Population-based study of age and sex differences in bone volumetric density, size, geometry, and structure at different skeletal sites

Whole bone geometry and bone quality in distal forearm fracture

Fracture of the distal radius is a sentinel for future increased risk of other "osteoporotic" fractures, in which the peak age for incidence of distal radius fracture is 5 to 10 years before that for spine and hip fractures. Mean bone mineral density (BMD) of the distal radius was lower in patients with osteoporosis compared with age- and sex-matched normal subjects. However, it has been shown that to predict the strength of the distal radius at the site where fractures occur requires more than measurement of bone mineral content (BMC) or BMD. Only moderate correlations have been found between forearm sites, which may be a result of differences in bone composition between sites. Different forearm sites may be used interchangeably for diagnostic purposes, but the prognostic value is not known. Using the distal radius as a screening tool for identifying individuals at risk of "osteoporotic" fracture shows that forearm site selection and accuracy of measurement can be important confounders in group studies.Improving resolution of computed tomography (CT) scanners has enabled quantitation of cortical bone density and cortical thickness. These measurements have enabled the mechanism of bone loss in the distal radius to be elucidated and show that, after menopause, bone loss is primarily through thinning of the cortex. CT imaging allows the precise localization of bone changes in individuals and should be of value in the assessment of the severity of osteoporosis. It also shows that this technology has the potential to determine the efficacy of therapeutic interventions. A concerted effort has been made to elucidate the interrelationships between the amount of bone and the geometry and that clinical imaging of BMC and/or cross-sectional area in the radius would provide improved prediction of an individual's risk of fracture.The technological tools are available, in the clinic, to accurately measure the 3-dimensional (3D) geometry of the distal radius and the amount of bone. In addition, the cortical and cancellous bone compartments can be analyzed separately. This capability, along with the easy accessibility of the distal radius to clinical imaging modalities, provides an excellent framework for longitudinal prospective studies to determine morphologic risk factors for osteoporotic fractures of the distal radius.

Advanced CT bone imaging in osteoporosis

Non-invasive and/or non-destructive techniques can provide structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, many studies indicate that BMD only partly explains bone strength. Quantitative assessment of macro- and microstructural features may improve our ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) DXA and CT, particularly volumetric quantitative CT (vQCT). Methods for assessing microstructure of trabecular bone non-invasively and/or non-destructively include high-resolution CT (hrCT), microCT (μCT), high-resolution magnetic resonance (hrMR) and microMR (μMR). vQCT, hrCT and hrMR are generally applicable in vivo; μCT and μMR are principally applicable in vitro. Despite recent progress made with these advanced imaging techniques, certain issues remain. The important balances between spatial resolution and sampling size, or between signal-to-noise and radiation dose or acquisition time, need further consideration, as do the complexity and expense of the methods vs their availability and accessibility. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry vs the more complex architectural features of bone or the deeper research requirements vs the broader clinical needs. The biological differences between the peripheral appendicular skeleton and the central axial skeleton must be further addressed. Finally, the relative merits of these sophisticated imaging techniques must be weighed with respect to their applications as diagnostic procedures, requiring high accuracy or reliability, compared with their monitoring applications, requiring high precision or reproducibility.

Structural basis of growth-related gain and age-related loss of bone strength

If bone strength was the only requirement of skeleton, it could be achieved with bulk, but bone must also be light. During growth, bone modelling and remodelling optimize strength, by depositing bone where it is needed, and minimize mass, by removing it from where it is not. The population variance in bone traits is established before puberty and the position of an individual's bone size and mass tracks in the percentile of origin. Larger cross-sections have a comparably larger marrow cavity, which results in a lower volumetric BMD (vBMD), thereby avoiding bulk. Excavation of a marrow cavity thus minimizes mass and shifts the cortex radially, increasing rigidity. Smaller cross-sections are assembled by excavating a smaller marrow cavity leaving a relatively thicker cortex producing a higher vBMD, avoiding the fragility of slenderness. Variation in cellular activity around the periosteal and endocortical envelopes fashions the diverse shapes of adjacent cross-sections. Advancing age is associated with a decline in periosteal bone formation, a decline in the volume of bone formed by each basic multicellular unit (BMU), continued resorption by each BMU, and high remodelling after menopause. Bone loss in young adulthood has modest structural and biomechanical consequences because the negative BMU balance is driven by reduced bone formation, remodelling is slow and periosteal apposition continues shifting the thinned cortex radially. But after the menopause, increased remodelling, worsening negative BMU balance and a decline in periosteal apposition accelerate cortical thinning and porosity, trabecular thinning and loss of connectivity. Interstitial bone, unexposed to surface remodelling becomes more densely mineralized, has few osteocytes and greater collagen cross-linking, and accumulates microdamage. These changes produce the material and structural abnormalities responsible for bone fragility.

A novel DXA-based hip failure index captures hip fragility independent of BMD

Capability of a novel dual-energy X-ray absorptiometry (DXA)-based hip failure index (HiFI) to discriminate between hip fracture cases and controls was evaluated. Given the constraints of planar DXA, the femoral neck was assumed a foam-filled ( approximately trabecular bone), thin-walled ( approximately cortical bone) sandwich structure, while HiFI estimated the critical force sufficient to buckle the wall of such a structure. Proximal femur DXA data from 1379 women aged 65yr and older, 268 with prior hip fracture were used. Comparison between standard areal bone mineral density (BMD), femur strength index (FSI), and HiFI was based on areas under receiver operatoring characteristic curves (AUC). The mean femoral neck BMD (SD) was 0.689 (0.109) g/cm(2) among the cases and 0.768 (0.119) g/cm(2) among the controls; the mean FSI 1.33 (0.36) and 1.54 (0.41), and the mean HiFI -0.28 (0.14) and -0.18 (0.15), respectively; all intergroup differences were highly significant (p<0.001). The intergroup difference for HiFI remained significant (p<0.002) after adjusting for age and BMD or FSI. The AUCs were 0.696 (95% confidence interval [CI]: 0.661-0.730) for BMD, 0.665 (0.630-0.700) for FSI, and 0.701 (0.666-0.736) for HiFI. In conclusion, HiFI may capture structural traits that account for femoral neck fragility independently of BMD or FSI. Obviously, the use of actual geometric and structural information from three-dimensional imaging of the femoral neck would help diminish the crude assumptions of the present DXA approach and reveal the true potential of the HiFI approach to gauge hip fragility and identify at-risk individuals for hip fractures.

Tibial bone geometry in chronic stroke patients: influence of sex, cardiovascular health, and muscle mass

This study aimed to examine the geometry of the tibia in chronic stroke survivors. Fifty-five ambulatory individuals with chronic stroke were included in the study. pQCT was used to obtain a cross-sectional scan of the tibia at the 30% site on both the paretic and nonparetic sides. Leg lean mass was derived from a total body scan using DXA. Each subject was also evaluated for peak oxygen consumption rate, spasticity, and functional mobility. Paired t-tests were used to compare the pQCT parameters between the two sides. Multiple linear regression analysis was used to identify the significant determinants of tibial bone strength index (BSI). In men, marrow cavity area on the paretic side was significantly greater than the nonparetic side (p = 0.011), whereas the total bone area showed no significant side-to-side difference (p = 0.252). In women, total bone area on the paretic side was significantly smaller than the nonparetic side (p = 0.003), whereas the marrow cavity area had no side-to-side difference (p = 0.367). Peak oxygen consumption (r(2) = 0.739, F(5,49) = 22.693, p < 0.001) and paretic leg lean mass (r(2) = 0.802, F(6,48) = 32.475, p < 0.001) remained independently associated with tibial BSI, after controlling for age, sex, body mass index, years since stroke onset, and physical activity level. The geometry of the tibia in stroke patients showed sex-specific side-to-side differences. The results suggested that, whereas endosteal resorption was apparent in men, periosteal resorption was more predominant in women. The results also highlight the potential importance of promoting cardiovascular health and leg muscle mass in enhancing bone geometry in chronic stroke survivors.

Hip axis length changes in 10,554 males and females and the association with femoral neck fracture

Hip axis length (HAL) has been proposed as an independent predictor of hip fracture risk in Caucasian females. There are, however, few data concerning its predictive risk in Chinese. The aim of this study was to investigate the changes of HAL in healthy Chinese population and the relationship between HAL and femoral neck fracture. The study population included 10,554 healthy Chinese people (8665 females, 1889 males) aged 20-97 yrs living in Shanghai. Cases were 106 patients (82 females, 24 males) aged 52 yrs old and over with femoral neck fracture. Controls were 106 age-matched healthy persons. All subjects were measured bone mineral density (BMD) at any site of proximal femur and HAL using dual-energy X-ray absorptiometry. HAL had significantly positive correlations with height and weight. After the adjustment of height and weight, HAL increased with age at 50 yrs of age and over in females, and no difference was found among the age groups in males. Males had longer HAL than females in all age groups. The peak BMD appeared in 30-44 yrs for females and 20-24 yrs for males and decreased thereafter, especially for females at 50 yrs old and over. HAL was similar in both fracture and control groups, whereas the BMD values at proximal femur were significantly lower in fracture group than in controls. There was no evidence that subjects with femoral neck fracture had longer HAL. Because of the limitations of retrospective study and relatively small fracture sample, prospective studies are required to determine the conclusions.

Osteoporosis in men

With the aging of the population, there is a growing recognition that osteoporosis and fractures in men are a significant public health problem, and both hip and vertebral fractures are associated with increased morbidity and mortality in men. Osteoporosis in men is a heterogeneous clinical entity: whereas most men experience bone loss with aging, some men develop osteoporosis at a relatively young age, often for unexplained reasons (idiopathic osteoporosis). Declining sex steroid levels and other hormonal changes likely contribute to age-related bone loss, as do impairments in osteoblast number and/or activity. Secondary causes of osteoporosis also play a significant role in pathogenesis. Although there is ongoing controversy regarding whether osteoporosis in men should be diagnosed based on female- or male-specific reference ranges (because some evidence indicates that the risk of fracture is similar in women and men for a given level of bone mineral density), a diagnosis of osteoporosis in men is generally made based on male-specific reference ranges. Treatment consists both of nonpharmacological (lifestyle factors, calcium and vitamin D supplementation) and pharmacological (most commonly bisphosphonates or PTH) approaches, with efficacy similar to that seen in women. Increasing awareness of osteoporosis in men among physicians and the lay public is critical for the prevention of fractures in our aging male population.

Inhibin and the regulation of bone mass

Inhibins A and B are gonadal peptide members of the transforming growth factor-beta superfamily that serve as negative feedback regulators of pituitary follicle-stimulating hormone (FSH). Accumulating evidence suggests that bone turnover and bone loss increase in women before menopause and the decrease in serum estradiol levels. Increased FSH levels have been correlated with some of these perimenopausal changes, whereas decreased inhibins strongly correlate with increases in bone formation and resorption across the menopause transition, and predict lumbar bone mass in perimenopausal women, likely resulting from the direct inhibin suppression of osteoblast and osteoclast development. Interestingly, continuous exposure of mice to inhibin A in vivo is anabolic and protective against gonadectomy-induced bone loss. Together, these data suggest inhibins contribute to the endocrine regulation of bone metabolism via a bimodal mechanism of action such that cycling inhibin exposure suppresses bone turnover, and continuous exposure to inhibins is anabolic.

Progressive subsidence of a tapered, proximally coated femoral stem in total hip arthroplasty

The purpose of this study was to determine if subsidence of a tapered, proximally porous- and hydroxyapatite-coated femoral implant with immediate postoperative weight-bearing differed between men and women. Modified Harris Hip Pain and Function Scores were collected preoperatively, and six weeks and one year postoperatively. Femoral subsidence was determined at six weeks and one year after surgery. Men demonstrated significantly increased Harris Hip Function Scores at six weeks, with slightly inferior Harris Hip Pain Scores at one year. Regardless of sex, subsidence was greater at one year than at six weeks; however, men subsided significantly more at one year than women (1.7 +/- 2.0 mm vs 1.0 +/- 1.4 mm, p = 0.03). While it appears that this stem provided excellent early fixation in women, it is unclear if the increased subsidence in men was more related to patient-related factors of age, weight and activity level or with specific implant characteristics.

Technology insight: noninvasive assessment of bone strength in osteoporosis

Fractures that result from osteoporosis are an enormous and growing concern for public health systems; as the population ages, the number of fractures worldwide will double or triple in the next 50 years. The ability of a bone to resist fracture depends not only on the amount of bone present, but also on the spatial distribution of the bone mass, the cortical and trabecular microarchitecture, and the intrinsic properties of the materials that comprise the bone. Although low bone mineral density is one of the strongest risk factors for fracture, a number of clinical studies have demonstrated the limitations of using measurements of areal bone mineral density by dual-energy X-ray absorptiometry to assess fracture risk and to monitor responses to therapy. As a result, new, noninvasive imaging techniques that are capable of assessing various components of bone strength are being developed. These techniques include three-dimensional assessments of bone density, geometry and microarchitecture, as well as integrated measurements of bone strength by engineering analyses. Although they show strong potential, further development and validation of these techniques is needed to define their role in the clinical management of individuals with osteoporosis.

Does thoracic or lumbar spine bone architecture predict vertebral failure strength more accurately than density?

Trabecular bone microstructure was studied in 6 mm bone biopsies taken from the 10th thoracic and 2nd lumbar vertebra of 165 human donors and shown to not differ significantly between these sites. Microstructural parameters at the locations examined provided only marginal additional information to quantitative computed tomography in predicting experimental failure strength.

INTRODUCTION

It is unknown whether trabecular microstructure differs between thoracic and lumbar vertebrae and whether it adds significant information in predicting the mechanical strength of vertebrae in combination with QCT-based bone density.

METHODS

Six mm cylindrical biopsies taken at mid-vertebral level, anterior to the center of the thoracic vertebra (T) 10 and the lumbar vertebra (L) 2 were studied with micro-computed tomography (microCT) in 165 donors (age 52 to 99 years). The segment T11-L1 was examined with QCT and tested to failure using a testing machine.

RESULTS

The correlation of microstructural properties was moderate between T10 and L2 (r <or= 0.5). No significant differences were observed in the microstructural properties between the thoracic and lumbar spine, nor were sex differences at T10 or L2 observed. Cortical/subcortical density of T12 (r(2)=48%) was more strongly correlated with vertebral failure stress than trabecular density (r(2)=32%). BV/TV (of T10) improved the prediction by 52% (adjusted r(2)) in a multiple regression model.

CONCLUSION

Microstructural properties of trabecular bone biopsies displayed a high degree of heterogeneity between vertebrae but did not differ significantly between the thoracic and lumbar spine. At the locations examined, bone microstructure only marginally improved the prediction of structural vertebral strength beyond QCT-based bone density.

Peripheral quantitative computed tomography of the tibia: pediatric reference values

Peripheral quantitative computed tomography (pQCT) has been used in a number of pediatric studies. Reference data for children are primarily limited to the radius. The purpose of this study was to establish normal reference ranges for pQCT measurements of the tibia for children. A cross-sectional sample of healthy, white, non-Hispanic children aged 5-18 years (n=416; 197 boys) was measured at the distal tibia metaphysis and diaphysis by pQCT to assess trabecular and cortical bone, respectively. Differences were determined between and within genders by height for bone geometry, density, and strength. Height-specific normal ranges were calculated, and gender-specific centile curves were generated. A positive, linear relationship was found between tibia cortical bone geometry and strength parameters and height (r2 >or=0.58, p<0.001), with mean values greater for boys than girls (p <or=0.05). Trabecular volumetric bone mineral density values were relatively stable, but greater in boys than girls independent of height or age (p <or=0.01). The reference data for pQCT analyses of the tibia provide additional information on bone size, geometry, and strength in children. pQCT technology provides an additional tool for the evaluation of bone health in young subjects.

Longitudinal changes in BMD and bone geometry in a population-based study

We prospectively examined vBMD and structural bone parameters assessed by QCT among participants of the InCHIANTI study over a 6-yr follow-up. Periosteal apposition occurred both in men and women. Endocortical resorption causes bone loss in older women despite periosteal apposition.

INTRODUCTION

To address the hypothesis that age-related changes in BMD and bone geometry may be different in men and women, we prospectively examined volumetric BMD (vBMD) and structural bone parameters assessed by QCT among participants of the InCHIANTI study over a 6-yr follow-up.

MATERIALS AND METHODS

Three hundred forty-five men and 464 women 21-102 yr of age from the InCHIANTI study, a population-based study in Tuscany, Italy, were included. Tibial QCT bone parameters were measured at enrollment (1998-2000) and at 3- (2001-2003) and 6-yr (2004-2006) follow-ups.

RESULTS

Periosteal apposition occurred both in men and women. The annual rate of bone periosteal apposition was higher in younger than in older men, whereas in women, the rate of apposition was homogenous across age groups. The age-related medullary expansion, expression of endocortical resorption, was significantly higher in women compared with men. In women, but not in men, accelerated endocortical resorption not sufficiently balanced by periosteal apposition caused accelerated loss in cortical bone mass. The cross-sectional moment of inertia decreased progressively over the life span in both sexes.

CONCLUSIONS

Endocortical resorption causes bone loss in older women despite periosteal apposition. Obtaining a balance between endocortical resorption and periosteal apposition should be the target for interventions aimed to decrease bone loss and prevent osteoporosis in older women.

Bone degeneration and recovery after early and late bisphosphonate treatment of ovariectomized wistar rats assessed by in vivo micro-computed tomography

Bisphosphonates are antiresorptive drugs commonly used to treat osteoporosis. It is not clear, however, what the influence of the time point of treatment is. Recently developed in vivo micro-computed tomographic (CT) scanners offer the possibility to study such effects on bone microstructure in rats. The aim of this study was to determine the influence of early and late zoledronic acid treatment on bone in ovariectomized rats, using in vivo micro-CT. Twenty-nine female Wistar rats were divided into the following groups: ovariectomy (OVX, n = 5), OVX and zoledronic acid (ZOL) at week 0 (n = 8), OVX and ZOL at week 8 (n = 7), and sham (n = 9). CT scans were made of the proximal tibia at weeks 0, 2, 4, 8, 12, and 16; and bone structural parameters were determined in the metaphysis. Two fluorescent labels were administered to calculate dynamic histomorphometric parameters. At week 16, all groups were significantly different from each other in bone volume fraction (BV/TV), connectivity density, and trabecular number (Tb.N), except for the early ZOL and control groups which were not significantly different for any structural parameter. After ZOL treatment at week 8, BV/TV, structure model index, Tb.N, and trabecular thickness significantly improved in the late ZOL group. The OVX and ZOL groups showed, respectively, higher and lower bone formation rates than the control group. Early ZOL treatment inhibited all bone microstructural changes seen after OVX. Late ZOL treatment significantly improved bone microstructure, although the structure did not recover to original levels. Early ZOL treatment resulted in a significantly better microstructure than late treatment. However, late treatment was still significantly better than no treatment.

Glucocorticoid excess affects cortical bone geometry in premenopausal, but not postmenopausal, women

Glucocorticoid (GC) excess causes a great increase in fracture risk, but the effects of GC excess on cortical bone geometry are unknown. The present study was performed to examine the effects of GC excess on cortical bone geometry in both premenopausal and postmenopausal women. Ninety-six women receiving oral GC treatments and 10 women with Cushing syndrome (CS) were each compared to age-matched control subjects using peripheral quantitative computed tomography. Total area, periosteal circumference, and polar strength strain index (SSIp) were significantly lower in GC-treated patients compared with control subjects in premenopausal women but not in postmenopausal women. Moreover, cortical area and thickness as well as periosteal circumference and SSIp were significantly lower in patients with CS compared to controls in premenopausal women but not in postmenopausal women. Total area, cortical area, cortical thickness, periosteal circumference, as well as SSIp were significantly lower in GC-treated patients with vertebral fractures compared to those without vertebral fractures in premenopausal women but not in postmenopausal women. In conclusion, endogenous or exogenous GC excess affects bone geometry of forearms of premenopausal, but not postmenopausal, women. These effects of GC excess on bone geometry may provide a strength loss mechanism beneath increased vertebral fracture risk.

A population-based assessment of rates of bone loss at multiple skeletal sites: evidence for substantial trabecular bone loss in young adult women and men

Using QCT, we made a longitudinal, population-based assessment of rates of bone loss over life at the distal radius, distal tibia, and lumbar spine. Cortical bone loss began in perimenopause in women and later in life in men. In contrast, trabecular bone loss began in young adulthood in both sexes.

INTRODUCTION

Although conventional wisdom holds that bone loss begins at menopause in women and later in life in men, this has not been examined longitudinally in population-based studies using precise technology capable of distinguishing cortical and trabecular bone.

MATERIALS AND METHODS

In an age- and sex-stratified population sample (n = 553), we measured volumetric BMD (vBMD) of trabecular and cortical bone by QCT annually for up to 3 yr at the distal radius (DR) and distal tibia (DT) (n = 552) and trabecular vBMD at baseline and 3 yr at the lumbar spine (LS) (n = 474).

RESULTS

Substantial cortical bone loss began in middle life in women but began mainly after age 75 in men. In contrast, substantial trabecular bone loss began in young adult women and men at all three skeletal sites and continued throughout life with acceleration during perimenopause in women. Women experienced 37% and men experienced 42% of their total lifetime trabecular bone loss before age 50 compared with 6% and 15%, respectively, for cortical bone. Median rates of change in trabecular bone (%/yr) were -0.40, -0.24, and -1.61 in young adult women and -0.38, -0.40, and -0.84 in young adult men at the DR, DT, and LS, respectively (all p < 0.001). The early trabecular bone loss did not consistently correlate with putative causal factors, except for a trend with IGF-related variables at DT in women. However, in postmenopausal women and, to a lesser extent, in older men, higher rates of cortical and trabecular bone loss were associated with lower levels of biologically-active sex steroids and with higher levels of follicle-stimulating hormone and bone turnover markers.

CONCLUSIONS

The late onset of cortical bone loss is temporally associated with sex steroid deficiency. However, the early-onset, substantial trabecular bone loss in both sexes during sex steroid sufficiency is unexplained and indicates that current paradigms on the pathogenesis of osteoporosis are incomplete.

In vivo 3D reconstruction of human vertebrae with the three-dimensional X-ray absorptiometry (3D-XA) method

We used a standard DXA device equipped with a C-arm to do in vivo reconstruction of human vertebrae from two orthogonal scans. This new technique, called 3D-XA (three-dimensional X-ray absorptiometry), allows the direct measurement of geometric parameters of the vertebrae with a good accuracy and precision.

INTRODUCTION

Geometric parameters are predictors of bone strength. A technique called three-dimensional X-ray absorptiometry (3D-XA) allows 3D reconstruction of bones from DXA scans. We used the 3D-XA method to reconstruct human vertebrae and to evaluate the method's in vitro accuracy and in vivo precision.

METHODS

A standard DXA device equipped with a C-arm was used. Calibration of its environment and identification of different anatomical landmarks of the vertebrae allows personalized 3D geometric reconstruction of vertebrae. Accuracy was calculated by reconstructing 16 dry human vertebrae by 3D-XA and CT scanner. In vivo inter-observer precision was calculated using 20 human spines.

RESULTS

The mean difference between 3D reconstruction by CT and 3D-XA was -0.2 +/- 1.3 mm. The in vivo mean difference of the 3D-XA method between the two rheumatologists was -0.1 +/- 0.8 mm. For geometric parameters, mean difference ranged from 0.4 to 0.9 mm. For cross-sectional area and vertebral body volume, it was 2.9% and 3.2%, respectively.

CONCLUSION

This study shows the good accuracy and precision of 3D-XA using a standard DXA device. It yields complementary information on bone geometry. Further studies are needed to evaluate if, coupled with bone density, it improves vertebral fracture risk prediction.

Prevalence of osteoporosis and reference data for lumbar spine and hip bone mineral density in a Korean population

The aims of this study were to establish reference data for bone mineral density (BMD) at central skeletal sites using Lunar dual-energy X-ray absorptiometry (DXA), and to estimate the age-and sex-specific prevalence of osteoporosis in a Korean population. We performed a population-based, cross-sectional study. The subjects were 4148 (1810 men and 2338 women) Korean adults, aged 20-79 years. The BMD for central sites (lumbar spine, femoral neck, trochanter, and Ward's triangle) were measured by DXA. The standardized prevalence of osteoporosis among individual aged 50-79 years in lumbar spine, femoral neck, Ward's triangle, and trochanter was 40.1%, 12.4%, 28.4%, and 4.4% in women and 6.5%, 5.9%, 3.7%, and 1.6% in men, respectively. In women, peak BMD occurred in the age range 40-49 years for the femoral neck and trochanter, 30-39 years for the lumbar spine, and 20-29 years for Ward's triangle. In men, peak BMD values were observed at 20-29 years for all measured sites. This study establishes a normative database for BMD at central skeletal sites using dual-energy X-ray absorptiometry and provides more reliable information on the prevalence of osteoporosis in Korea.

Osteoclast precursors display dynamic metabolic shifts toward accelerated glucose metabolism at an early stage of RANKL-stimulated osteoclast differentiation

Mature osteoclasts have an increased citric acid cycle and mitochondrial respiration to generate high ATP production and ultimately lead to bone resorption. However, changes in metabolic pathways during osteoclast differentiation have not been fully illustrated. We report that glycolysis and oxidative phosphorylation characterized by glucose and oxygen consumption as well as lactate production were increased during receptor activator of nuclear factor-kappaB ligand (RANKL)-induced osteoclastogenesis from RAW264.7 and bone marrow-derived macrophage cells. Cell proliferation and differentiation varied according to glucose concentrations (0 to 100 mM). Maximal cell growth occurred at 20 mM glucose concentration and differentiation occurred at 5 mM concentration. Despite the similar growth rates exhibited when cultured cells were exposed to either 5 mM or 40 mM glucose, their differentiation was markedly decreased in high glucose concentrations. This finding suggests the possibility that osteoclastogenesis could be regulated by changes in metabolic substrate concentrations. To further address the effect of metabolic shift on osteoclastogenesis, we exposed cultured cells to pyruvate, which is capable of promoting mitochondrial respiration. Treatment of pyruvate synergistically increased osteoclastogenesis through the activation of RANKL-stimulated signals (ERK and JNK). We also found that osteoclastogenesis was retarded by blocking ATP production with either the inhibitors of mitochondrial complexes, such as rotenone and antimycin A, or the inhibitor of ATP synthase, oligomycin. Taken together, these results indicate that glucose metabolism during osteoclast differentiation is accelerated and that a metabolic shift towards mitochondrial respiration allows high ATP production and induces enhanced osteoclast differentiation.

Structural determinants of vertebral fracture risk

Vertebral fractures are more strongly associated with specific bone density, structure, and strength parameters than with areal BMD, but all of these variables are correlated.

INTRODUCTION

It is unclear whether the association of areal BMD (aBMD) with vertebral fracture risk depends on bone density per se, bone macro- or microstructure, overall bone strength, or spine load/bone strength ratios.

MATERIALS AND METHODS

From an age-stratified sample of Rochester, MN, women, we identified 40 with a clinically diagnosed vertebral fracture (confirmed semiquantitatively) caused by moderate trauma (cases; mean age, 78.6 +/- 9.0 yr) and compared them with 40 controls with no osteoporotic fracture (mean age, 70.9 +/- 6.8 yr). Lumbar spine volumetric BMD (vBMD) and geometry were assessed by central QCT, whereas microstructure was evaluated by high-resolution pQCT at the ultradistal radius. Vertebral failure load ( approximately strength) was estimated from voxel-based finite element models, and the factor-of-risk (phi) was determined as the ratio of applied spine loads to failure load.

RESULTS

Spine loading (axial compressive force on L3) was similar in vertebral fracture cases and controls (e.g., for 90 degrees forward flexion, 2639 versus 2706 N; age-adjusted p = 0.173). However, fracture cases had inferior values for most bone density and structure variables. Bone strength measures were also reduced, and the factor-of-risk (phi) was 35-37% greater (worse) among women with a vertebral fracture. By age-adjusted logistic regression, relative risks for the strongest fracture predictor in each of the five main variable categories were bone density (total lumbar spine vBMD: OR per SD change, 2.2; 95% CI, 1.1-4.3), bone geometry (vertebral apparent cortical thickness: OR, 2.1; 95% CI, 1.1-4.1), bone microstructure (none significant); bone strength ("cortical" [outer 2 mm] compressive strength: OR, 2.5; 95% CI, 1.3-4.8), and factor-of-risk (phi for 90 degrees forward flexion/overall vertebral compressive strength: OR, 3.2; 95% CI, 1.4-7.5). These variables were correlated with spine aBMD (partial r, -0.32 to 0.75), but each was a stronger predictor of fracture in the logistic regression analyses.

CONCLUSIONS

The association of aBMD with vertebral fracture risk is explained by its correlation with more specific bone density, structure, and strength parameters. These may allow deeper insights into fracture pathogenesis.

Femoral neck BMD is a strong predictor of hip fracture susceptibility in elderly men and women because it detects cortical bone instability: the Rotterdam Study

We studied HSA measurements in relation to hip fracture risk in 4,806 individuals (2,740 women). Hip fractures (n = 147) occurred at the same absolute levels of bone instability in both sexes. Cortical instability (propensity of thinner cortices in wide diameters to buckle) explains why hip fracture risk at different BMD levels is the same across sexes.

INTRODUCTION

Despite the sexual dimorphism of bone, hip fracture risk is very similar in men and women at the same absolute BMD. We aimed to elucidate the main structural properties of bone that underlie the measured BMD and that ultimately determines the risk of hip fracture in elderly men and women.

MATERIALS AND METHODS

This study is part of the Rotterdam Study (a large prospective population-based cohort) and included 147 incident hip fracture cases in 4,806 participants with DXA-derived hip structural analysis (mean follow-up, 8.6 yr). Indices compared in relation to fracture included neck width, cortical thickness, section modulus (an index of bending strength), and buckling ratio (an index of cortical bone instability). We used a mathematical model to calculate the hip fracture distribution by femoral neck BMD, BMC, bone area, and hip structure analysis (HSA) parameters (cortical thickness, section modulus narrow neck width, and buckling ratio) and compared it with prospective data from the Rotterdam Study.

RESULTS

In the prospective data, hip fracture cases in both sexes had lower BMD, thinner cortices, greater bone width, lower strength, and higher instability at baseline. In fractured individuals, men had an average BMD that was 0.09 g/cm(2) higher than women (p < 0.00001), whereas no significant difference in buckling ratios was seen. Modeled fracture distribution by BMD and buckling ratio levels were in concordance to the prospective data and showed that hip fractures seem to occur at the same absolute levels of bone instability (buckling ratio) in both men and women. No significant differences were observed between the areas under the ROC curves of BMD (0.8146 in women and 0.8048 in men) and the buckling ratio (0.8161 in women and 0.7759 in men).

CONCLUSIONS

The buckling ratio (an index of bone instability) portrays in both sexes the critical balance between cortical thickness and bone width. Our findings suggest that extreme thinning of cortices in expanded bones plays a key role on local susceptibility to fracture. Even though the buckling ratio does not offer additional predictive value, these findings improve our understanding of why low BMD is a good predictor of fragility fractures.

Age-related decline in trabecular and cortical density: a 5-year peripheral quantitative computed tomography follow-up study of pre- and postmenopausal women

This 5-year prospective study assessed changes in trabecular and cortical volumetric bone density at the non-weight-bearing radius and weight-bearing tibia among clinically healthy pre- and postmenopausal women. Altogether 79 premenopausal (mean age +/- SD at baseline 33 +/- 2 years) and 108 postmenopausal (68 +/- 2 years) women participated in the baseline and follow-up measurements. Trabecular density (TrD) of the distal radius and tibia and cortical density (CoD) of the radial and tibial shafts were assessed by peripheral quantitative computed tomography (pQCT). Repeated measures analysis of variance was used to analyze differences of means and mean changes between the age groups. As expected, TrD and CoD values were greater among premenopausal than postmenopausal women. Changes in radial TrD were similar in both age groups: mean (95% confidence interval) TrD of the distal radius declined by 3.0 mg/cm(3) (-0.9 to 7.0) and 5.1 mg/cm(3) (1.8-8.5) in the younger and older age groups, respectively. The respective declines in TrD of the distal tibia were 4.1 mg/cm(3) (2.1-6.0) and 2.8 mg/cm(3) (1.2-4.3). Decline in CoD was greater in the older than younger age group at both the radial and tibial shafts (P < 0.001). The mean absolute declines in radial CoD were 33.3 mg/cm(3) (27.9-38.7) and 49.4 mg/cm(3) (44.9-53.9) in younger and older women, and the declines in tibial CoD were 16.5 mg/cm(3) (12.6-20.2) and 28.1 mg/cm(3) (25.0-31.2), respectively. In conclusion, volumetric TrD in the weight-bearing tibia and non-weight-bearing radius showed similar age-related declines among pre- and postmenopausal women, while the decline in CoD was greater among postmenopausal women.

Contribution of in vivo structural measurements and load/strength ratios to the determination of forearm fracture risk in postmenopausal women

Bone structure, strength and load-strength ratios contribute to forearm fracture risk independently of areal BMD.

INTRODUCTION

Technological and conceptual advances provide new opportunities for evaluating the contribution of bone density, structure, and strength to the pathogenesis of distal forearm fractures.

MATERIALS AND METHODS

From an age-sratified random sample of Rochester, MN, women, we compared 18 with a distal forearm fracture (cases) to 18 age-matched women with no osteoporotic fracture (controls). High-resolution pQCT was used to assess volumetric BMD (vBMD), geometry, and microstructure at the ultradistal radius, the site of Colles' fractures. Failure loads in the radius were estimated from microfinite element (microFE) models derived from pQCT. Differences between case and control women were assessed, and the risk of fracture associated with each variable was estimated by logistic regression analysis.

RESULTS

Given similar heights, estimated loading in a fall on the outstretched arm was the same in cases and control. However, women with forearm fractures had inferior vBMD, geometry, microstructure, and estimated bone strength. Relative risks for the strongest determinant of fracture in each of the five main variable categories were as follows: BMD (total vBMD: OR per SD change, 4.2; 95% CI, 1.4-12), geometry (cortical thickness: OR, 4.0; 95% CI, 1.4-11), microstructure (trabecular number: OR, 2.3; 95% CI, 1.02-5.1), and strength (axial rigidity: OR, 3.8; 95% CI, 1.4-10); the factor-of-risk (fall load/microFE failure load) was 24 % greater (worse) in cases (OR, 3.0; 95% CI, 1.2-7.5). Areas under ROC curves ranged from 0.72 to 0.82 for these parameters.

CONCLUSIONS

Bone geometry, microstructure, and strength contribute to forearm fractures, as does BMD, and these additional determinants of risk promise greater insights into fracture pathogenesis.

Biomechanics of osteoporotic fractures

The objective of this review article is to present biomechanics concepts and data relevant to osteoporotic fractures. Fractures are mechanical events that occur when the applied load exceeds the fracture load (bone strength); both loading and strength must be considered to understand fracture risk. Hip fractures are almost always due to a fall, but only 5% of falls result in fracture. Hip fracture risk is greatest for a sideways fall that impacts on the greater trochanter. The loading events that cause vertebral fractures are poorly understood but include falls and heavy lifting. Activities that involve forward flexion and lifting generate the largest forces on the spine. Factors that affect bone strength include bone size (geometry) and bone density (vBMD). Men have larger bones at all ages compared to women and this is the main factor in the gender difference in whole-bone strength. Both men and women lose trabecular bone density and thus bone strength with aging, which is the main reason for the age-related loss of bone strength at the hip and spine, although dramatic decreases in the toughness of cortical bone may also contribute to osteoporotic fragility. The factor of risk (applied force/fracture force) is a useful concept for considering both the injury and the disease component of osteoporotic fractures. Within this article, I will review data on age-related changes in factors that affect fracture risk. Advanced engineering concepts will not be presented, but a familiarity with basic mechanical principles is assumed.

Correlation between hand and total body bone density in normal Chinese children

Hand bone mineral density (BMD) in adults was found to be significantly correlated with various skeletal sites, including the total body. However, the relationships between hand and total body bone measurements have yet to be explored for children. We conducted a cross-sectional study of 892 normal Chinese children (511 males, 381 females) aged 5-14 years by measuring the BMD and bone mineral content (BMC) at the total hand, upper limb, subtotal body, and total body using dual-energy X-ray absorptiometry (DXA). We found that hand BMD and BMC increased with age for both genders. Female children had significantly higher hand BMD and BMC than males. Age explained more variance in hand BMD for females (R2=0.727) than for males (R2=0.596). For both genders, hand BMD and BMC correlated highly with age, weight, height, total body lean mass, and BMD and BMC at the upper limb, subtotal body, and total body (r=0.730-0.965, p<0.001) and moderately with body mass index and total body fat mass (r=0.525-0.701, p<0.001). Therefore, the hand DXA scan can potentially be a new tool for the clinical assessment of bone health in children.

Muscle weakness, spasticity and disuse contribute to demineralization and geometric changes in the radius following chronic stroke

Bone health status of the radius in individuals with chronic stroke was evaluated using peripheral quantitative computed tomography. Bone mineral density and cortical thickness on the affected side were compromised when compared with the unaffected side. Muscle weakness, spasticity, and disuse were identified as contributing factors to such changes.

INTRODUCTION

Following a stroke, demineralization and geometric changes occur in bone as a result of disuse and residual impairments, and these can contribute to an increased risk of fragility fractures.

METHODS

This study used peripheral quantitative computed tomography (pQCT) to evaluate volumetric bone mineral density and geometry at the midshaft radius in people living with chronic stroke. Older individuals with chronic stroke were recruited. Each subject underwent a pQCT scan of the midshaft radius at the 30% site on both upper limbs. Muscle strength, motor function, spasticity, and chronic disuse were also evaluated. Data from 47 subjects (19 women) were assessed.

RESULTS

A significant difference was found between the two limbs for cortical bone mineral content, cortical bone mineral density, cortical thickness, and polar stress-strain index. There was no significant side-to-side difference in total bone area. Percent side-to-side difference in muscle strength, spasticity, and chronic disuse were significant determinants of percent side-to-side difference in cortical bone mineral content and cortical thickness.

CONCLUSIONS

The findings suggest that following chronic stroke, endosteal resorption of the midshaft radius occurred with a preservation of total bone area. Muscle weakness, spasticity, chronic disuse significantly contributed to demineralization and geometric changes in the radius following chronic stroke.

Peripheral bone densitometry: Clinical applications

Technologies for the measurement of bone mineral density and other parameters of bone strength at peripheral skeletal sites have been studied since the 1960s. Single-energy Photon Absorptiometry (SPA), Radiographic Absorptiometry (RA), Radiogrametry (RG), Single-energy X-ray Absorptiometry (SXA), Peripheral Dual-energy X-ray Absorptiometry (pDXA), and Quantitative Ultrasonometry (QUS) have been successively evaluated. These technologies and their clinical applications are discussed in this article. The available scientific evidence supports the clinical use of these technologies at peripheral skeletal for assessment of fracture risk. Peripheral measurements other than the 33% (one-third) radius by DXA cannot be used to diagnose osteoporosis according to current standards. Peripheral skeletal sites are not clinically useful for monitoring changes in BMD with natural evolution of the disease and its treatment. Peripheral BMD measurement can theoretically be used to screen patients for selection to central DXA testing, although device-specific cut-points should be developed before this is implemented. When central DXA testing is not available, peripheral BMD testing may be considered to identify individuals who might benefit from pharmacological intervention.

Age-related changes in trabecular architecture differ in female and male C57BL/6J mice

We used microCT and histomorphometry to assess age-related changes in bone architecture in male and female C57BL/6J mice. Deterioration in vertebral and femoral trabecular microarchitecture begins early, continues throughout life, is more pronounced at the femoral metaphysis than in the vertebrae, and is greater in females than males.

INTRODUCTION

Despite widespread use of mice in the study of musculoskeletal disease, the age-related changes in murine bone structure and the relationship to whole body BMD changes are not well characterized. Thus, we assessed age-related changes in body composition, whole body BMD, and trabecular and cortical microarchitecture at axial and appendicular sites in mice.

MATERIALS AND METHODS

Peripheral DXA was used to assess body composition and whole body BMD in vivo, and microCT and histomorphometry were used to measure trabecular and cortical architecture in excised femora, tibia, and vertebrae in male and female C57BL/6J mice at eight time-points between 1 and 20 mo of age (n = 6-9/group).

RESULTS

Body weight and total body BMD increased with age in male and female, with a marked increase in body fat between 6 and 12 mo of age. In contrast, trabecular bone volume (BV/TV) was greatest at 6-8 wk of age and declined steadily thereafter, particularly in the metaphyseal region of long bones. Age-related declines in BV/TV were greater in female than male. Trabecular bone loss was characterized by a rapid decrease in trabecular number between 2 and 6 mo of age, and a more gradual decline thereafter, whereas trabecular thickness increased slowly over life. Cortical thickness increased markedly from 1 to 3 mo of age and was maintained or slightly decreased thereafter.

CONCLUSIONS

In C57BL/6J mice, despite increasing body weight and total body BMD, age-related declines in vertebral and distal femoral trabecular bone volume occur early and continue throughout life and are more pronounced in females than males. Awareness of these age-related changed in bone morphology are critical for interpreting the skeletal response to pharmacologic interventions or genetic manipulation in mice.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.

Drug insight: the use of bisphosphonates for the prevention and treatment of osteoporosis in men

Osteoporosis has long been recognized as a disease affecting postmenopausal women but it has become increasingly clear that men are affected by low bone density and suffer the consequences of osteoporotic fractures. Men attending clinical urological practices might be at raised risk of bone loss due to hypogonadism, either identified during work-up of erectile dysfunction or induced by androgen deprivation therapy for treatment of prostate cancer. The availability of bisphosphonate drugs with proven efficacy in fracture reduction has revolutionized osteoporosis therapy in the past decade. The use of these agents has been traditionally based on data obtained predominantly from postmenopausal women and cases of glucocorticoid-induced osteoporosis, but data are becoming increasingly available to justify their use in men. Despite the availability and favorable safety profile of bisphosphonates, many patients are not receiving therapy. This article serves to review the data regarding bisphosphonate use in men, discussing particularly the pharmacology and mechanisms of action of these agents, and findings from clinical studies supporting their use for fracture prevention.

Normal reference for bone density in healthy Chinese children

An ethnicity- and gender-specific normal reference database is necessary for the clinical dual-energy X-ray absorptiometry (DXA) assessment of skeletal status in Chinese children. We used a Lunar Prodigy DXA densitometer to measure bone mineral density (BMD), bone mineral content (BMC), and bone area (BA) at total body and subcranial skeleton for 877 healthy Chinese children (505 boys, 372 girls) aged 5-13 yr. The height-for-age, BA-for-height, and BMC-for-BA percentile curves were developed using the LMS method (L, power in Box-Cox transformation; M, median; S, coefficient of variation). We found that total body BMD and subcranial skeleton BMD were highly correlated (r=0.701-0.949), and that total body BMD was significantly higher than subcranial skeleton BMD for each gender and age group (p<0.001). No gender differences in total body and subcranial skeleton BMD were found. Total body lean mass correlated highly with total body BMC and subcranial skeleton BMD and BMC (boys: r=0.888-0.953, girls: r=0.917-0.967) and moderately with total body BMD (boys: r=0.684, girls: r=0.777). The head region accounted for 16-52% and 16-49% of the total body BMC in boys and girls, respectively, and the percentages were negatively correlated with age (boys: r=-0.824, girls: r=-0.864) and height (boys: r=-0.911, girls: r=-0.922). Regression analyses showed that age explained more variance in subcranial skeleton BMD (boys: R(2)=0.641, girls: R(2)=0.685) than in total body BMD (boys: R(2)=0.387, girls: R(2)=0.472). In summary, we have presented an ethnicity- and gender-specific densitometric normal reference database for Chinese children aged 5-13 yr. It should allow for an appropriate clinical assessment of total body bone density in Chinese children as measured by the Lunar Prodigy DXA densitometer.

Effect of female database use for T-score derivation in men

Whether to use male or female databases to obtain T-scores in men remains controversial. This study evaluated the impact of deriving male T-scores using female databases in 350 men aged 22.8-93.5 (mean 67.5+/-12.2) yr who were referred for clinically indicated dual-energy X-ray absorptiometry exams. Spine, femur, and nondominant radius scans were obtained in routine clinical manner using a GE Healthcare Lunar Prodigy densitometer. Analyses were performed using software version 9.30. Initially, the GE Healthcare Lunar male normative database was used to calculate T-scores. Subsequently, scans were reanalyzed using female databases; GE for the spine and radius, and NHANES III for the femur. Using the manufacturer's male database, T-scores (mean [range]) of the L1-4 spine, femur neck, total femur, and .3 radius were 0.0 [-4.6 to +8.5], -1.6 [-4.3 to +2.3], -1.1 [-4.0 to +3.3], and -0.7 [-5.3 to +2.9], respectively. On reanalysis with female databases, T-scores "improved" (p<0.0001) with a positive bias of 0.34, 0.33, 0.58, and 1.20, respectively at the above 4 sites. Using female databases, the proportion of men classified as having normal bone mass increased from 22% to 33% and those identified as osteoporotic decreased from 29% to 17%. If pharmacologic treatment were prescribed at a T-score <-2.0, use of the female databases would reduce those treated for low bone mass from 46% to 32%. In conclusion, using female databases to derive male T-scores results in "improvement" of diagnostic classification for a substantial number of men with fewer being classified as having low bone mass.

Osteoporosis in men: Pathophysiology and treatment

Osteoporosis has long been long considered a disease of the aging female skeleton. However, it is now clear that men are also at risk for this disorder. Epidemiologic studies have confirmed that osteoporotic fractures in men are an increasing public health problem, in part due to increased longevity and increased public awareness. Recent large-scale population studies in men have led to advances in our understanding of bone fragility and its treatment in men. This article reviews what is known about the factors in men that lead to acquisition, maintenance, and loss of bone, as well as new insights into causes, pathogenesis, and treatment of osteoporosis in men.

Osteoporosis in men

Osteoporosis has long been considered to be a disease of the aging female skeleton. As awareness of the pervasiveness of this disorder increases, it is clear that men are also at risk for this disorder. Recent epidemiological studies have confirmed that osteoporosis in men is an increasing health problem. This development not only has its roots in increased longevity but also in increased awareness of this problem in men. The purpose of this article is to review what is known about the factors in men that lead to acquisition, maintenance, and loss of bone, as well as new insights about the causes, pathogenesis, and treatment of osteoporosis in men.

Skeletal effects of long-term estrogen and testosterone replacement treatment in a man with congenital aromatase deficiency: evidences of a priming effect of estrogen for sex steroids action on bone

The relative contribution of each sex steroid (i.e. estrogen and androgen) on bone in men and the relationships among sex steroids and changes in BMD and bone strength are still unknown. A defective BMD of bone tissue is constantly present in men with aromatase deficiency. This study evaluates the effects of different regimens of treatment with sex steroids over 7.3 years follow-up on BMD in an adult man affected by aromatase deficiency and by a concomitant mild hypogonadism, as previously described. The aim of the study is to provide additional data on the relative roles of androgens and estrogens in male bone metabolism. The effects of testosterone (T) treatment alone and estrogen (tE(2)) treatment alone as well as the effects of the combined treatment with testosterone and estradiol (T plus tE(2)) on areal BMD (aBMD) at dual-energy X-ray absorptiometry (DXA) and the effects of T plus tE(2) on volumetric BMD (vBMD), particular at cortical site, measured by peripheral quantitative computed tomography (pQCT), are investigated. Hormones and markers of bone turnover were monitored during all phases of the study. Treatment with tE(2) normalized serum estradiol, but only the combined treatment with T plus tE(2) normalized both serum estradiol and testosterone. Markers of bone turnover reached a pattern close to normality during T plus tE(2). The aBMD was little modified by T, but increased more during tE(2). T plus tE(2) resulted in a further increase in both aBMD at DXA and vBMD at pQCT. Cortical thickness increased during T plus tE(2) both in radius and tibia. Only the combined treatment led to optimal parameters of aBMD suggesting that testosterone needs estrogens as a permissive factor for a direct androgen anabolic action on bone in men.

Bone loss in elderly men: increased endosteal bone loss and stable periosteal apposition. The prospective MINOS study

INTRODUCTION

Longitudinal studies on the age-related bone loss in men concerns the decrease in areal bone mineral density (aBMD), which can be qualified as "apparent bone loss" because it does not reflect the change in bone mineral content (BMC). Loss of BMC can be referred to as "net bone loss" because it does not take into account the morphological basis of the bone loss (decreased periosteal apposition; endosteal bone loss, i.e. bone loss on the trabecular, endocortical and intracortical surfaces). The aim of this study was to assess age-related apparent net and endosteal bone loss as well as their morphological basis and age-related changes during a prospective follow-up in a large cohort of elderly men.

METHODS

This analysis was performed in 725 men aged 51-85 at baseline who were followed up for 90 months.

RESULTS

Bone densitometry was carried out at the lumbar spine, hip and whole body by using the HOLOGIC QDR1500 device and at the distal forearm by using the Osteometer DTX100 device. Sixty-five men who abandoned the study after the first examination were older and had lower aBMC at most sites of measurement. Apparent bone loss was significant at the hip, distal forearm and whole body. Net bone loss was also significant at these sites, except for the femoral neck. Periosteal expansion was significant at all sites of measurement. Apparent and net bone loss accelerated with age, whereas the rate of periosteal expansion remained stable. At the distal radius and ulna, endosteal bone loss accelerated with age, whereas the rate of periosteal apposition remained stable.

CONCLUSION

In a large cohort of elderly men, age-related apparent bone loss (aBMD) at the hip, distal forearm and whole body was determined by the net bone loss (BMC), except for the femoral neck. Apparent and net bone loss accelerated with age, whereas the periosteal expansion rate (bone widening) remained constant. At the distal forearm, age-related acceleration of the apparent bone loss was determined by the higher endosteal bone loss, whereas the periosteal apposition rate (estimated mass of deposited bone) remained constant.

Genetic and environmental determinants of volumetric and areal BMD in multi-generational families of African ancestry: the Tobago Family Health Study

BMD is higher and fracture risk is lower among individuals of African versus European descent, but little is known about the genetic architecture of BMD in the former group. Heritabilities of areal and volumetric BMD were moderate in our large families of African descent but differed for trabecular and cortical BMD.

INTRODUCTION

Populations of African ancestry have lower osteoporotic fracture risk and higher BMD than other ethnic groups. However, there is a paucity of information regarding the genetic and environmental influences on bone health among populations of African heritage.

MATERIALS AND METHODS

We dissected the genetic architecture of areal BMD measured by DXA at the proximal femur, lumbar spine, and whole body and volumetric BMD measured by pQCT at the distal and proximal radius and tibia in 283 women and 188 men > or =18 years of age (mean, 43 years) from eight multigenerational Afro-Caribbean families (mean family size > 50). Using quantitative genetic methods, we estimated the residual heritability and the effects of anthropometric, demographic, lifestyle, and medical variables on areal and volumetric BMD.

RESULTS

Compared with U.S. non-Hispanic blacks and whites, areal BMD at the femoral neck was highest in the Afro-Caribbean men and women at all ages. Trabecular volumetric BMD decreased linearly with increasing age, whereas cortical volumetric BMD did not decrease until age 40-49, especially in women. Anthropometric, lifestyle, and medical factors accounted for 12-32% of the variation in areal and volumetric BMD, and residual heritabilities (range, 0.23-0.52) were similar to those reported in other ethnic groups. Heritability of cortical BMD was substantially lower than that of areal or trabecular volumetric BMD, although the measured covariates accounted for a similar proportion of the total phenotypic variation.

CONCLUSIONS

Our study is the first comprehensive genetic epidemiologic analysis of volumetric BMD measured by QCT and the first analysis of these traits in extended families of African descent. Genes account for as much or more of the total variation in areal and volumetric BMD than do environmental factors, but these effects seem to differ for trabecular and cortical bone.

Fragile external phenotype of modern human proximal femur in comparison with medieval bone

Proximal femur macroanatomy of 118 medieval and 67 contemporary adults, 84 contemporary elderly, and 48 contemporary hip fracture cases was evaluated. Within approximately 1000 years, the femoral neck axis has become longer, and its cross-section has become proportionally smaller and more oval in shape. These changes in the present external phenotype alone account for approximately 50% higher fall-induced stress compared with the medieval situation.

INTRODUCTION

Bones, as whole skeletal structures, adapt to mechanical stresses they customarily experience. Because the present, mechanized lifestyle apparently deprives our skeletons of vigorous, habitual physical exertion, we studied whether the proximal femur phenotype has evolved vulnerable to fragility fractures by time.

MATERIALS AND METHODS

Proximal femur macroanatomy of 118 medieval and 67 contemporary adults, 84 contemporary elderly, and 48 contemporary hip fracture cases was evaluated. Using direct measurements of external bone dimensions and geometric properties, we estimated the fall-induced stress as an index of hip fragility.

RESULTS

Within approximately 1000 years, the femoral axis length has become substantially longer (analysis of covariance, body height adjusted, p < 0.001), whereas the neck circumference has not increased. The macroanatomy was found similar between the contemporary adult and elderly groups. In hip fracture cases, however, the femoral axis length was further lengthened (p < 0.001), but the circumference was somewhat smaller (p = 0.001). Consequently, the estimated fall-induced stress can be approximately 1.5-fold today compared with the medieval times (p < 0.001), and the secular trend seemed to be worse in women (sex-time interaction, p = 0.001).

CONCLUSIONS

The modern, relatively slender phenotype of the proximal femur alone seems to increase the fall-induced stress considerably, and when this phenotype coincides the osteoporotic, internally deteriorated femoral neck structure, fracture risk is imminent. This mechanically compromised external phenotype underscores the importance of timely strengthening of the skeleton and its regular maintenance throughout life.

Structural and functional assessment of trabecular and cortical bone by micro magnetic resonance imaging

Osteoporosis is a multifactorial disorder of bone mineral homeostasis affecting the elderly. It is a major public health issue with significant socioeconomic consequences. Recent findings suggest that bone loss-the key manifestation of the disease-is accompanied by architectural deterioration, both affecting the bone's mechanical competence and susceptibility to fracture. This article reviews the potential of quantitative micro MRI (mu-MRI), including a discussion of the technical requirements for image acquisition, processing, and analysis for assessing the architectural implications of osteoporosis and as a means to monitor the response to treatment. With current technology, the resolution achievable in clinically acceptable scan times and necessary signal-to-noise ratio (SNR) is comparable to trabecular thickness. This limited spatial resolution regime demands processing and analysis algorithms designed to operate under such limiting conditions. It is shown that three different classes of structural parameters can be distinguished, characterizing scale, topology, and orientation. There is considerable evidence that osteoporotic bone loss affects all three classes but that topological changes, resulting from conversion of trabecular plates to rods, with the latter's eventual disconnection, are particularly prominent. Clinical applications discussed can be divided into those dealing with assessment of osteoporotic fracture risk as opposed to the study of the effect of disease progression and regression in response to treatment. Current data suggest that noninvasive assessment of cortical and trabecular bone (TB) architecture by mu-MRI may provide new surrogate endpoints to assess the efficacy of intervention in osteoporosis treatment and prevention.

Mechanical characteristics of cortical bone pins designed for fracture fixation

Pins constructed from cortical bone may provide a reasonable alternative to other fracture-fixation devices by circumventing some of the complications associated with stainless steel and synthetic biodegradable implants. However, it is unknown whether cortical bone pins provide comparable strength compared to conventional pins. Using four-point bending, we compared the mechanical characteristics of 1.2-mm allogeneic cortical bone pins milled from specific regions of human tibiae and femora to commercially available 1.1-mm diameter stainless steel pins and 1.3-mm diameter polydioxanone pins. We used impact testing to identify mechanical differences in cortical bone pins between gender and harvest site. Cortical bone pins had better mechanical properties in four-point bending compared with polydioxanone pins, but not stainless steel pins. Pins milled from the right tibiae of males had the best bending characteristics. The mechanical performance of 1.2-mm cortical bone pins was comparable to those of stainless steel and polydioxanone pins regardless of site, bone, and gender. The clinical investigation of cortical bone pins as an implant for fracture fixation is warranted based on mechanical testing and comparison to commercially available polydioxanone and stainless steel pins.