6 inbred mice. We developed an image-based alignment protocol and investigated the loading direction influence on proximal femur stiffness and strength. An aluminum femoral phantom and C57BL/6 femora were tested under compression with different loading directions. Both tests, with the aluminum phantom and the murine bones, showed and quantified the linear dependence of stiffness on loading direction: a 5 degrees change in loading direction resulted in almost 30% change in stiffness. Murine bone testing also revealed and quantified the variation in strength due to loading direction: 5 degrees change in loading direction resulted in 8.5% change in strength. In conclusion, this study quantified, for the first time, the influence of misalignment on bone stiffness and strength for femoral head loading. We showed the extreme sensitivity of this site regarding loading direction.     

Different skeletal regional response to continuous brain infusion of leptin in the rat

This study was designed to evaluate whether or not continuous intracerebroventricular infusion of leptin (1.5 microg/rat/24 h, for 28 days) produced different regional response on the skeleton of growing rats. Leptin reduce the accretion of total femoral bone mineral content (BMC) and density (BMD). This effect was related to a reduction of metaphyseal femur as no changes were detected in the diaphysis. Despite the reduced accretion in the volumetric of both femur and tibia compared to controls, leptin had no significant effects on the lumbar vertebrae. Urine deoxypyrydinoline and serum osteocalcin remained more elevated in the leptin-treated group as compared to controls. The results demonstrate that long-term central infusion of leptin activates bone remodeling with a negative balance. Leptin induces distinct responses in the different structure of bone and in the axial and appendicular skeleton.     

Effects of calcium deprivation and orchidectomy on bone composition in the rat.

The effects of calcium deprivation and of orchidectomy, separately and combined, on body growth and bone composition have been examined in mature male rats. Calcium deprivation had no significant effect on the rate of body growth but femoral bone weight, bone ash weight and total calcium and phosphorus contents of the femora were reduced while the water content increased. However, there were no significant changes in the ratio of bone weight to body weight, in the amounts of calcium or phosphorus per unit weight of bone, or in the ratio of calcium to phosphorus in the bone. Orchidectomy reduced the rate of body growth, the mean weight of the femora and the ratio of bone weight to body weight. There was a 60% decrease in bone water and a 30--35% reduction in the calcium and phosphorus content of the femora but the amounts of ash, calcium and phosphorus per unit weight of bone fell by only 6--10%. The combination of orchidectomy and calcium deprivation had no greater effect on body weight, bone weight or bone composition than had orchidectomy alone. It is concluded that calcium deprivation and orchidectomy both cause osteoporosis in mature rats but the effects of orchidectomy are more severe than those of calcium deprivation and there appears to be some demineralization of the bone remaining after orchidectomy.     

Birth is but our death begun: A bioarchaeological assessment of skeletal emaciation in immature human skeletons in the context of environmental,social, and subsistence transition

The second millennium BC was a period of significant social and environmental changes in prehistoric India. After the disintegration of the Indus civilization, in a phase known as the Early Jorwe (1400–1000 BC), hundreds of agrarian villages flourished in the Deccan region of west-central India. Environmental degradation, combined with unsustainable agricultural practices, contributed to the abandonment of many communities around 1000 BC. Inamgaon was one of a handful of villages to persist into the Late Jorwe phase (1000–700 BC), wherein reliance on dry-plough agricultural production declined. Previous research demonstrated a significant decline in body size (stature and body mass index) through time, which is often used to infer increased levels of biocultural stress in bioarchaeology. This article assesses evidence for growth disruption in the immature human skeletal remains from Inamgaon by correlating measures of whole bone morphology with midshaft femur compact bone geometry and histology. Growth derangement is observable in immature archaeological femora as an alteration in the expected amount and distribution of bone mass and porosity in the midshaft cross-section. Cross-section shape matched expectations for older infants with the acquisition of bipedal locomotion. These results support the hypothesis that small body size was related to disruptions in homeostasis and high levels of biocultural stress in the Late Jorwe at Inamgaon. Further, the combined use of geometric properties and histological details provides a method for teasing apart the complex interactions among activity and “health,” demonstrating how biocultural stressors affect the acquisition and quality of bone mass. Am J Phys Anthropol 155:243–259, 2014. © 2014 Wiley Periodicals, Inc.     

Experimental cold modification of cranio-facial morphology

A possible relationship between cranio-facial form and growth under cold stress was investigated through a control group (N=17)—experimental group (N=14) comparison. Two groups of young rats were exposed to 90 days of 22°C and 5°C temperatures respectively. Methods of analysis included measurement of overall bodily dimensions as well as detailed examination of the cleaned, dried skulls and femora. Statistical comparison of the cold and non-cold grown rats showed a number of highly significant mean differences; particularly a narrower nose, rounder neurocranium, and shorter femur was seen in the cold stressed animals. Human anatomical homologs were briefly noted as were their possible genetic and ontogenetic causes.