Changes In Bone Material Properties Research Articles

Trabecular bone microcrack accumulation in patients treated with bisphosphonates for durations up to 16 years.

This study quantified the length, number, and density of microcracks in bone from patients treated with bisphosphonates as a function of duration. Anterior iliac crest bone samples from 51 osteoporotic Caucasian females continuously treated with oral bisphosphonates for 1-16 years were obtained by bone biopsy. Samples were histologically processed and analyzed for bone area, microcrack number, and microcrack length. The analyses used statistical modeling and considered patient age, bone mineral density, bone volume/total volume, trabecular thickness, and bone turnover as potential covariates. Microcrack density (number of microcracks/total examined bone area) was linearly related (p = 0.018) to bisphosphonate treatment duration. None of the analyzed covariates contributed significantly to the observed relationship between microcrack density and bisphosphonate treatment duration. Observed increases in microcrack density with increasing bisphosphonate treatment duration is important because increasing levels of microcracks may not only affect bone remodeling but also reduce elastic modulus and are suspected to adversely affect other mechanical properties that may influence fracture risk. The present findings add to our prior results showing changes in bone material properties and modulus with bisphosphonate treatment duration and thereby provide a more comprehensive assessment of the relationship between bisphosphonate treatment duration and bone quality. Statement of Clinical Significance: The present findings provide information guiding clinical use of oral bisphosphonates for post-menopausal osteoporosis therapy.

Influence of low dose naltrexone on Raman assisted bone quality, skeletal advanced glycation end-products and nano-mechanical properties in type 2 diabetic mice bone

Type 2 diabetes mellitus (T2DM) commonly affects the bone mineral phase and advanced glycation end-products (AGEs) which eventually led to changes in bone material properties on the nano and macro-scale. Several anti-diabetic compounds are widely used to control high blood sugar or glucose caused by T2DM. Low Dose Naltrexone (LDN), an opiate receptor antagonist, and a known TLR4 antagonist, treatment can improve glucose tolerance and insulin sensitivity in high-fat-diet (HFD) induced T2DM mice. However, the influences of LDN on the local bone quality, mineralization of the bone, and the skeletal AGEs levels have not been fully elucidated. The objective of this study is to understand the effect of LDN on Raman assisted bone quality, skeletal AGEs (determined by Raman spectroscopy), and nano-mechanical properties in HFD induced T2DM mice bone. In order to investigate these, mice and corresponding bones were divided into four groups (divided based on diet and treatment), (a) normal control diet treated with saline water, (b) normal control diet treated with LDN, (c) HFD treated with saline water, and (d) HFD treated with LDN. In T2DM condition (HFD treated with saline water), alteration of Raman-based compositional measures in bone quality including mineral-to-matrix ratios, carbonate substitution, mineral crystallinity, and collagen quality was observed. Our data also indicated that T2DM enhances the skeletal AGEs, and impairs the nano-mechanical properties. Interestingly, present results indicated that LDN controls the Raman-based compositional measures in bone quality in HFD induced T2DM mice bone. Additionally, LDN also protects the alteration of the skeletal AGEs levels and nano-mechanical properties in T2DM mice bone. This study concluded that LDN can control the HFD induced T2DM affected bone abnormalities at multiple hierarchical levels.

The effect of calcium and vitamin D supplementation on bone health of male Jockeys.

Engagement in high volumes of physical activity coupled with energy restriction during periods of musculoskeletal development may compromise bone health. Jockeys limit caloric intakes on a weekly basis often from their mid-to-late teens. The aim of this study was to establish whether calcium and vitamin D supplementation would improve bone turnover markers (BTM) and non-weight bearing bone properties of young male jockeys. A six-month randomised, double-blinded, placebo-controlled trial with two groups of apprentice male jockeys was conducted. Participants (age 20.18±3.23years) were supplemented with 800mg of calcium and 400IU of vitamin D (n=8) or a placebo (n=9) daily. Bone properties were assessed at the ultra-distal (4%) and proximal (66%) radius using pQCT at baseline and six months. Vitamin D, P1NP and CTX were assessed. ANCOVA results for blood-borne markers indicated higher vitamin D levels (18.1%, p=0.014, partial η2=0.38) and lower CTX (ng·L-1) (-24.8%, p=0.011, partial η2=0.40) in the supplemented group with no differences observed in P1NP. Analysis of bone variables indicated no between group differences in either trabecular or cortical bone properties at the 4% and 66% sites post-intervention. This trial is the first to examine the efficacy of calcium and vitamin D supplementation in improving non-weight bearing bone properties in a young male athletic population. Results indicate positive alterations to bone metabolism; however, longer duration or higher dosage appears to be required to detect changes in bone material properties at the radius. Further examination of such interventions in weight-restricted athletes is warranted.

Load-induced changes in bone stiffness and cancellous and cortical bone mass following tibial compression diminish with age in female mice

The vertebrate skeleton is an adaptive structure that responds to mechanical stimuli by increasing bone mass under increased mechanical loads. Although experimental animal models have shown the anabolic cortical bone response to applied load decreases with age, no consensus exists regarding whether this adaptive mechanism is affected by age in cancellous bone, the tissue most impacted by age-related bone loss. We used an established murine in vivo tibial loading model to characterize the load-induced cancellous, cortical and whole-bone responses to mechanical stimuli in growing and mature female mice at 6, 10 and 16 weeks of age. The effects of applied load on tibial morphology and stiffness were determined using microcomputed tomography and in vivo bone strains measured at the medial tibial midshaft during applied loading. At all ages, 2 weeks of applied load produced larger midshaft cortical cross-sectional properties (+13-72%) and greater cancellous bone volume (+21-107%) and thicker trabeculae (+31-68%) in the proximal metaphyses of the loaded tibiae. The relative anabolic response decreased from 6 to 16 weeks of age in both the cancellous and cortical envelopes. Load-induced tibial stresses decreased more in 6-week-old mice following loading, which corresponded to increased in vivo tibial stiffness. Stiffness in the loaded tibiae of 16-week-old mice decreased despite moderately increased cortical cross-sectional geometry, suggesting load-induced changes in bone material properties. This study shows that the cancellous and cortical anabolic responses to mechanical stimuli decline with age into adulthood and that cortical cross-sectional geometry alone does not necessarily predict whole-bone functional stiffness.

Glucocorticoid-induced osteoporosis : treatment update

Glucocorticoid-induced osteoporosis is one of the most important side effects of glucocorticoid use, as it leads to an increased risk of fracture. The skeletal effects of glucocorticoids include both direct and indirect actions on bone that result in an early, transient increase in bone resorption accompanied by a decrease in bone formation, which is maintained for the duration of glucocorticoid therapy. Rapid bone loss and increase fracture risk occur soon after the initiation of glucocorticoid therapy and dose dependent. The increase in fracture risk is partly independent of bone mineral density, probably as a result of changes in bone material properties and an increased risk of falling. Bisphosphonates are the front-line choice for prevention of fracture in glucocorticoid-treated patients, with teriparatide as the second-line option ; calcium and vitamin D supplements should be co-prescribed in the majority of individuals. Fracture risk can be assessed using the FRAX(®) algorithm, although risk may be underestimated in patients taking higher doses of glucocorticoids.

Age-specific profiles of tissue-level composition and mechanical properties in murine cortical bone

There is growing evidence that bone composition and tissue-level mechanical properties are significant determinants of skeletal integrity. In the current study, Raman spectroscopy and nanoindentation testing were co-localized to analyze tissue-level compositional and mechanical properties in skeletally mature young (4 or 5months) and old (19months) murine femora at similar spatial scales. Standard multivariate linear regression analysis revealed age-dependent patterns in the relationships between mechanical and compositional properties at the tissue scale. However, changes in bone material properties with age are often complex and nonlinear, and can be missed with linear regression and correlation-based methods. A retrospective data mining approach was implemented using non-linear multidimensional visualization and classification to identify spectroscopic and nanoindentation metrics that best discriminated bone specimens of different age-classes. The ability to classify the specimens into the correct age group increased by using combinations of Raman and nanoindentation variables (86–96% accuracy) as compared to using individual measures (59–79% accuracy). Metrics that best classified 4 or 5month and 19month specimens (2-age classes) were mineral to matrix ratio, crystallinity, modulus and plasticity index. Metrics that best distinguished between 4, 5 and 19month specimens (3-age classes) were mineral to matrix ratio, crystallinity, modulus, hardness, cross-linking, carbonate to phosphate ratio, creep displacement and creep viscosity. These findings attest to the complexity of mechanisms underlying bone tissue properties and draw attention to the importance of considering non-linear interactions between tissue-level composition and mechanics that may work together to influence material properties with age. The results demonstrate that a few non-linearly combined compositional and mechanical metrics provide better discriminatory information than a single metric or a single technique.

Clinical Question: What is the best approach to managing glucocorticoid-induced osteoporosis?

Glucocorticoid-induced osteoporosis is common, and the resulting fractures cause significant morbidity and mortality. Rapid bone loss and increased fracture risk occur soon after the initiation of glucocorticoid therapy and are dose dependent. The increase in fracture risk is partly independent of bone mineral density, probably as a result of changes in bone material properties and increased risk of falling. Fracture risk can be assessed using the FRAX algorithm, although risk may be underestimated in patients taking higher doses of glucocorticoids. Because of the rapidity of bone loss and increase in fracture risk after the start of glucocorticoid therapy, primary prevention should be advised in high-risk individuals, for example older women and men, individuals with a previous fracture history and those with low bone mineral density. Bisphosphonates are the front-line choice for the prevention of fracture in the majority of glucocorticoid-treated patients, with teriparatide as a second-line option. Calcium and vitamin D supplements should be co-prescribed unless there is evidence of an adequate dietary calcium intake and vitamin D status.

Management of glucocorticoid-induced osteoporosis

Glucocorticoid-induced osteoporosis is a common condition that results in significant morbidity and mortality. The skeletal effects of glucocorticoids include both direct and indirect actions on bone that result in an early, transient increase in bone resorption accompanied by a decrease in bone formation, which is maintained for the duration of glucocorticoid therapy. Rapid bone loss and increased fracture risk occur soon after the initiation of glucocorticoid therapy and are dose dependent. The increase in fracture risk is partly independent of bone mineral density, probably as a result of changes in bone material properties and an increased risk of falling. Bisphosphonates are the front-line choice for prevention of fracture in glucocorticoid-treated patients, with teriparatide as the second-line option; calcium and vitamin D supplements should be co-prescribed in the majority of individuals. Future guidelines for the management of glucocorticoid-induced osteoporosis should recognize the limitations of FRAX in assessing fracture risk in glucocorticoid-treated patients, and should include recently approved interventions, such as zoledronate and teriparatide.

Combination of Nanoindentation and Quantitative Backscattered Electron Imaging Revealed Altered Bone Material Properties Associated with Femoral Neck Fragility

Osteoporotic fragility fractures were hypothesized to be related to changes in bone material properties and not solely to reduction in bone mass. We studied cortical bone from the superior and inferior sectors of whole femoral neck sections from five female osteoporotic hip fracture cases (74–92 years) and five nonfractured controls (75–88 years). The typical calcium content (CaPeak) and the mineral particle thickness parameter (T) were mapped in large areas of the superior and inferior regions using quantitative backscattered electron imaging (qBEI) and scanning small-angle X-ray scattering, respectively. Additionally, indentation modulus (E) and hardness (H) (determined by nanoindentation) were compared at the local level to the mineral content (CaInd) at the indent positions (obtained from qBEI). CaPeak (−2.2%, P = 0.002), CaInd (−1.8%, P = 0.048), E (−5.6%, P = 0.040), and H (−6.0%, P = 0.016) were significantly lower for the superior compared to the inferior region. Interestingly, CaPeak as well as CaInd were also lower (−2.6%, P = 0.006, and –3.7%, P = 0.002, respectively) in fracture cases compared to controls, while E and H did not show any significant reduction. T values were in the normal range, independent of region (P = 0.181) or fracture status (P = 0.551). In conclusion, it appears that the observed femoral neck fragility is associated with a reduced mineral content, which was not accompanied by a reduction in stiffness and hardness of the bone material. This pilot study suggests that a stiffening process in the organic matrix component contributes to bone fragility independently of mineral content.

Glucocorticoid-Treated Mice Have Localized Changes in Trabecular Bone Material Properties and Osteocyte Lacunar Size That Are Not Observed in Placebo-Treated or Estrogen-Deficient Mice

This study compares changes in bone microstructure in 6-month-old male GC-treated and female ovariectomized mice to their respective controls. In addition to a reduction in trabecular bone volume, GC treatment reduced bone mineral and elastic modulus of bone adjacent to osteocytes that was not observed in control mice nor estrogen-deficient mice. These microstructural changes in combination with the macrostructural changes could amplify the bone fragility in this metabolic bone disease. Patients with glucocorticoid (GC)-induced secondary osteoporosis tend to fracture at higher bone mineral densities than patients with postmenopausal osteoporosis. This suggests that GCs may alter bone material properties in addition to BMD and bone macrostructure. Changes in trabecular bone structure, elastic modulus, and mineral to matrix ratio of the fifth lumbar vertebrae was assessed in prednisolone-treated mice and placebo-treated controls for comparison with estrogen-deficient mice and sham-operated controls. Compression testing of the third lumbar vertebrae was performed to assess whole bone strength. Significant reductions in trabecular bone volume and whole bone strength occurred in both prednisolone-treated and estrogen-deficient mice compared with controls after 21 days (p < 0.05). The average elastic modulus over the entire surface of each trabecula was similar in all the experimental groups. However, localized changes within the trabeculae in areas surrounding the osteocyte lacunae were observed only in the prednisolone-treated mice. The size of the osteocyte lacunae was increased, reduced elastic modulus around the lacunae was observed, and a "halo" of hypomineralized bone surrounding the lacunae was observed. This was associated with reduced (nearly 40%) mineral to matrix ratio determined by Raman microspectroscopy. These localized changes in elastic modulus and bone mineral to matrix ratio were not observed in the other three experimental groups. Based on these results, it seems that GCs may have direct effects on osteocytes, resulting in a modification of their microenvironment. These changes, including an enlargement of their lacunar space and the generation of a surrounding sphere of hypomineralized bone, seem to produce highly localized changes in bone material properties that may influence fracture risk.

Regional distinctions in cortical bone mineral density measured by pQCT can predict alterations in material property at the tibial diaphysis of the Cynomolgus monkey

We examined whether regional differences in cortical bone mineral density (Ct.BMD) measured by peripheral quantitative computed tomography is related to the heterogeneity of bone tissue and whether regional Ct.BMD is a better indicator of changes in bone material properties. Bilateral tibiae were obtained from 17 female adult Cynomolgus monkeys ( Macaca fascicularis; mean age 16.8 years). After determining that Ct.BMD was similar between the right and left tibiae, the left tibiae were used for bone histomorphometry and the right for a three-point bending test. The Ct.BMD in the posterior quadrant was significantly higher than that in the anterior quadrant. In the bone histomorphometric analysis, all parameters (i.e., average osteonal area, average osteonal bone area, osteon population density, percent osteonal area [%On.Ar], percent osteonal bone area [%On.B.Ar], percent osteonal area of initial remodeling [%Il.On.Ar], percent osteonal area of secondary remodeling [%Sd.On.Ar], porosity, and percent osteoid area in the posterior region) were significantly lower than those in the anterior region. The results indicated that in the same cross-section, bone tissue structure was heterogeneous. Both total- and posterior-Ct.BMD were positively correlated with breaking stress and negatively correlated with toughness, whereas anterior-Ct.BMD was positively correlated with elastic modulus. Backward stepwise multiple regression analyses indicated that posterior-Ct.BMD and total-Ct.BMD were the best variables for predicting breaking stress and toughness, respectively, when age is taken into account. The %On.Ar, %On.B.Ar, and %Il.On.Ar in the posterior region were negatively correlated with elastic modulus. The %On.Ar, %On.B.Ar, and %Sd.On.Ar in the posterior region were positively correlated with toughness. These findings indicated that regional Ct.BMD measurement is useful to assess changes in the material properties of bone associated with the degree of mineralization. In particular, anterior-, posterior-, and total-Ct.BMD can be used separately to predict changes in the material properties of the tibial diaphysis.

Non-Invasive Prediction of Fracture Risk Due to Benign and Metastatic Skeletal Defects

ABSTRACTThe skeleton is the third most common site of metastatic cancer and a third to half of all cancer cases metastasize to bone. While much has been learned about the mechanisms of metastatic spread of cancer to bone, little headway has been made in establishing reliable guidelines for estimating fracture risk associated with skeletal metastases.Our hypothesis is that a change in bone structural properties as a result of tumor-induced osteolysis determines the fracture risk in patients with skeletal metastases. Our goal was to develop an image based clinical tool to monitor the fracture risk associated with individual lesions in patients with skeletal metastases and to use this tool to optimize treatment and to monitor a patient's response to treatment. If bone is considered a rigid porous foam undergoing remodeling by osteoblasts and osteoclasts in response to local and/or systemic modulators of their activity, it follows that changes in bone material properties reflect the net effect of this remodeling activity. Therefore, image based methods that measure both bone mineral density and whole bone geometry can be used to monitor the response of skeletal metastases to anticancer treatment and to predict whether a specific lesion has weakened the bone sufficiently such that pathological fracture is imminent. In a series of laboratory experiments we demonstrated that the reduction in the load carrying capacity of a bone with simulated skeletal defects could be predicted accurately and non-invasively using computed tomography (CT). We also demonstrated that bone material properties from tissue excised from normal, osteoporotic and metastatic cancer bone specimens could be modeled analytically using a bivariate function of bone tissue density and bone volume fraction (Vvb). Since these bone specimens were inhomogeneous with respect to density distribution (as is the case for pathologic bonein-situ), the sub-region with the minimum-Vvbaccounted for more of the variability in the measured mechanical properties compared to the average Vvbfor the entire specimen. Therefore the “weakest” subregion governed most of the mechanical behavior of the pathologic bone specimens. We applied our methods for predicting fracture risk to analyze bones from children with benign bone defects and showed that our relatively simple methods were much better at predicting fracture (100% sensitive, 94% specific) than current radiographic based guidelines (66% accurate). Using CT based data to calculate the load bearing capacity of vertebrae infiltrated with metastatic breast carcinoma, we also predicted with 100% sensitivity and 69% specificity the occurrence of a new vertebral fracture in women with metastatic breast cancer. These results are in contrast to the best available fracture risk criteria based on the size and location of the lesion on CT images of the spine, which were only 22% specific. Our non-invasive, image based method that measures both bone mineral density and whole bone geometry may also be used to monitor the response of skeletal metastases to anticancer treatment and to predict whether a specific lesion has weakened the bone sufficiently such that pathological fracture is imminent.

Monophasic dose-response curves of betamethasone on geometric and mechanical properties of femur diaphyses in growing rats.

The biomechanical repercussion of the corticoid-induced osteopenia (a severe consequence of long-term glucocorticoid therapy) was studied in cortical bone of small rodents. Growing rats receiving 12.5-3200 micrograms/kg/d of betamethasone (BMS) s.c. for 20 days suffered a log-dose related impairment in body weight gain and in mechanical (fracture load, bending stiffness) and cross-sectional properties (area, moment of inertia) of femur diaphyses. No changes in bone material properties (ability to stand stress, elastic modulus, energy absorption per unit volume) were observed. At variance with the biphasic dose-response curves (positive effects at low-medium doses, negative at high doses) previously obtained with cortisol in a similar model, only negative effects on every variable studied were observed in this experiment. Results suggest that BMS effects on cortical bone biomechanics derived mainly or completely from those induced on bone geometry (biomechanical correlate of corticoid-induced osteopenia) in the assayed conditions. Data are compatible with a BMS-induced change in the setpoint of bone mechanostat. Correlation of bone geometric and biomechanical data with body weight gain showed that the anti-anabolic effects of BMS on bone were proportionally less intense than those exerted on the whole biomass.

Monophasic dose-response curves of betamethasone on geometric and mechanical properties of femur diaphyses in growing rats

The biomechanical repercussion of the corticoid-induced osteopenia (a severe consequence of long-term glucocorticoid therapy) was studied in cortical bone of small rodents. Growing rats receiving 12.5–3200 μg/kg/d of betamethasone (BMS) s.c. for 20 days suffered a log-dose related impairment in body weight gain and in mechanical (fracture load, bending stiffness) and cross-sectional properties (area, moment of inertia) of femur diaphyses. No changes in bone material properties (ability to stand stress, elastic modulus, energy absorption per unit volume) were observed. At variance with the biphasic dose-response curves (positive effects at low-medium doses, negative at high doses) previously obtained with cortisol in a similar model, only negative effects on every variable studied were observed in this experiment. Results suggest that BMS effects on cortical bone biomechanics derived mainly or completely from those induced on bone geometry (biomechanical correlate of corticoid-induced osteopenia) in the assayed conditions. Data are compatible with a BMS-induced change in the setpoint of bone mechanostat. Correlation of bone geometric and biomechanical data with body weight gain showed that the anti-anabolic effects of BMS on bone were proportionally less intense than those exerted on the whole biomass.