Femoral Biomechanical Properties Research Articles

Mice Lacking β-Adrenergic Receptors Have Increased Bone Mass but Are Not Protected from Deleterious Skeletal Effects of Ovariectomy

Activation of beta2-adrenergic receptors inhibits osteoblastic bone formation and enhances osteoclastic bone resorption. Whether beta-blockers inhibit ovariectomy-induced bone loss and decrease fracture risk remains controversial. To further explore the role of beta-adrenergic signaling in skeletal acquisition and response to estrogen deficiency, we evaluated mice lacking the three known beta-adrenergic receptors (beta-less). Body weight, percent fat, and bone mineral density were significantly higher in male beta-less than wild-type (WT) mice, more so with increasing age. Consistent with their greater fat mass, serum leptin was significantly higher in beta-less than WT mice. Mid-femoral cross-sectional area and cortical thickness were significantly higher in adult beta-less than WT mice, as were femoral biomechanical properties (+28 to +49%, P < 0.01). Young male beta-less had higher vertebral (1.3-fold) and distal femoral (3.5-fold) trabecular bone volume than WT (P < 0.001 for both) and lower osteoclast surface. With aging, these differences lessened, with histological evidence of increased osteoclast surface and decreased bone formation rate at the distal femur in beta-less vs. WT mice. Serum tartrate-resistance alkaline phosphatase-5B was elevated in beta-less compared with WT mice from 8-16 wk of age (P < 0.01). Ovariectomy inhibited bone mass gain and decreased trabecular bone volume/total volume similarly in beta-less and WT mice. Altogether, these data indicate that absence of beta-adrenergic signaling results in obesity and increased cortical bone mass in males but does not prevent deleterious effects of estrogen deficiency on trabecular bone microarchitecture. Our findings also suggest direct positive effects of weight and/or leptin on bone turnover and cortical bone structure, independent of adrenergic signaling.

Mineral density and biomechanical properties of bone tissue from male Arctic foxes ( Vulpes lagopus) exposed to organochlorine contaminants and emaciation

We investigated the impact from dietary OC (organochlorine) exposure and restricted feeding (emaciation) on bone mineral density (BMD; g hydroxy-apatite cm − 2 ) in femoral, vertebrate, skull and baculum osteoid tissue from farmed Arctic blue foxes ( Vulpes lagopus). For femur, also biomechanical properties during bending (displacement [mm], load [N], energy absorption [J] and stiffness [N/mm]) were measured. Sixteen foxes (EXP) were fed a wet food containing 7.7% OC-polluted minke whale ( Balaenoptera acutorostrata) blubber in two periods of body fat deposition (Aug–Dec) and two periods of body fat mobilisation (Jan–July) in which the food contained less energy and only 2% blubber. ΣOC food concentration in the food containing 7.7% whale blubber was 309 ng/g wet mass. This corresponded to a ΣOC exposure of ca. 17 µg/kg body mass/d and a responding ΣOC residue in subcutaneous adipose tissue of ca. 1700 ng/g live mass in the 8 EXP fat foxes euthanized after 16 months. A control group (CON) composed of 15 foxes were fed equal daily caloric amounts of clean pork ( Sus scrofa) fat. After 16 months, 8 EXP and 7 CON foxes were euthanized (mean body mass = 9.25 kg) while the remaining 8 EXP and 8 CON foxes were given restricted food rations for 6 months resulting in a body weight reduction (mean body mass = 5.46 kg). The results showed that only BMD skull vs. BMD vertebrae were significantly correlated ( R = 0.68; p = 0.03; n = 10) probably due to a similar composition of trabecular and cortical osteoid tissue. No difference in any of the BMD measurements or femoral biomechanical properties was found between EXP and CON foxes although BMD baculum was 1.6-folds lower in the EXP group. However, lean summer foxes had significantly lower femoral biomechanical properties measured as displacement (mm), energy absorption (J) and time (s) biomechanical properties than fat winter foxes (all p < 0.004). This indicates lower stiffness and softer bones from fasting which is in agreement with previous studies. Further, it should be kept in mind when studying bone tissues in Arctic mammals also in order to avoid confounding effects from body condition.

Bone biomechanical property deterioration due to tobacco smoke exposure.

Tobacco smoking has been implicated in the development of osteoporosis and early onset of menopause in women smokers. We measured various biomechanical properties of femurs and tibiae obtained from smoke-exposed and control mice to determine cigarette smoke influences on bone mass, structure, and strength. Growing female C57BL mice were exposed to sidestream cigarette smoke in a whole-body exposure chamber, set at 30 +/- 2 mg smoke particulates/m3 for 4 hours/day and 5 days/week for 12 consecutive weeks. Elevated levels of urinary cotinine and pulmonary ethoxyresorufin deethylase activity in smoke-exposed mice confirmed their effective exposure to cigarette smoke. There were no differences in body weight and physical size (length, medial-lateral and anterior-posterior widths, midshaft cortical area and thickness) of femurs and tibiae between smoke-exposed and control mice. The femoral mid-shaft yield load, stiffness, yield stress, and modulus were, respectively 8%, 13%, 10%, and 14% lower (P < 0.05) in smoke-exposed compared to control mice. The ultimate load and stress in mid-shaft femurs showed decreasing trends (P < 0.1) in smoke-exposed mice. In the femoral neck, the ultimate load and stiffness were 9% and 12% lower (P < 0.05) in smoke-exposed mice, respectively. Further, the ash-to-dry bone weight ratio was smaller ( approximately 6%, P < 0.05), and micro-computed tomographic scanning of distal femoral bone volume/total volume (%) and trabecular thickness showed decreasing trends in smoke-exposed mice compared to the control group. We conclude that exposure to tobacco smoke deteriorates some of the biomechanical properties of bone in growing female mice.

The influence of peripheral vascular disease on the carotid and femoral wall mechanics in subjects with abdominal aortic aneurysm.

Aortic and carotid stiffness is elevated in patients with abdominal aortic aneurysm (AAA). Peripheral vascular disease (PVD) frequently coexists with AAA and may further impair the arterial wall mechanics and increase the cardiovascular load. We therefore studied the elastic carotid and muscular femoral biomechanical properties and intima-media thickness (IMT) in this group of patients. The elastic indices and IMTs of the common carotid and common femoral arteries were determined in 30 patients with AAA (15 with PVD) with a duplex scanner coupled with a wall tracking system. Fasting plasma creatinine level, glucose and lipid concentrations, and their physiologic variables known to influence the arterial wall mechanics were also assessed. Patients with AAA and PVD have significantly stiffer carotid (Petersen's elastic modulus, 2207 +/- 905 mm Hg versus 1268 +/- 432 mm Hg; P =.001; stiffness index, 22.73 +/- 9.63 versus 12.60 +/- 4.24; P =.001] and femoral (Petersen's elastic modulus, 4906 +/- 4057 mm Hg versus 2599 +/- 1169 mm Hg; P =.043; stiffness index, 49.02 +/- 40.04 versus 26.07 +/- 13.22; P =.044) arteries than subjects with AAA alone. Although patients with PVD have thicker carotid and femoral IMTs, no statistical difference was seen between the two groups. The subjects were matched for age, body mass index, heart rate, systolic and diastolic blood pressures, total vascular risk score, plasma creatinine level, and fasting lipid and glucose concentrations. Subjects with PVD and AAA have significantly stiffer carotid and femoral arteries, which may indicate increased cardiovascular load and may account for the highest mortality rate seen in these patients in the UK Small Aneurysm Trial. Therefore, treatment of associated cardiovascular risk factors is important and may have to be tailored on an individual basis according to the findings of the arterial wall mechanics.

Vitamin K supplementation does not affect ovariectomy-induced bone loss in rats

Vitamin K may be important in bone metabolism. Notably, high-dose menaquinone-4 (menatetrenone, MK4) has been reported to reduce ovariectomy (ovx)-induced bone loss in rats and to decrease osteoporotic fracture in postmenopausal women. However, it is unclear whether these beneficial effects reflect a physiologic effect of vitamin K, or indicate direct pharmacologic activity of MK4. To further evaluate this, 60 6-month-old nulliparous Sprague-Dawley rats were randomized by distal femur bone mineral density (BMD) in a 3:1 ratio to ovx or sham groups. The sham and one ovx group’s diet contained 1% calcium and 1300 μg/kg of vitamin K1, phylloquinone. Diets of the other two ovx groups were supplemented with 882 mg phylloquinone or MK4 per kilogram chow. Distal femur bone mineral density (DFBMD) in an 8 mm region of interest was measured at baseline, 1 and 3 months postoperatively, utilizing dual-energy X-ray absorptiometry (DXA). All animals were killed at 3 months, their right femurs excised, ex vivo BMD measured by DXA, and biomechanical testing performed. No effect of phylloquinone or MK4 supplementation on ovx-induced bone loss was observed. Specifically, DFBMD declined 10.5%, 9.2%, and 11.2% at 1 month and 14.4%, 10.6%, and 13.9% at 3 months in the ovx control, high phylloquinone, and high MK4 groups, respectively. In addition, serum osteocalcin was elevated by ovx; this was not altered by phylloquinone or MK4. Finally, femoral biomechanical properties were not affected by phylloquinone or MK4. To conclude, in this study, neither high-dose phylloquinone nor MK4 reduced the ovx-associated increase in bone turnover or decline in DFBMD.

Variation in bone biomechanical properties, microstructure, and density in BXH recombinant inbred mice.

To test the hypothesis that factors associated with bone strength (i.e., volumetric bone mineral density [vBMD], geometry, and microstructure) have heritable components, we exploited the 12 BXH recombinant inbred (RI) strains of mice derived from C57BL/6J (B6; low bone mass) and C3H/HeJ (C3H; high bone mass) progenitor strains. The femurs and lumbar vertebrae from each BXH RI strain were characterized for phenotypes of vBMD, microstructural, biomechanical, and geometrical properties. Methods included bending (femur) and compression (vertebra) testing, peripheral quantitative computed tomography (pQCT), and microcomputed tomography (microCT). Segregation patterns of femoral and vertebral biomechanical properties among the BXH RI strains suggested polygenic regulation. Femoral biomechanical properties were strongly associated with femoral width in the anteroposterior (AP) direction and cortical thickness--geometric properties with complex genetic regulation. Vertebral vBMD and biomechanical properties measured in BXH RI strains showed a greater variability than either B6 or C3H progenitors, suggesting both progenitor strains have independent subsets of genes that yield similar vBMD and strength. The microCT and pQCT data suggested that the distribution of vertebral mineral into cortical and trabecular compartments is regulated genetically. Although the B6 and C3H progenitors had similar vertebral strength, their vertebral structures were markedly different: B6 had good trabecular bone structure and modest cortical bone mineral content (BMC), whereas C3H had high cortical BMC combined with a deficiency in trabecular structure. These structural traits segregated independently in the BXH RI strains. Finally, vertebral strength was not correlated consistently with femoral strength among the BXH RI strains, suggesting genetic regulation of bone strength is site specific.

Effects of exercise and disuse on bone remodeling, bone mass, and biomechanical competence in spontaneously diabetic female rats

Diabetes is associated with low bone formation. In this study we investigate the effect of additional or reduced mechanical loading on indices of bone formation and resorption, bone mass, and biomechanical properties in spontaneously diabetic BB rats. Female diabetic (mean age 13 weeks) and age-matched control rats were each allocated to three experimental groups: no-intervention; supervised running exercise program (Ex); and unloading induced by unilateral sciatic neurectomy (USN). The study period was 8 weeks. We measured biochemical parameters of bone formation (plasma osteocalcin) and resorption (urinary deoxypyridinoline [Dpd]); bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) at middiaphyseal and metaphyseal regions of the femur; histomorphometry of the proximal tibial metaphysis (PTM); and biomechanical properties of the femur (neck, diaphysis, and metaphysis) and lumbar vertebra (L-5). In nondiabetic rats, Ex did not affect parameters of bone formation/resorption and BMD, and had little effect on biomechanical properties. USN increased Dpd excretion, whereas there was a decreased trabecular bone formation rate (BFR) on morphometry of PTM in both paralyzed and intact limbs. Compared with intact limbs, paralyzed limbs of USN rats showed decreased trabecular bone volume at the PTM, and decreased BMD and biomechanical properties at the distal femoral metaphysis (DFM) and, to a lesser extent, femoral neck. Diabetic rats of the three experimental groups had low plasma osteocalcin levels and Dpd excretion, as well as low BFR on morphometry. The BMD and biomechanical properties of both femur and L-5 were unchanged in diabetic rats. Diabetic Ex rats, however, showed a lower maximum load and stress at DFM than control Ex rats. Diabetic USN rats showed no increase in Dpd excretion; their paralyzed limbs showed decreased maximum load at DFM, but there was no significant decrease in trabecular bone volume at PTM or BMD at DFM. Thus, the running exercise does not affect low bone formation in diabetic rats; however, trabecular bone loss caused by disuse is less pronounced in diabetic rats, probably as a result of low bone resorption.

The effects of dietary-induced obesity on the biomechanical properties of femora in male rats.

To assess the effects of diet-induced obesity (DIO), on the biomechanical and biochemical properties of the femur in mature male rats. Two groups of male rats were studied. The DIO experimental group was fed a high caloric diet and a 31% sucrose solution as drinking fluid for a month, whereas the control group was fed lab chow and tap water. Body weight; body water; lean body mass; femoral length; average cortical thickness; outer anteroposterior diameter; outer mediolateral diameter; cortex area; moment of inertia; cortical and cancellous bone hydration; tendon and muscle hydration; ash content of cortical and cancellous bone; ultimate load; deflection at ultimate load; ultimate strength; stiffness; elastic modulus and energy absorption capacity. 'Gainers' (final body weight in excess of three standard error of mean of the controls) were 19.1% heavier, with higher body fat, whereas body water, lean body mass, hydration of cancellous bone and ash content of cortical bone were lower, when compared to controls. Rats that failed to gain weight, despite the high caloric diet, were termed 'resisters' (weight gain less than three standard error of mean of the controls). Ultimate load, deflection at ultimate load and femoral energy absorption capacity were significantly higher in the experimental group when compared to the controls. However, no differences were found among the groups with respect to ultimate stress and stiffness. The weight gain produced by DIO may lead to bone adaptation and improved biomechanics.

A newly designed intramedullary fixation system for the femur-biomechanical properties and first clinical applications

A newly designed intramedullary fixation system for the femur-biomechanical properties and first clinical applications