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Geometric, elastic, and structural properties of maturing rat femora
Abstract
Geometric, elastic, and structural properties of growing rat femora were determined from bending and torsion tests followed by bone sectioning and measurement of areal properties. Rosette strain gages bonded to the bone surface measured the strain during testing. A computer generated elliptical cross-sectional representation of the cross section geometry was used for calculation of material and structural properties. All structural and material properties increased with increasing age, exhibiting age-related changes that were best represented by an allometric or "heterauxic" growth pattern (y = axb) up to maturity. The femoral axial, flexural, and torsional rigidity increased 5.7, 10.1, and 14.8 fold, respectively, during maturation from 21 to 119 days of age. The increase in whole bone rigidity during maturation was caused primarily by changes in geometry. The bone tissue tensile longitudinal elastic modulus and shear modulus approximately doubled, and the shear strength increased approximately fourfold over this same period. Following maturity, a much slower increase in bending and torsional properties was noted. The results suggest that bone structural properties are regulated by changes in both geometric and material properties.
... Strain measurement in vivo 1988. Changes in mechanical properties of rat femora during growth have been reported after in vitro mechanical testing (Vogel 1979, Ekeland 1982, Keller et al. 1986, and recently also by in vivo measurements (Keller and Spengler 1989). ...
... Increased bone stiffness with age was to be expected when testing the bone as a composite structure (Torzilli et al. 1981, Ekeland et al. 1982, Jonsson et al. 1984, Keller et al. 1986. Increased stiffness was also demonstrated when calculated from strain-gauge recordings. ...
... An interesting finding in the present study was that ultimate load continued to increase from 12 to 52 weeks of age, whereas bone strength (maximum bending stress) did not reveal any significant change during this period. A constant level for bone strength has been reported at about 4 months of age in rats (Vogel 1979, Ekeland et al. 1981, Keller et al. 1986). Thus, the increase in load bearing capacity (e.g., the strength of bone as a structure) with age in adults rats must be a result of larger cross-sectional dimensions. ...
Strain gauges were implanted on the anterior surface of the femoral diaphysis of rats aged 6, 12 or 52 weeks. Strain was recorded while the rats were running on a treadmill. The peak strain was of the same magnitude at different animal ages, although there was a somewhat lower value for 52-week-old animals. Stiffness calculated from in vivo strain measurements and from a 3-point bending test on excised femora was correlated: stiffness increased with age. Maximum bending stress increased from 6-12 weeks of age, but then there was no further increase. Ultimate load, on the contrary, increased steadily over the entire 52-week period. This indicates that higher load-bearing capacity with increased age in adult rats is due to increased dimensions of the bone rather than its material properties. The present study demonstrates that conventional in vitro measurements of mechanical properties of bone correspond to measurements of strain during physical activity, and that both are valid measurements of physical properties of bone.
... There is some consensus in the field that the age of rodents is a strong factor in determining the morphologic and mechanical properties of the bones. Rodents go through rapid growth in skeletal structure and bone density from the time of reaching puberty (6-7 weeks) to skeletal maturity (17 to 24 weeks) (Brodt et al., 1999;Keller et al., 1986;Sengupta, 2013;Song et al., 2019). These growths slow down drastically afterward and become insignificant by 12 months of age. ...
... Rat age-related differences in long bone mechanical properties have been reported previously in the compressive strength of segmented femurs (Danielsen et al., 1993) and three-point bending strength of notched femurs (Uppuganti et al., 2016). The influences of age on whole bone mechanical behaviors during the span of adulthood have rarely been reported (Keller et al., 1986). ...
Background
Skeletally mature rodents are frequently used in studies of bone health and bone healing, some of them requiring longitudinal observations that span a significant portion of the animals' adulthood. However, changes in whole bone mechanics associated with the natural aging of adult rats have not been extensively characterized.
Methods
Femurs from skeletally mature Wistar rats in three age groups of 24-week (young adult), 39-week (middle-age), and 54-week (late middle-age) were tested under three-point bending load in the anterior-posterior direction. Mechanical properties and geometric properties of the femurs from the two older groups were compared to the 24-week rats.
Findings
Significantly greater strength, rigidity, and post-yield deformation were found in the 54-week group when compared to the 24-week group. The oldest group also demonstrated greater leg length, anteroposterior width, and cross-sectional moment of inertia over the youngest group. Of the intrinsic properties, the highest ultimate stress was found in the 39-week and was significantly higher than the 24-week group. The ultimate strain increased with age, and the difference between the youngest and the oldest group was statistically significant.
Interpretation
The results suggest that femoral bending properties and geometric properties are continually modified from young adult to late-middle-aged animals. Knowing the baseline bone strength and rigidity throughout adulthood of a rodent breed helps guide animal selection in study design.
... This study performed a head compression test of the right femur extracted from 32-week-old mice and found significant differences in the ultimate load and yield load between the OVX group and the CON group. It was considered that this was the impact of changes in bone mineral density consistent with osteoporosis as Ekeland et al. [26] and Keller et al. [27] reported. However, there was no significant difference in stiffness. ...
A biomechanical test is a good evaluation method that describes the structural, functional, and pathological differences in the bones, such as osteoporosis and fracture. The tensile test, compression test, and bending test are generally performed to evaluate the elastic modulus of the bone using mice. In particular, the femoral head compression test is mainly used for verifying the osteoporosis change of the femoral neck. This study conducted bone mineral density analysis using in vivo microcomputed tomography (micro-CT) to observe changes in osteoporosis over time. It proposed a method of identifying the elastic modulus of the femur in the normal group (CON group) and the osteoporotic group (OVX group) through finite element analysis based on the femoral head compression test and also conducted a comparative analysis of the results. Through the femoral head compression test, it was verified that the CON group’s ultimate and yield loads were significantly higher than those of the OVX group. It was considered that this result was caused by the fact that the bone mineral density change by osteoporosis occurred in the proximal end more often than in the femur diaphysis. However, the elastic modulus derived from the finite element analysis showed no significant difference between the two groups.
... The work to failure, stiffness, ultimate displacement (d), and ultimate force (F) of the femur were calculated from the load-deformation curve. After failure, the cross-sectional area of the femur was calculated as a hollow ellipse [18,21,22]. The major and minor internal and external axes of the crosssectional area were measured by digital caliper (DT-200; Niigata Seiki, Niigata, Japan). ...
Background
The major types of commercially available gelatin hydrolysates are prepared from mammals or fish. Dietary gelatin hydrolysates from mammals were reported to improve bone mineral density (BMD) in some animal models. In contrast, there is limited study showing the effects of dietary gelatin hydrolysates from fish on BMD. The quantity and structure of peptides in the plasma after oral administration of gelatin hydrolysates depend on the gelatin source, which suggests that the biological activity of gelatin hydrolysates depend on the gelatin source. This study examined the effects of fish-derived gelatin hydrolysate (FGH) or porcine-derived gelatin hydrolysate (PGH) intake on BMD and intrinsic biomechanical properties in magnesium (Mg)-deficient rats as a model showing the decrease in both BMD and intrinsic biomechanical properties.
Methods
Four-week-old male Wistar rats were assigned into four groups: a normal group was fed a normal diet (48 mg Mg/100 g diet), a Mg-deficient (MgD) group was fed a MgD diet (7 mg Mg/100 g diet), a FGH group was fed a MgD + FGH diet (5% FGH), and a PGH group was fed a MgD + PGH diet (5% PGH) for 8 weeks. At the end of the study, BMD and intrinsic biomechanical properties of the femur were measured.
Results
The MgD group showed significantly lower Young’s modulus, an intrinsic biomechanical property, and trabecular BMD of the femur than the normal group; however, the MgD diet did not affect cortical BMD and cortical thickness. Both the FGH and the PGH groups showed significantly higher cortical thickness and ultimate displacement of the femur than the normal group, but neither type of gelatin hydrolysate affected Young’s modulus. Furthermore, the FGH group, but not the PGH group, showed significantly higher trabecular BMD than the MgD group.
Conclusions
This study indicates that FGH and PGH increase cortical thickness but only FGH prevents the decrease in trabecular BMD seen in Mg-deficient rats, while neither type of gelatin hydrolysate affect intrinsic biomechanical properties.
... Usually, ex vivo analyses are performed to measure and quantify the regained stiffness of the fracture callus to evaluate healing success or detect differences between different treatment groups. The quality of the newly formed bone is commonly determined by either measuring the callus strength with load-at-failure methods or by evaluating the callus stiffness with non-destructive bending or torsion test set-ups [1,2,3,4,5]. Non-destructive torsional testing is performed in rat [6,7,8,9,10] as well as in mouse experiments [11,12,13,14]. ...
For ex vivo measurements of fracture callus stiffness in small animals, different test methods, such as torsion or bending tests, are established. Each method provides advantages and disadvantages, and it is still debated which of those is most sensitive to experimental conditions (i.e. specimen alignment, directional dependency, asymmetric behavior). The aim of this study was to experimentally compare six different testing methods regarding their robustness against experimental errors. Therefore, standardized specimens were created by selective laser sintering (SLS), mimicking size, directional behavior, and embedding variations of respective rat long bone specimens. For the latter, five different geometries were created which show shifted or tilted specimen alignments. The mechanical tests included three-point bending, four-point bending, cantilever bending, axial compression, constrained torsion, and unconstrained torsion. All three different bending tests showed the same principal behavior. They were highly dependent on the rotational direction of the maximum fracture callus expansion relative to the loading direction (creating experimental errors of more than 60%), however small angular deviations (
... Bone structural properties, such as stiffness and strength, depend on geometry and the material within (Spatz et al., 1996;Jämsä et al., 1998;Brodt et al., 1999;Akhter et al., 2001;Jiang et al., 2005;Schriefer et al., 2005). The simplest approach to determine contributions to a bone's mechanical behavior under a given load configuration is to assume a simplified geometry based on measured bone dimensions (Indrekvam et al., 1991;Keller et al., 1986;Levenston et al., 1994). Medical image-based methods have become increasingly common because they provide accurate section geometry, and distinguish between section and material contributions to structural properties using analytical methods based on classical mechanics (Levenston et al., 1994;Morgan et al., 2009;Nyman et al., 2009;O'Neill et al., 2012). ...
... Durante a vida de uma pessoa, o sistema esquelético ajusta-se para manter as integridades estruturais dos ossos, que no cotidiano está sujeito a várias condições de carregamento mecânico. Conseqüentemente, a resposta estrutural, em parte, deve-se ao passado histórico de cargas impostas sobre o esqueleto e a necessidade presente (Keller et al. 1986). ...
In this paper, we show different parameters estimation forms for multi- ple linear regression model. We used clinical data, where the interest was to
... Based on the literature of the subjec of medical professionals, the results to deliver the application of polyur oil in the design of internal fixators o [1] Keller, T S.; Spengler, D M elastic, and strutural properties of m of Orthopaedic Research, v. 4, p. [2] Ignácio, H; Mazzer, N Utilização nas formas compacta e porosa no pre estudo experimental em cães. Rev. 187-194, 2002. ...
With objective of analyzing the mechanical behavior of the internal fixators of spine and of the bony structure, the pieces and the group were made (it structures bony x internal fixator) with the aid a software of solid modeling. The materials used in the rehearsals had been the titanium, now in the market and a castor oil polyurethane destined to the development of you implant bony.
... During maturation bone tissue continues to develop and its mechanical properties change. Several studies have used animal bone tissue to investigate changes in mechanical behaviour during growing [1][2][3][4][5][6][7][8][9][10][11]. In those studies it was found that strength, stiffness and density increased, while ultimate displacement decreased during maturation. ...
In this study, cortical bone tissue from children was investigated. It is extremely difficult to obtain human child tissue. Therefore, the only possibility was to use bone tissue, free from any lesion, collected from young bone cancer patients. The compressive mechanical behaviour of child bone tissue was compared to the behaviour of adult tissue. Moreover, two hypotheses were tested: 1) that the mechanical behaviour of both groups is correlated to ash density; 2) that yield strain is an invariant. Small parts of the diaphysis of femora or tibiae from 12 children (4-15 years) and 12 adults (22-61 years) were collected. Cylindrical specimens were extracted from the cortical wall along the longitudinal axis of the diaphysis. A total of 107 specimens underwent compressive testing (strain rate: 0.1 s(-1)). Only the specimens showing a regular load-displacement curve (94) were considered valid and thereafter reduced to ash. It was found that the child bone tissue had significant lower compressive Young's modulus (-34%), yield stress (-38%), ultimate stress (-33%) and ash density (-17%) than the adult tissue. Conversely, higher compressive ultimate strain was found in the child group (+24%). Despite specimens extracted from both children and adults, ash density largely described the variation in tissue strength and stiffness (R(2)=in the range of 0.86-0.91). Furthermore, yield strain seemed to be roughly an invariant to subject age and tissue density. These results confirm that the mechanical properties of child cortical bone tissue are different from that of adult tissue. However, such differences are correlated to differences in tissue ash density. In fact, ash density was found to be a good predictor of strength and stiffness, also for cortical bone collected from children. Finally, the present findings support the hypothesis that compressive yield strain is an invariant.
... This raises the possibility that these bone properties could have been influenced by age-related changes that may have masked the effects of hibernation. Bone geometrical properties increase with age in maturing animals (Keller et al., 1986) and skeletal growth can continue even under disuse conditions (Globus et al., 1986;Abram et al., 1988;Biewener and Bertram, 1994), therefore these increasing trends could have influenced the comparisons of hibernating and active juvenile squirrels, masking potential bone loss induced by disuse. However, cortical bone geometrical and mechanical properties did not change over the course of hibernation in the adult squirrels, and importantly, average bone geometrical properties were unexpectedly larger in the adult hibernating compared with adult active squirrels (Table1). ...
Lack of activity causes bone loss In most animals. Hibernating bears have physiological processes to prevent cortical and trabecular bone loss associated with reduced physical activity, but different mechanisms of torpor among hibernating species may lead to differences in skeletal responses to hibernation. There are conflicting reports regarding whether small mammals experience bone loss during hibernation. To investigate this phenomenon, we measured cortical and trabecular bone properties in physically active and hibernating juvenile and adult 13-lined ground squirrels (Ictidomys tridecemlineatus, previous genus name Spermophilus). Cortical bone geometry, strength and mineral content were similar in hibernating compared with active squirrels, suggesting that hibernation did not cause macrostructural cortical bone loss. Osteocyte lacunar size increased (linear regression, P=0.001) over the course of hibernation in juvenile squirrels, which may indicate an osteocytic role in mineral homeostasis during hibernation. Osteocyte lacunar density and porosity were greater (+44 and +59%, respectively; P<0.0001) in hibernating compared with active squirrels, which may reflect a decrease in osteoblastic activity (per cell) during hibernation. Trabecular bone volume fraction in the proximal tibia was decreased (-20%; P=0.028) in hibernating compared with physically active adult squirrels, but was not different between hibernating and active juvenile squirrels. Taken together, these data suggest that 13-lined ground squirrels may be unable to prevent microstructural losses of cortical and trabecular bone during hibernation, but importantly may possess a biological mechanism to preserve cortical bone macrostructure and strength during hibernation, thus preventing an increased risk of bone fracture during remobilization in the spring.
... [35] Buna ra¤men, ke-mikte lineer elastik bir stres-gerilim iliflkisinin kabul edilebilir oldu¤u düflünülmüfltür. [36] Kemi¤in mekanik kuvvetinin geri kazan›m›, iyileflmekte olan k›r›¤›n en önemli klinik görüntüsünü oluflturur. Biyomekanik aç›dan kemik k›r›lganl›¤›n›n ölçütü olarak kemi¤in yük tafl›ma kapasitesi, daya-n›kl›l›¤›, deforme olma özelli¤i, k›r›l›ncaya kadar absorbe etti¤i enerji miktar› say›labilir. ...
We aimed to evaluate the effect of head trauma on fracture healing with biomechanical testing, to compare the results obtained from a femur model created by finite element analysis with experimental data, and to develop a finite element model that can be employed in femoral fractures.
Twenty-two Wistar albino rats were randomized into two groups. The control group was subjected to femoral fracture followed by intramedullary fixation, whereas the head trauma group was subjected to femoral fracture followed by intramedullary fixation along with closed blunt head trauma. Bone sections obtained with computed tomography from rat femurs were transferred into a computer and a 3D mathematical model of femur was created. At the end of week 4, femurs were examined by biomechanical testing and finite element analysis.
The mean maximum fracture load was significantly higher in the head trauma group than in control group (p<0.05). Maximum strain values were also significantly high in the head trauma group (p<0.05). There was no significant difference between the groups with regard to maximum deformation (p>0.05). The head trauma group had significantly higher mean bending rigidity than the control group (p<0.05). The head trauma group showed no significant difference from the control group in terms of strain energy and elasticity module (p>0.05). There was no significant difference between experimental biomechanical test and finite element analysis (p>0.05).
Noninvasive methods such as finite element analysis are useful in examination of the mechanical structure of bones. Experimental biomechanical test and finite element analysis methods suggest that head trauma contributes to fracture healing.
... However, maintenance of the calculated stresses, which are independent of tissue material properties, and tibial stiffness suggest a minor role for the increase in TMD with age in modulating bone stiffness. Additionally, continuum-level and solid phase measures of elastic modulus indicate that modulus does not change significantly following sexual maturation in female rodents (Busa et al., 2005;Keller et al. 1986;Miller et al., 2007;Somerville et al., 2004), which occurs at 4-5wks of age in female mice (Richman et al., 2001;Sheng et al., 1999). Specifically, elastic moduli in female C57Bl/6 tibiae did not change over the age range examined here (Somerville et al., 2004) and bone tissue stiffness in 40 day old BALB/cByJ mice was not significantly different from mature bone despite lower TMD and mineralization levels (Miller et al., 2007). ...
Whole bone morphology, cortical geometry, and tissue material properties modulate skeletal stresses and strains that in turn influence skeletal physiology and remodeling. Understanding how bone stiffness, the relationship between applied load and tissue strain, is regulated by developmental changes in bone structure and tissue material properties is important in implementing biophysical strategies for promoting healthy bone growth and preventing bone loss. The goal of this study was to relate developmental patterns of in vivo whole bone stiffness to whole bone morphology, cross-sectional geometry, and tissue properties using a mouse axial loading model. We measured in vivo tibial stiffness in three age groups (6, 10, 16 wk old) of female C57Bl/6 mice during cyclic tibial compression. Tibial stiffness was then related to cortical geometry, longitudinal bone curvature, and tissue mineral density using microcomputed tomography (microCT). Tibial stiffness and the stresses induced by axial compression were generally maintained from 6 to 16 wks of age. Growth-related increases in cortical cross-sectional geometry and longitudinal bone curvature had counteracting effects on induced bone stresses and, therefore, maintained tibial stiffness similarly with growth. Tissue mineral density increased slightly from 6 to 16 wks of age, and although the effects of this increase on tibial stiffness were not directly measured, its role in the modulation of whole bone stiffness was likely minor over the age range examined. Thus, whole bone morphology, as characterized by longitudinal curvature, along with cortical geometry, plays an important role in modulating bone stiffness during development and should be considered when evaluating and designing in vivo loading studies and biophysical skeletal therapies.
... All of these studies therefore emphasize the importance of mineralization for mechanical properties of bone. Torzilli et al. (1981) reported from a canine bone study that geometry and material contributed cqudly to structural changes, whereas others have reported that structural properties of rat bones are dependent on the geometry to a greater extent than on the material (Ekeland et al. 1981, Keller et al. 1986). ...
We have explored previous findings of remarkably stable in vivo strain at the femoral surface in rats at different ages, and at the same time increased bone stiffness. The rate of collagen synthesis (14C-hydroxyproline/total hydroxyproline ratio) decreased with age, whereas mineralization (calcium/hydroxyproline ratio) increased. Smaller amounts of immature collagen, caused by reduced synthesis, and increased mineralization both probably produce a less flexible material. These chemical alterations support the observed increase in structural stiffness and strength with age. Both mineralization and configurations separately seemed to have effects on in vivo strain. However, none of these variables seemed to be the major determinant for strain.
... where UJf is bending failure stress, M is the bending moment at which failure occurred, c is the distance from the centroid of the cross-section to the periosteal surface, and I is the moment of inertia (Turner and Burr, 1993). The value for moment of inertia used in stress analysis was calculated under the assumption that the femoral cross-sections were elliptical (Keller et al., 1986), ...
In response to recent concerns about the effect of water fluoridation on hip fracture rates, we studied the influence of fluoride intake on bone strength. Four groups of rats were fed a low-fluoride diet ad libitum and received 0, 5, 15, or 50 ppm of fluoride in their drinking water. Animals were euthanized after 3, 6, 12, or 18 months of treatment. Mechanical strength of the right femur was measured by three-point bending. Fluoride content for the left femur was measured, and static histomorphometric measurements were made on a lumbar vertebra. Femoral failure load was not significantly decreased in rats treated for 3 and 6 months, but was decreased as much as 23% in rats treated 12 and 18 months at 50 ppm fluoride. Extrapolation from regression equations predicted that older rats lose 36% of femoral bone strength when bone fluoride content is increased from 0 to 10,000 ppm, while younger rats will lose only 15%. Thus, the decreased strength appeared to be due to the combined effects of fluoride intake and age on bone tissue and was not associated with a decrease in bone density or mineralization defects. There were only small effects of fluoride on bone histomorphometry. Fluoride intake at high levels had no negative effects on bone mineralization. Fluoride intake was associated with slight increases in trabecular bone volume and trabecular thickness, but these effects could not be demonstrated consistently. The mechanism by which large amounts of fluoride affect bone strength more severely in older animals is unknown.
... In our study, the lack of significant differences in both femoral and vertebral dimensions would indicate that neither longitudinal nor radial bone growth were affected. Given these results, and the fact that ALN therapy was initiated during the accelerated growth phase of both femora and lumbar vertebrae of the rat (23,(36)(37)(38), we surmise that the increased ultimate load seen in those groups receiving ALN may be explained in part by the use of antiresorptive therapy during skeletal growth, reSUlting in an increased peak bone mass. Though the application of ALN during skeletal growth would appear beneficial and introduces a somewhat novel and intriguing idea. ...
Alendronate (4-amino-1-hydroxybutylidene bisphosphonate) is a novel amino bisphosphonate that is being developed for the treatment of osteolytic bone disorders such as osteoporosis. As part of a 2-year carcinogenicity study, we investigated the morphologic and biomechanical effects of long-term alendronate (ALN) therapy, given throughout skeletal growth, maturation, and aging, on rat vertebrae and femora. Three treatment groups, receiving either deionized water, low- (1.00 mg/kg), or high-dose (3.75 mg/kg) ALN, were given daily oral treatment for 105 weeks. Results from mechanical tests indicate that ALN therapy (in males) increased the vertebral ultimate compressive load by 96% in the high- and 51% in the low-dose groups when compared with controls. ALN similarly increased the male ultimate femoral bending load by 59% in the high- and 31% in the low-dose groups. Vertebrae and femora from female rats treated with both high- and low-dose ALN also failed at significantly higher loads than controls, but no differences were seen between low- and high-dose groups. Morphologic analysis of both male and female vertebrae revealed a dose-dependent increase in area fraction of bone. Rats receiving high-dose ALN had a greater area fraction of bone than those receiving low doses. Both groups were greater than controls. Thus, the administration of ALN resulted in increased femoral cortical bending load when compared with control animals, as well as increased vertebral ultimate compressive load commensurate with a dose-related preservation of vertebral bone.(ABSTRACT TRUNCATED AT 250 WORDS)
... The precise and reproducible placement of the strain gauges between the left and righ femora was essential to obtaining accurate results. Keller et al. (1986)'' found that a 5" mounting error for a single element strain gauge could result in up to a 10 percent error in the strain values. Szivek et al. (1992) 14 have noted that in vivo strains change 11 p strain per centimeter along the length of greyhound femora. ...
In many studies, bone healing and remodeling have been examined in various animal models using one femur as a control for the contralateral femur based on the assumption that they are bilaterally symmetrical. Symmetry studies have been limited mainly to geometrical properties. The purpose of this study was to determine whether or not there is symmetry in the mechanical properties of rat femora. Two strain gauges were attached to the anterior surface parallel to the long axis of explanted femora of retired female breeder and 120-day-old male Sprague Dawley rats. Femora were mechanically tested in cantilever bending and the strain values were recorded. Moments of inertia, cortical areas, and moduli of elasticity were determined from strains and cross-sectional properties. Female femora showed a bilateral strain difference of less than 2.2% and an elastic modulus difference of less than 8.7%. Males had less than 2.0% and 7.9% differences for strain and elastic moduli, respectively. Statistical analysis showed no significant difference between left and right femoral strain values for the females, but modulus differences were significant different at the p = 0.05 level. There was no significant difference in strain and modulus values for the males, indicating mechanical and geometrical symmetry of their femora.
Description
Discusses the biomechanics of skiing and skiing injuries; the relationship of skies, ski boots, and ski release bindings to injuries; cross-country skiing injuries; epidemiology of alpine skin injuries; cold injuries; injury treatment; rescue and first aid practices and equipment; and standards for safety.
Efforts to promote sustainable production and processing of Ruspolia differens Serville (Orthoptera: Tettigoniidae) as a viable agribusiness model for enhancing food and nutrition security have gained momentum. However, the inexistence of rearing techniques adapted to this insect creates uncertainty regarding the effectiveness of up-scaling production. This study evaluated the effect of five temperatures (26, 28, 30, 32 and 34 °C) on egg development time, percentage hatchability and nymphal weight at hatching. It also evaluated the average weekly wet weight attained by R. differens and percentage survival during growth when reared at 30 °C on four different food plant diets. The diets composed of (1) star grass Cynodon dactylon (L.) Pers.; (2) wild millet Eleusine indica (L.) Gaertn.; (3) guinea grass Panicum maximum Jacq.; and (4) a mixture of the three food plants. The highest hatchability (89.33±3.06%) was observed for egg clusters that were not detached from the leaf sheaths and incubated at 30 °C. At the same temperature, the hatchability of eggs detached from the leaf sheath was 43.33±4.16%. The wet nymphal weight at hatching varied significantly across the different incubation temperatures. For eggs that were not detached from the leaf sheath, it ranged between 3.12±1.20 mg at 30 °C to 4.15±0.98 mg at 34 °C, while for eggs that were detached, it ranged between 2.96±1.14 at 32 °C to 6.0±2.0 mg at 26 °C. The highest wet nymphal weight (586.4 mg) and growth rate (10.47 mg/day) of adult R. differens after 8 weeks was recorded on wild millet, followed by the mixture of the three food plants (553.7 mg; 9.9 mg/day). Food plants significantly influenced survival of nymphs, with C. dactylon and P. maximum associated with the highest survival rate (53.3%). These findings are central to upscaling R. differens production.
The purpose of this study was to determine the efficacy of human parathyroid hormone, hPTH (1–34), in augmenting cortical bone mass in ovariectomized (OVX) growing rats. Thirty 11-week-old female Sprague-Dawley rats were divided into five groups of six animals each. Ovariectomy was performed on 18 rats and 12 rats were subjected to sham surgery. All rats were left untreated for the 4 weeks postsurgery. At the end of pretreatment period, groups of baseline sham (Group 1) and OVX (Group 2) rats were killed. The remaining rats were divided into three groups and each treated as follows. Sham-operated rats (Group 3) and ovariectomized rats (Group 4) were injected with saline vehicle. Ovariectomized rats (Group 5) were injected with hPTH (1–34), 30jLlg/kg, five times per week. All treatments were initiated at 4 weeks postsurgery for a 4-week period. To classify the effects of PTH on cortical bone modeling and remodeling during the treatment period, the PTH-treated group was injected subcutaneously with Oxytetracycline just prior to the initiation of the PTH treatment. All animals were double-labeled with subcutaneous injections of calcein on day 6 and day 2 before euthanization. Cross sections of the tibial diaphysis were subjected to quantitative bone histomorphometry. PTH treatment of OVX rats (Group 5) increased cortical bone area and width, tended to decrease the bone marrow area, and did not significantly increase the endocortical resorbing surface compared to the vehicle-treated OVX rats. PTH administration in the OVX rats increased cortical bone by the addition of new circumferential bone on both the periosteal and endocortical surfaces by stimulating osteoblastic recruitment; the newly formed bone was lamellar in nature. PTH administration activated cortical bone modeling in the formation mode (activation-formation) on either the periosteal or endocortical envelopes. The present data indicate that PTH stimulated cortical bone modeling in the formation mode and augmented cortical bone mass in the tibial diaphysis of OVX rats. These findings are in agreement with previous observations that dogs and humans respond similarly to PTH, suggesting that PTH administration may be a useful anabolic agent in the prevention and treatment of postmenopausal osteoporosis.
This chapter reviews the methods commonly used for biomechanical evaluation of bone or bone replacement materials and substantially expands upon the authors’ previous review of biomechanical test methods. 1 It is assumed that the reader has a basic understanding of skeletal anatomy and mechanics of materials (these topics are covered in Chapter 1, Integrated Bone Tissue Physiology, by Jee and Chapter 6, Mechanics of Materials, by Cowin). There are a wide variety of experimental techniques available for evaluation of bone structure, microstructure, and biomechanics. Many of these are described in detail in other chapters. Techniques not covered in this chapter but covered elsewhere in the book include measurement of bone structure and mineral density using X-ray techniques (Chapter 9 by Rüegsegger and Chapter 34 by Kaufman and Siffert), quantification of trabecular structure (Chapter 14 by Odgaard), measurement of microdamage (Chapter 17 by Jepsen, Davy, and Akkus), measurement of in vivo bone strains (Chapter 8 by Fritton and Rubin), and measurement of viscoelastic properties of bone (Chapter 11 by Lakes).
This is a comprehensive and accessible overview of what is known about the structure and mechanics of bone, bones, and teeth. In it, John Currey incorporates critical new concepts and findings from the two decades of research since the publication of his highly regarded The Mechanical Adaptations of Bones. Crucially, Currey shows how bone structure and bone's mechanical properties are intimately bound up with each other and how the mechanical properties of the material interact with the structure of whole bones to produce an adapted structure. For bone tissue, the book discusses stiffness, strength, viscoelasticity, fatigue, and fracture mechanics properties. For whole bones, subjects dealt with include buckling, the optimum hollowness of long bones, impact fracture, and properties of cancellous bone. The effects of mineralization on stiffness and toughness and the role of microcracking in the fracture process receive particular attention. As a zoologist, Currey views bone and bones as solutions to the design problems that vertebrates have faced during their evolution and throughout the book considers what bones have been adapted to do. He covers the full range of bones and bony tissues, as well as dentin and enamel, and uses both human and non-human examples. Copiously illustrated, engagingly written, and assuming little in the way of prior knowledge or mathematical background, Bones is both an ideal introduction to the field and also a reference sure to be frequently consulted by practicing researchers.
Bone in vivo stresses and moments were determined from rosette strain recordings obtained from the mid-diaphysis of growing exercising rats. Two activity groups were examined beginning at 3 weeks of age: 2 min day −1 and 45 min day −1 at 0.2 m s −1 in an exercise wheel. In vitro moment-strain curves were obtained during mechanical calibration tests on intact femora, and area inertial properties were determined from the mid-diaphysis cross-sections. The mechanical calibration and histomorphometry procedures were then used to compute functional stresses and moments based on the in vivo rosette strain recordings. During the period 6–30 weeks of age the rats increased in body weight over threefold, but no significant changes in principal strain and stress magnitude or orientation were found. Peak in vivo compressive and tensile moments increased during growth in proportion to the animal mass squared, but the ratio of these moments to animal body weight times bone length ( BWBL ) remained constant throughout growth and in the adult. The parameter BWBL appears, therefore, to be a useful predictor of long bone functional strength. Peak torsional moments remained a constant 8.1 ± 3.0% of the ultimate torsional strength, providing a safety factor of approximately 12. Differences in the in vivo moments between the two activity groups were found, which were due primarily to adaptive, but not significant, changes in bone geometry. These findings support the hypothesis that long bones model and remodel during growth and altered activity in order to regulate the functional strains at a predefined level.
While much has been learned about the mechanisms of metastatic spread of cancer to bone, there has been little headway in establishing guidelines for monitoring the alteration in bone quality and estimating fracture risk. The aims of this study are, therefore, 1) to evaluate bone quality induced by metastatic bone tumor by analyzing the characteristics on bone microarchitecture and degree of bone mineralization and 2) analyze fracture risk increased secondary to the bone quality changes by metastatic bone tumor through calculating mechanical rigidities based on in-vivo micro CT images. For this study, eighteen female SD rats (12 weeks old, approximate 250 g) were randomly allocated in Sham and Tumor groups. W256 (Walker carcinosarcoma 256 malignant breast cancer cell) was inoculated in the right femur (intraosseous injection) in Tumor group, while 0.9% NaCl (saline solution) was injected in Sham group. The right hind limbs of all rats were scanned by in-vivo micro-CT to acquire structural parameters and degree of bone mineralization at 0 week, 4 weeks, 8 weeks, and 12 weeks after surgery. At the same time, urine was collected by metabolic cages for a biochemical marker test in order to evaluate bone resorption. Then, bone metastasis had been directly identified by positron emission tomography. Finally, axial, bending and torsional rigidities had been calculated based on in-vivo micro CT images for predict fracture risk. The results of this study showed that metastatic bone tumor might induce significant decrease in bone quality and increase of fracture risk. This study may be helpful to monitoring a degree of bone metastasis and predicting fracture risk due to metastatic bone tumor. In addition, this noninvasive diagnostic methodology may be utilized for evaluating other bone metabolic diseases such as osteoporosis.
Resumo - Com o objetivo de analisar o comportamento biomecânico de fixadores internos da coluna vertebral e da estrutura óssea, foram confeccionados as peças e o conjunto (estrutura óssea X fixador de coluna) com o auxílio de um software de modelagem de sólidos. Os materiais utilizados nos ensaios foram o titânio, atualmente no mercado, e um polímero derivado do óleo de mamona destinado ao desenvolvimento de implantes ósseos. Os resultados serão comparados aos modelos experimentais simulados em uma máquina universal de ensaios. Palavras-chave : óleo de mamona, fixadores internos da coluna vertebral, simulação computadorizada. Abstract - With the objective of analyze the way of biomechanical fixators internal spine and bone structure, were made parts and whole (bone structure X fixing column) with the help of a software modeling of sound. The materials used in the tests were the titanium, currently on the market, and a polymer derived from the castor oil for the development of bone implants. The results will be compared to experimental models simulated on a universal testing machine.
The contribution of muscle contraction to the structural capacity of the lower leg has been studied in skeletally immature and mature rats. The right lower legs of both young and adult rats were fractured in 3-point ventral cantilever bending during electrically induced muscle contraction. The left tibiae were dissected free of all soft tissues and tested as controls. The ultimate bending moment increased 73% in young and 84% in adult rats, compared with the control tibiae. The ultimate energy absorption increased 149% and 302% in the young and adult rats, respectively. Ultimate deflection increased 70% and 140%, whereas bending stiffness decreased 18% and 24% in the young and adult rats, respectively. The results show that the fracture mechanics in vivo are different in the immature and mature skeleton. This finding is discussed in relation to the differences in tibial fracture incidence in young and adult alpine skiers.
A refinement of the current ultrasonic elasticity technique was used to measure the orthotropic elastic properties of rat
cortical bone as well as to quantify changes in elastic properties, density, and porosity of the dwarf rat cortex after a
treatment with recombinant human growth hormone (rhGH). The ultrasonic elasticity technique was refined via optimized signal
management of high-frequency wave propagation through cubic cortical specimens. Twenty dwarf rats (37 days old) were randomly
assigned to two groups (10 rats each). The dwarf rat model (5–10% of normal GH) was given subcutaneous injections of either
rhGH or saline over a 14-day treatment period. Density was measured using Archimedes’ technique. Porosity and other microstructural
characteristics were also explored via scanning electron microscopy and image analysis. Statistical tests verified significant
decreases in corticla orthotropic Young’s (−26.7%) and shear (−16.7%) moduli and density (−2.42%) concomitant with an increase
in porosity (+125%) after rhGH treatments to the dwarf model (p<0.05). A change in material symmetry from orthotropy toward planar isotropy within the radial-circumferential plane after
GH treatments was also noted. These results demonstrate some alteration in bone properties at this time interval. Structural
implications of these changes throughout physiological loading regimens should be explored.
Inactivity causes bone loss, and a remobilization period that is 2–3 times longer than the disuse period is required to recover lost bone. Black bears (Ursus americanus), however, experience annual disuse (hibernation) and active periods that are approximately equal in length, but maintain bone material properties with age. Here, the effects of annual hibernation periods on whole bone properties were investigated. This study shows that mineral, geometrical and whole bone mechanical properties increase with age in black bear femurs, whereas porosity decreases with age. These results provide further support that black bears possess a biological mechanism to avoid disuse osteoporosis.
In this study we describe the use of ultrashort echo time (UTE) magnetic resonance imaging (MRI) to evaluate short and long T2* components as well as the water content of cortical bone. Fourteen human cadaveric distal femur and proximal tibia were sectioned to produce 44 rectangular slabs of cortical bone for quantitative UTE MR imaging, microcomputed tomography (µCT), and biomechanical testing. A two-dimensional (2D) UTE pulse sequence with a minimal nominal TE of 8 µseconds was used together with bicomponent analysis to quantify the bound and free water in cortical bone using a clinical 3T scanner. Total water concentration was measured using a 3D UTE sequence together with a reference water phantom. UTE MR measures of water content (total, free, and bound), T2* (short and long), and short and long T2* fractions were compared with porosity assessed with µCT, as well as elastic (modulus, yield stress, and strain) and failure (ultimate stress, failure strain, and energy) properties, using Pearson correlation. Porosity significantly correlated positively with total (R(2) = 0.23; p < 0.01) and free (R(2) = 0.31; p < 0.001) water content as well as long T2* fraction (R(2) = 0.25; p < 0.001), and negatively with short T2* fraction and short T2* (R(2) = 0.24; p < 0.01). Failure strain significantly correlated positively with short T2* (R(2) = 0.29; p < 0.001), ultimate stress significantly correlated negatively with total (R(2) = 0.25; p < 0.001) and bound (R(2) = 0.22; p < 0.01) water content, and failure energy significantly correlated positively with both short (R(2) = 0 30; p < 0.001) and long (R(2) = 0.17; p < 0.01) T2* values. These results suggest that UTE MR measures are sensitive to the structure and failure properties of human cortical bone, and may provide a novel way of evaluating cortical bone quality.
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.
Fluoride from fluoridated water accumulates not only in the enamel of teeth but also in the skeleton. The effects of fluoridated water on the skeleton are not well understood, yet there is some evidence that fluoridated water consumption increases the incidence of fractures. In the present study, femoral bending strength was measured in rats on fluoride intakes that ranged from low levels to levels well above natural high fluoride drinking water. Bone strength followed a biphasic relationship with bone fluoride content. Fluoride had a positive effect on bone strength for lower fluoride intakes and a negative influence on bone strength for higher fluoride intakes. The vertebral fluoride content at which femoral strength was maximum was between 1,100 and 1,500 ppm. The increase in femoral strength at this fluoride level was not accompanied by an increase in femoral bone density. The optimal fluoride content is within the range of bone fluoride contents found in persons living in regions with fluoridated water (1 ppm) for greater than 10 years.
Nine‐month‐old female rats were subjected to right hindlimb immobilization or served as controls for 0, 2, 10, 18, and 26 weeks. They were double‐labeled with bone markers prior to sacrifice. Experimental unloading was produced by immobilizing the right limb against the abdomen with an elastic bandage. Single‐photon absorptiometry was performed on the intact femurs; static and dynamic histomorphometry were performed on 20‐μm thick toluidine blue‐stained, undecalcified cross sections of the tibial shafts. Changes in the continuously immobilized tibiae were compared to those in both tibiae of age‐matched controls.
Unloading shut off nearly all periosteal bone formation and accelerates bone marrow expansion over that which occurs in age‐related controls. The effects of unloading appeared to be mediated by recruiting fewer osteoblasts which showed inhibited activity. Furthermore, unloading increased endocortical percentage eroded surface. These histological changes lowered cortical bone mass by inhibiting diaphyseal cross sectional expansion and enlarging the bone marrow cavity. The results support Frost's suggestion that decreased mechanical usage depresses bone modeling‐dependent bone gain by decreasing activation of modeling in the formation mode. It also stimulates bone remodeling‐dependent bone loss by increasing activation of remodeling in the resorption mode.
Twenty-four male rats, aged 12 weeks, were subjected to approximately 20,000 loading cycles per day of treadmill running (2 h/day, 26.8 m/min and 10% gradient) for 5 (group A) and 10 days (group B); with corresponding controls (C5) and (C10). Rats in groups B and C10 were given weekly doses of tetracycline from 4 days prior to training. Following training, right tibiae and femora were tested to failure in torsion at 180 degrees/s. Sections were cut from the distal, mid and proximal diaphysis of left bones, bulk-stained in basic fuchsin and two transverse sections (50 microns) were cut and examined for the presence of microdamage and fluorescence. Results for mechanical testing showed a significant reduction in stiffness of tibiae (P less than 0.01) for groups A and B and a significant increase in twist angle (P less than 0.01) for group A when compared with controls. No evidence of microdamage was observed from histological analysis. But, labelling demonstrated reduced appositional growth of the periosteal and endosteal surface at the mid-diaphysis of exercised tibiae (P less than 0.01). These tibiae also showed fewer regions of, measurable, appositional growth than controls (P less than 0.05). Exercised femora showed increased appositional growth at the endocortical surface of the mid-diaphysis (P less than 0.05). Reductions in stiffness of exercised tibiae were significantly correlated with cross-sectional area.
We present a noninvasive, in vivo model for strain application in the tibiae of rats. The hind limb of each animal was placed into a device that applied four point bending to the tibia. Bending was applied in the medial-lateral direction causing compression on the lateral surface of the tibia and tension on the anteromedial surface. The peak strain magnitudes were estimated to be between 1600 and 3500 mu strain. In this pilot work, data were collected from 12 rats. The rats received either one cycle per day, four cycles per day, 12 cycles per day, 36 cycles per day, or 108 cycles per day of bending. The experimental (right) tibiae from all of the rats showed new bone formation after 12 days. The control (left) tibiae showed no new bone formation over this period. A better organized, dense bony reaction occurred in regions of lesser strains than in regions of higher strains, where there was a large accumulation of bone easily identified as woven. The organization and density of the newly formed bone appeared to be inversely related to the peak strains in the region. After 40 days of daily loading, the new bone area appeared to be more compact and better mineralized. However, bone formation was still occurring after 40 days. The results of this study suggest that woven bone formation occurred due to the bending stimulus and not due to pathology.
Tibiae from 60 male Wistar rats, aged 13 +/- 1 weeks, were divided into six groups for mechanical and histological testing. Bones were loaded repetitively in torsion at 90 deg.s-1. Group 1 was subjected to 5,000 loading cycles at a twist angle of 3.6 degrees, groups 2-5 to 10,000 cycles at 3.6, 5.4, 7.2, and 9.0 degrees, respectively, and group 6 was tested to failure. Six transverse sections from the middiaphysis were then cut, bulk-stained in basic fuchsin, and hand ground to 30-50 microns to examine the presence of microcracks. Cracks were classified as running parallel to lamellae, crossing lamellae, crossing the full thickness of the cortex, or invading vascular canals. Results for fatigue testing showed that the tibiae exhibited a gradual decrease in torque (P less than 0.05), average stress (P less than 0.01), stiffness (P less than 0.01) and energy absorbed (P less than 0.01) from the initial loading cycle. Analysis of microdamage showed an increase in the variety of cracks from groups 1-5. Analysis of deviance demonstrated a strong dependence of crack probability on the level of loading for all crack types (P less than 0.05) except those crossing lamellae. This study reinforces the evidence that yielding of bone observed during repetitive loading is caused by diffuse structural damage such as microcracking or debonding.
Histomorphometric and biomechanical changes in bone resulting from hypogravity (simulated weightlessness) were examined in this study. Using a head-down hindlimb suspension model, three groups of six male rats underwent simulated weightlessness for periods of one, two and three weeks while a fourth recovery group was suspended for two weeks followed by two weeks of normal activity. Biomechanical data were collected during static and dynamic bending and torsion tests on intact femora. Histomorphometric values were determined from midshaft bone cross sections and material properties were obtained using ash and calcium assays. The experimental groups exhibited significantly lower geometric and material properties than the controls, resulting in structural hypotrophy; geometric and material changes contributed equally to the structural changes. Recovery following a return to normal activity was indicated, although full recovery may take longer than the weightlessness period. In the rat, altered maturation and reduced bone strength were the sequelae of weightlessness.
This study was designed to examine the renal and bony metabolic responses to urinary diversion through intestinal segments. Twenty rats underwent urinary diversion by ureterosigmoidostomy and were compared to twenty control rats with respect to renal excretion of electrolytes and bone mineralization after a 10-week period. Ureterosigmoidostomy rats demonstrated increased renal excretion of ammonium, sulfate, magnesium, and possibly phosphorus. Bone calcium content was decreased in ureterosigmoidostomy rats, while bone phosphorus content was slightly increased. These changes occurred in the absence of systemic acid-base alterations. We are unable to demonstrate an increased renal loss of calcium in the ureterosigmoidostomy rats compared to controls. This suggests that decreased renal reabsorption of urinary calcium is not the primary pathophysiologic process involved in this problem.
To gain some insight into the early effects of spaceflight on skeletal metabolism, we quantified the major chemical constituents and a noncollagenous protein, osteocalcin, in the third-lumbar vertebrae and humeri from 8-wk-old rats that were part of the 7-day NASA Spacelab 3 flight experiments. The ratio of calcium to hydroxyproline in the humeral diaphysis increased from 8.5 in preflight to 9.8 in ground simulation control and only to 8.9 in flight bones. There was no demonstrable change in the fraction of nonmineralized collagen. Osteocalcin content was reduced in the humerus and vertebra. Reduced accumulation of mineral and osteocalcin with no associated decrease in collagen in flight animals suggests that both mineralization and collagen metabolism are impaired in growing animals during spaceflight within a few days after launch. Strength tests of the humeri of flight rats showed substantial deficits that appeared to be related, not only to the reduced bone mass, but also to the composition and quality of new bone formed.
Growth, functional adaptation, and torsional strength were examined in the femora of 39-day-old male Sprague-Dawley rats subjected to hindlimb suspension for 0, 1, 2, 3, or 4 weeks and were compared with measurements for age-matched control animals. Our goal was to understand the effect of reduced loading on the normal age-related changes in femoral properties during growth. The control animals exhibited growth-related increases in all geometric and torsional properties of the femur. The mean body mass and femoral length of the hindlimb-suspended rats were similar to those of the controls throughout the experiment. Over 4 weeks, the femoral cross-sectional and torsional measurements from the hindlimb-suspended rats demonstrated increases in comparison with the basal values (+33% cross-sectional area, +64% polar moment of inertia, +67% ultimate torque, and +181% torsional rigidity), but the age-matched controls showed significantly greater growth-related increases (+71% cross-sectional area, +136% polar moment of inertia, +127% ultimate torque, and +367% torsional rigidity). The differences in femoral structural strength between the hindlimb-suspended animals and the age-matched controls were attributable to differences in altered cross-sectional geometry.
Structural tests, such as whole bone torsion tests, have become widely accepted methods for assessing average bone material properties. To simplify interpretation of these tests, the nonuniform bone geometry is often analyzed as a tube with a constant cross section (prismatic) and the areal properties of the smallest bone section. This approach may not adequately represent the true torsional behavior of the cross section and does not account for any lengthwise variations in bone geometry. The errors introduced by these approximations are particularly significant when comparing bones of different sizes and geometries. In this paper, we examine the effects of approximating the cross-sectional torsional behavior and of neglecting lengthwise variations in bone geometry. We then present a simple, standardized procedure utilizing a FORTRAN computer program for accurate determination of material properties. We examine first simple idealized bone geometries and then a complex three-dimensional model of the femur from a 26-day-old male Sprague-Dawley rat. For these models, the conventional methods for interpreting torsion tests introduce errors of up to 42% in the shear modulus and up to 48% in the maximum shear stress; a straightforward extension of these methods reduces the errors to within 3%.
Pregnancy and lactation are known to cause structural and mechanical changes in bone, but the effects of pregnancy alone have not been evaluated thoroughly. This study used radiographic measurements, torsion testing, mineral analyses, and histological evaluation to determine whether there are changes in bone material and geometric properties during pregnancy in the growing rat, as implied by earlier biochemical and histological studies. The bones of pregnant 9 to 12-week-old rats and controls that were not pregnant and were matched by age (but not weight) were evaluated at times corresponding to 5, 10, 15, and 20 days of the 23-day gestation period to address the following questions: (a) How is the growth of whole bone affected by pregnancy in the growing rat (as determined by radiographic analyses)? (b) How are the mechanical properties (structural and material) of whole bone affected by pregnancy (as assessed by torsion testing)? (c) Are there changes in the characteristics of bone mineral during pregnancy (as determined by measurement of mineral content and x-ray diffraction analyses)? and (d) Are there detectable morphological or ultrastructural differences between the bones of pregnant and control rats (as assessed by analyses based on histology and back-scattered electron imaging)? The presence of statistically significant differences in this study was determined initially on the basis of a two-factor analysis of variance. In general, significant differences were noted only at late gestation (day 20), when the bones were longer and had a greater outer radius and cortical thickness; this indicates that more growth occurred during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)
The present study assessed the contributions of feeding changes and unloading to the overall measured effects of 2-wk hindlimb (Tail) suspension on the mouse femora. Feeding changes were addressed by considering the effects of matched feeding among suspended and control mice. The effects of hind limb unloading were considered by comparing suspended mice to mice equipped identically (though not suspended) and matched-fed. The feeding and unloading aspects of suspension appear to cause distinctly differing effects on the stereotypic modeling of the femora. Matched-feeding was accompanied by increased resorption surface in comparison to suspended mice, while unloading led to reduced bone formation at the mid-diaphysis of the femora. Reduced mineral content was observed in the bones of suspended mice when compared to the other mice groups, but without increased resorption surface. Thus, the unloading aspects of the antiorthostatic suspension protocol apparently causes reduced formation and mineralization in the femur.
Although bone densitometry is often used as a surrogate to evaluate bone fragility, direct biomechanical testing of bone undoubtedly provides more information about mechanical integrity. Like any other specialized field, biomechanics contains its own techniques and vocabulary. This article serves as a guide to biomechanical principles and testing techniques for bone specimens.
The Hyp mouse is an established animal model of X-linked hypophosphatemia, one of the most common genetic forms of metabolic bone disease in humans. This study describes the first determination of whole bone mechanical behavior in the heterozygous male and female Hyp mouse. Femora from 12-week-old mice were tested in torsion. The contribution of structural and material properties to mechanical behavior was determined by geometrical evaluation prior to testing and by analysis of the diaphyseal mineral after testing. The male and female Hyp femora were found to undergo significantly more angular deformation at failure than the same sex normal femora (82.49 +/- 24.37 vs. 22.63 +/- 8.02 rad/m [corrected] for the females and 128.90 +/- 37.05 vs. 22.79 +/- 7.24 rad/m [corrected] for the males) and to have a significantly lower structural stiffness (0.373 +/- 0.130 x 10(-3) vs. 1.33 +/- 0.380 x 10(-3) [corrected] [N-m/(rad/m)] for the females and 0.167 +/- 0.104 x 10(-3) vs. 1.60 +/- 0.502 x 10(-3) [corrected] [N-m/(rad/m)] for the males). The male Hyp femora had a significantly lower failure torque than male normal femora (1.58 +/- 0.62 x 10(-2) vs. 3.44 +/- 1.57 x 10(-2) N-m). Because the polar movement of inertia, a geometrical property that affects torsional behavior, was not significantly different between the Hyp femora and the same sex normals, differences in mechanical behavior were attributed to material properties.(ABSTRACT TRUNCATED AT 250 WORDS)
Task-specific and subject-specific lumbar trunk muscle function, muscle geometry, and vertebral density data were collected from 16 men. A biomechanical model was used to determine muscle strength and the compressive forces acting on the lumbar spine.
To develop an anatomic biomechanical model of the low back that could be used to derive task-specific muscle function parameters and to predict compressive forces acting on the low back. Several model-specific constraints were examined, including the notion of bilateral trunk muscle anatomic symmetry, the influence of muscle lines of action, and the use of density-derived vertebral strength for model validation.
Clinical and basic science investigators are currently using a battery of diverse biomechanical techniques to evaluate trunk muscle strength. Noteworthy is the large variability in muscle function parameters reported for different subjects and for different tasks. This information is used to calculate forces and moments acting on the low back, but limited data exist concerning the assessment of subject-specific, multiaxis, isometric trunk muscle functions.
A trunk dynamometer was used to measure maximum upright, isometric trunk moments in the sagittal (extension, flexion) and coronal (lateral flexion) planes. Task- and subject-specific trunk muscle strength or "gain" was determined from the measured trunk moments and magnetic resonance image-based muscle cross-sectional geometry. Model-predicted compressive forces obtained using muscle force and body force equilibrium equations were compared with density-derived estimates of compressive strength.
Individual task-specific muscle gain values differed significantly between subjects and between each of the tasks they performed (extension > flexion > lateral flexion). Significant differences were found between left side and right side muscle areas, and the lines of action of the muscles deviated significantly from the vertical plane. Model-predicted lumbar compressive forces were 38% (lateral flexion) to 73% (extension) lower that the L3 vertebral compressive strength estimated from vertebral density.
The present study suggests that biomechanical models of the low back should be based on task-specific and subject-specific muscle function and precise geometry. Vertebral strength estimates based upon vertebral density appear to be useful for validation of model force predictions.
Effects of fluoride on bone strength and cortical bone mass remain controversial. We compared 9-month, low-dose sodium fluoride (NaF) treatment with estrogen replacement therapy. Female Wistar rats 4.5 months old were divided into baseline, sham-operated (sham), sham-treated with NaF at 0.5 mg NaF/kg/day in drinking water, and ovariectomy (OVX), OVX treated with NaF and with estrogen. Bone mass was measured by dual X-ray absorptiometry (DXA) in vitro. Dimensions of the first lumbar vertebral body (L1) were determined by radiogrammetry. The right femur was processed undecalcified to obtain a midshaft cross-section to determine cross-sectional moments of inertia (CSMIs). L1 compressive test and left femoral torsional test were performed. OVX induced significant bone loss in L1 and femoral midshaft. Bone mass was increased to a greater extent in NaF-treated rats than in rats receiving estrogen replacement therapy. Femoral CSMIs in OVX rats, both L1 sizes and femoral CSMIs in NaF-treated rats, were significantly increased. Estrogen treatment had the least dimension expansion. OVX significantly decreased L1 compressive variables. There was no statistical difference in compressive parameters between NaF-treated groups and controls. OVX significantly increased femoral torsional strength but NaF treatment did not. Bone fluoride content was significantly increased after treatment with NaF. No significant difference in bone mineralization degree (ash and calcium) was found between treated and control rats. The discrepancy that an increase in bone mass and geometric properties in both trabecular and cortical bones by low-dose, long-term NaF treatment did not increase vertebral strength nor proportionally improve femoral strength indicated that the bone intrinsic biomechanical properties could be changed by NaF treatment.
It is difficult to determine when a growing organism has reached adult life and is fully developed. Closure of the epiphyseal growth plates has often been considered a sign of skeletal maturity, but these plates do not close in rats (1).
Thesis (Ph. D.)--University of Kentucky, 1970. Includes bibliographical references (leaves 130-138).
Structural development of bone in rats under earth gravity, simulated weightlessness, hypergravity, and mechanical vibration
In order to ascertain whether the intrinsic strength of human bone changes with age or not, we have determined the ultimate tensile strength and density of strips of femoral cortical bone. These femora were collected from cadavers varying in age from 13 to 97 years. The results show that both density and intrinsic strength of bone increase up to about the fourth decade of life and then decrease with age. However, the rate of decrease of strength is greater than that of density. This indicates that the density of bone is not the sole determining factor of its strength, and that some other factors play an important part.
Adult cortical and cancellous bone can be considered as a single material whose apparent density varies over a wide range. The compressive strength of bone tissue is proportional to the square of the apparent density. The compressive modulus is proportional to the cube of the apparent density. The strength and stiffness of bone approximately doubles as the rate of deformation is increased from a very slow to an extremely rapid rate. Strength and stiffness are proportional to the strain rate raised to the 0.06 power. Cortical bone is stronger in compression than tension. The shear strength for torsional loading about the long bone axis is less than the tensile strength. Secondary Haversian cortical bone is an anisotropic material which is transversely isotropic. It is stronger and stiffer in the longitudinal whole bone direction than in the transverse direction. Fracture as well as fatigue failure of bone is controlled more strongly by strain magnitude than stress magnitude. Bone fatigue caused by repeated mechanical loading is a gradual, progressive process which is accompanied by diffuse microscopic damage. Bone has poor fatigue resistance. Repeated loading of cortical bone at one-half the tensile yield strain produces fatigue failure in less than 10,000 loading cycles. Cortical bone morphology and composition can be characterized by an examination of microstructure, porosity, mineralization, and bone matrix. These parameters seldom vary independently but are usually observed to vary simultaneously. Mechanical properties vary through the cortical thickness due to variations in microstructure, porosity, and chemical composition. All normal adult cortical bone is lamellar bone. Most of the cortical thickness is composed of secondary Haversian bone. Circumferential lamellar bone is usually present at the endosteal and periosteal surfaces. In the adult, woven-fibered bone is formed only during rapid bone accretion, which accompanies conditions such as fracture callus formation, hyperparathyroidism, and Paget's disease. Mechanical properties are dependent on microstructure. The strongest bone type is circumferential lamellar bone, followed in descending order of strength by primary laminar, secondary Haversian, and woven-fibered bone. Osteons with longitudinally oriented collagen fibers are stronger in tension than osteons with transversely oriented fibers. Osteons with transversely oriented collagen fibers are stronger in compression than osteons with longitudinally oriented fibers. Mineralized tissue can be considered as a porous two-phase material consisting of collagen and mineral. An increase in collagen intermolecular cross-link density is associated with increased mineralization. The resulting tissue is stronger and stiffer as a result of increased mineral content and the stiffening of the collagen matrix. Defects in collagen metabolism can cause a decrease in mineralization, a loss of bone strength and stiffness, and an increase in ultimate strain to failure. Severe fluorosis increases cancellous bone strength but decreases cortical bone strength. Aging is associated with changes in bone microstructure which are caused primarily by internal remodeling throughout life. In the elderly, the bone tissue near the periosteal surface is stronger and stiffer than that near the endosteal surface due primarily to the porosity distribution through the cortical thickness caused by bone resorption. Bone collagen intermolecular cross-linking and mineralization increase markedly from birth to 17 years of age and continue to increase, gradually, throughout life. Adult cortical bone is stronger and stiffer and exhibits less deformation to failure than bone from children. Cortical bone strength and stiffness are greatest between 20 and 39 years of age. Further aging is associated with decrease in strength, stiffness, deformation to failure, and energy absorption capacity and an increase in plastic modulus.
The influence of maturation and senescence on the mechanical strength of bone was studied in rats by measuring the breaking load of the femur shaft and calculating the breaking strength. Strength of cartilage was studied by determining the ultimate load of femoral epiphyseal plate. A sharp increase of all mechanical parameters was found between the age of 1 and 4 months which was attributed to a maturation process. The maximum was achieved at 1 year followed by a decrease in all parameters. This was considered to reflect the aging or senescence process. The following biochemical parameters were determined in the same specimens: collagen and its soluble fractions, glycosaminoglycans, the fractions thereof, and elastin. The content of insoluble collagen was very closely correlated to the strength data, thus demonstrating an increase between 1 and 4 months, a plateau up to 1 year and a decrease at 2 years. During the maturation process, the glycosaminoglycans, especially the chondroitin sulfates, fell considerably. But also during the aging period, a further decrease was noted. The elastin content fell only slightly during the whole life span. The excellent correlation between strength parameters and content of insoluble collagen as found previously in skin could thus be confirmed. Strength of bone is apparently not dependent on the content of glycosaminoglycans and elastin. This indicates the major role of insoluble collagen for the mechanical properties of connective and supporting tissue. The studies presented here show that in rat bone the senescence process can be separated from the maturation process.Copyright © 1979 S. Karger AG, Basel
Ultimate compressive strength was studied at mid-length of the femur of female rats centrifuged from the age of 30 days at either 2.76 or 4.15 g for 810 days. The correlation between strength and age, cuberoot of body mass, femoral length, cross-sectional area/π, outer and inner radius at femoral mid-length and γ-ray absorption is significant and positive in the control animals ranging from 30 to 840 days. Except for the correlation between strength and photon absorption, the same correlations are negative or negligible in the 2.76 g group. Analysis of covariance reveals these correlation differences to be significant as regards femoral length and inner radius. The ultimate compressive strength of bone at the femoral mid-length is 10% greater in the animals centrifuged at 2.76 g, as compared to all control animals, if the mean values are adjusted with respect to body mass and outer radius, respectively.
The impact energy absorption of human femoral cortical bone decreases by a factor of about three between the ages of three and ninety. This decrease is associated with, and partially caused by, an increased mineralization of the bone. The porosity of the bone, which is highest at each end of the life span, is not dangerous in young bone but seems to exacerbate the effect of high mineralization in the old bone. Increased mineralization probably acts by decreasing the plastic deformation undergone before fracture starts. It may also make the process of crack travel less energetically expensive.
Bending measurements with fresh, wet femurs from 76 normal male white rats indicate material strength σu to increase with age t in proportion to the square L2 of bone-length. For conditions of constant t, however, σu is inversely proportional to L4. In studies where experimental treatment influences size, experimental values of σu should, therefore, be compared neither to those from rats of the same age and differing size, nor to those from the same size but differing age. Comparison relative to the value of the quantity σuL4 × 1055day ÷t is proposed. This comparison was demonstrated by determining whether smaller size alone could account for the greater σu of 26 rats reared during a week's centrifugation at 3 times normal gravity (3 g). The experimental σu was 40% greater than expected for control rats of comparable size and age.
A modular apparatus to measure the bending and torsional properties of the rat femur is presented. Both intact femur diaphyses and diaphyseal fractures in different phases of healing can be tested. It is also possible to measure the bending-strength of the distal femur metaphysis and the epiphyseal plate. the apparatus can be used to investigate the effect of drugs and hormones on the remodelling of the rat femur. © 1978 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.
Femoral fractures were created in rats to determine whether there were differences in healing under conditions of immobilization and under conditions of immediate weight-bearing. Histological and roentgenographic differences were present by the second week after fracture and differences in mechanical properties were also present. These differences became progressively greater during the next three weeks. Functional weight-bearing was found to accelerate the rate of fracture healing and to improve significantly the strength of the healing bone.
The influences of heterogeneity, anisotropy and geometric irregularity on the unrestrained, linearly elastic torsional response of long bones are assessed. Longitudinal geometric variations contribute insignificantly to the torsional response for typical long bone geometries. Anisotropy, heterogeneity and transverse geometric irregularity significantly influence the torsional response. A procedure is discussed which uses an approximate means to characterize both heterogeneity and anisotropy in predicting the torsional response. The accuracy of circular and elliptical annulus models of the bone cross-sectional geometry are assessed by comparing the stress predictions of these simple models to those of finite element models of the bone geometry.
Strain-controlled uniaxial fatigue and monotonic tensile tests were conducted on turned femoral cortical bone specimens obtained from baboons at various ages of maturity. Fatigue loading produced a progressive loss in stiffness and an increase in hysteresis prior to failure, indicating that immature primate cortical bone responds to repeated loading in a fashion similar to that previously observed for adult human cortical bone. Bone fatigue resistance under this strain controlled testing decreased during maturation. Maturation was also associated with an increase in bone dry density, ash fraction and elastic modulus. The higher elastic modulus of more mature bone meant that these specimens were subjected to higher stress levels during testing than more immature bone specimens. Anatomical regions along the femoral shaft exhibited differences in strength and fatigue resistance.
Biophysical properties of bone in the femur and tibia of the rat were measured during the life span of from 2–6 months during normal aging and exposure to 20 and 25 Hz mechanical vibration for 2 × 2·5 and 12 hr daily. Animals were successively sacrified at intervals of 20 and 60 days in order to determine the physical, mechanical and histological-physiological parameters of bone. Mineralization was traced by periodic administration of tetracycline. In normal aging the physical dimensions, density, rigidity, microhardness and ash content of bone increase. Bone porosity and total bone calcium content remain constant. Chronic vibration tends to increase stiffness and microhardness of bone. Modulus of elasticity and microhardness of vibrated bone are higher than those of non-vibrated bone. This is correlated to disorganization of mineral deposition: labeling by tetracycline shows that the regular zones of mineralization disappear under vibration and that mineral deposition becomes dispersed across the diaphysis. However, the ash and calcium contents of the femur are not affected by vibration. Bone porosity is also normal.
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.
The torsional behaviour of the femur has been studied in 145 male Wistar rats, aged 3-36 weeks. The ultimate torsional moment and the torsional stiffness of the femora increased with increasing animal age. In contrast, the femoral deformation at failure, the ultimate torsional angle, was almost constant for all age levels. The strength and stiffness of cortical bone as a material, the ultimate torsional stress and the modulus of rigidity reached a plateau when the rats were about 14 weeks old, and had a body weight and femoral length of about 350 g and 35 mm, respectively. In conclusion, cortical bone of Wistar rats probably reaches maturity at an age of about 14 weeks.
The age-related material properties of developing immature canine bone were determined for the femora, tibiae, humeri, radii, and ulnae in animals from 1 wk of age to maturity. These properties included bone geometry changes, material tissue properties, and qualitative and quantitative morphological evaluations. All bones exhibited a two-phase growth cycle, an initial rapid phase (20 wk) followed by a substantially slower growth to maturation (48 wk). All properties showed age-related changes except bone tissue strain to failure.
A strain gage based experimental method is presented which provides an alternative to use of area sectional properties for obtaining the cross sectional centroids, flexural rigidities and axial stiffness of whole bone specimens. While area sectional property computations require detailed records on the geometry of cross sections, the experimental method presented here requires only gage locations plus the applied loads and recorded strains. Both techniques are used to analyze the midshaft sectional properties of canine radii. The results demonstrate the advantage of the experimental method for the analysis of heterogeneous cross sections with an unknown distribution of bone elastic modulus. By applying the experimental and area methods together, effective elastic modulus values for the sections were obtained.
Mechanical properties of fractured and intact femora have been studied in young and adult, male rats. A standardized, closed, mid-diaphyseal fracture was produced in the left femur, the right femur serving as control. The fracture was left to heal without immobilization. At various intervals, both fractured and intact femora were loaded in torsion until failure. The fractured femora regained the mechanical properties of the contralateral, intact bones after about 4 weeks in young and after about 12 weeks in adult rats. For intact bones, both the ultimate torsional moment (strength) and the torsional stiffness increased with age of the animals, whereas the ultimate torsional angle remained unchanged. For bone as a material, however, the ultimate torsional stress (strength) and the modulus of rigidity (stiffness) increased with age only in young rats, being almost constant in the adult animals. The various biomechanical parameters of the healing fractures did not reach those of the contralateral, intact bones simultaneously. The torsional moment required to twist a healing femoral fracture 20 degrees (0.35 radians), a deformation close to what an intact femur can resist, proved to be a functional and simple measure of the degree of fracture repair in rats.
A technique for the fabrication of encapsulated micro-miniature rosette strain gages for in vivo implantation is described. The gage units have an overall area of ten square millimeters (2.5 mm X 4.0 mm), and hence can be installed in very small experimental animals, particularly rodents. Using a rat model, strain data for up to 12 days have been obtained and in vitro studies have validified the in vivo strain recordings.
Structural properties of growing canine long bones were determined from three and four-point bending tests. Mechanical and geometric properties were found to follow a biphasic growth process, with a rapid increase in bending strength and moment of inertia from l to 24 wk of age and a substantially decreased rate thereafter to maturity. Predicted bone tissue material properties were also found to follow this biphasic developmental process.
Mechanical properties of healing fractures and growing, intact bones were studied in male rats aged 8 weeks at the beginning of the study period. A standardized, closed fracture was produced in the middle of the left femur. The fracture was not immobilized. At various intervals after the fracture, the healing fractured femora and the contralateral, intact femora were subjected to bending, torsional and tensile tests. The fractured femora regained the strength and the ultimate deformation of the contralateral, intact femora after about 8 weeks when tested in bending, and after about 13 weeks when tested in torsion. In the first phases of fracture repair, the healing fractures could resist more torsional moments increased with increase in age and weight of the animals, whereas the ultimate angular deformation remained constant. The ultimate bending and torsional stresses (bone material strength) increased to reach a plateau when the rats were about 14 weeks old. No significant differences were observed between the bending, torsional and tensile application.
Formulas for Stress and Struin
- Roark Rj Young
- Wc
Roark RJ, Young WC: Formulas for Stress and Struin. New York, McGraw-Hill, Inc., 1975, p 292
Mechanical properties and com-position of cortical bone
- Carter Dr Spengler
- Dm
Carter DR, Spengler DM: Mechanical properties and com-position of cortical bone. Clin Orthop 135:192-217, 1978
- Ekeland
- Weir