Ageing Effects on 3-Dimensional Femoral Neck Cross-Sectional Asymmetry: Implications for Age-Related Bone Fragility in Falling

This paper explores the effects of aging on femoral neck (FN) anatomy in a study of women aged 20–90years in relation to implications for FN fracture propensity in buckling. Five hundred and four participants were scanned by Quantitative Computed Tomography and analyzed using Quantitative Computed Tomography Pro BIT (Mindways). FN cross-section was split through geometric center into superior and inferior sectors. Bone mass, structural measurements, and bone mineral density were analyzed. Buckling ratio was calculated as ratio of buckling radius to cortical thickness. Between 2nd decade and 8th decade, age-related integral bone mass reduction in superior sector was substantially larger than in inferior sector (33% compared to 21%), especially in cortical bone superiorly compared to inferiorly (53% vs 21%; p < 0.001), principally due to reduction in cortical thickness, averaged cortical thickness (56%) with little difference in density. Superior and inferior sector trabecular bone mineral density reduction was similar at 41% and 43% respectively. Differential cortical bone loss in superior sector resulted in a 59% inferior displacement (δ) of center-of-mass from geometric center. Differences in δ and averaged cortical thickness with age accounted for a 151% increase in mean superior buckling ratio from 9 to 23. Analysis confirms significant progressive age-related superior cortical bone loss as the major age effect on FN structure with relative preservation of inferior cortex probably related to maintenance of inferior sector by regular loading as a result of standing and walking. Computation of buckling ratio may allow prediction of fracture propensity in a sideways fall.     

Proximal femoral density and geometry measurements by quantitative computed tomography: association with hip fracture

INTRODUCTION: Bone mineral density and geometry measurements by volumetric quantitative computed tomography (vQCT) have been utilized in clinical research studies of aging, pharmacologic intervention and mechanical unloading, but there is relatively little information about the association of these measures with hip fracture. To address this issue, we have carried out a study comparing vQCT parameters in elderly Chinese women with hip fractures with measurements in age-matched controls. MATERIALS AND METHODS: Forty-five women (mean age 74.71+/-5.94) with hip fractures were compared to 66 age-matched control subjects (mean age 70.70+/-4.66). vQCT was employed to characterize the volumetric bone mineral density in cortical, trabecular, and integral volumes of interest in the proximal femur. In addition to the volume of interest measurements, we computed the cross-sectional areas of the femoral neck and intertrochanteric planes, the femoral neck axis length, indices of femoral neck bending and compressive strength, and measures of femoral neck cortical geometry. To determine if cortical geometry measures were associated with hip fracture independently of trabecular vBMD, we carried out multi-variate analyses including these parameters in a logistic regression model. RESULTS AND CONCLUSIONS: All vQCT measurements discriminated between fractured subjects and age-matched controls. There was no significant difference in predictive strength between volumetric and areal representations of BMD and trabecular and integral vBMD showed comparable discriminatory power, although both of these measures were more correlated to fracture status than cortical vBMD. We found that fractured subjects had larger femoral neck cross-sectional areas, consistent with adaptation to lower BMD in these osteoporotic subjects. The larger neck cross-sectional areas resulted in bending strength indices in the fractured subjects that were comparable or larger than those of the control subjects. In multi-variate analyses, reduced femoral neck cortical thickness and buckling ratio indices were associated with fracture status independently of trabecular vBMD.     

Hip Fractures and the Contribution of Cortical Versus Trabecular Bone to Femoral Neck Strength

Osteoporotic fractures are caused by both cortical thinning and trabecular bone loss. Both are seen to be important for bone fragility. The relative contributions of cortical versus trabecular bone have not been established. The aim of this study was to test the contribution of cortical versus trabecular bone to femoral neck stability in bone strength. In one femur from each pair of 18 human cadaver femurs (5 female; 4 male), trabecular bone was completely removed from the femoral neck, providing one bone with intact and the other without any trabecular structure in the femoral neck. Geometrical, X‐ray, and DXA measurements were carried out before biomechanical testing (forces to fracture). Femoral necks were osteotomized, slices were analyzed for cross‐sectional area (CSA) and cross‐sectional moment of inertia (CSMI), and results were compared with biomechanical testing data. Differences between forces needed to fracture excavated and intact femurs (ΔF/F mean) was 7.0% on the average (range, 4.6–17.3%). CSA of removed spongiosa did not correlate with difference of fracture load (ΔF/F mean), nor did BMD. The relative contribution of trabecular versus cortical bone in respect to bone strength in the femoral neck seems to be marginal and seems to explain the subordinate role of trabecular bone and its changes in fracture risk and the effects of treatment options in preventing fractures.     

In vivo discrimination of hip fracture with quantitative computed tomography: Results from the prospective European Femur Fracture Study (EFFECT)

In assessing osteoporotic fractures of the proximal femur, the main objective of this in vivo case‐control study was to evaluate the performance of quantitative computed tomography (QCT) and a dedicated 3D image analysis tool [Medical Image Analysis Framework—Femur option (MIAF‐Femur)] in differentiating hip fracture and non–hip fracture subjects. One‐hundred and seven women were recruited in the study, 47 women (mean age 81.6 years) with low‐energy hip fractures and 60 female non–hip fracture control subjects (mean age 73.4 years). Bone mineral density (BMD) and geometric variables of cortical and trabecular bone in the femoral head and neck, trochanteric, and intertrochanteric regions and proximal shaft were assessed using QCT and MIAF‐Femur. Areal BMD (aBMD) was assessed using dual‐energy X‐ray absorptiometry (DXA) in 96 (37 hip fracture and 59 non–hip fracture subjects) of the 107 patients. Logistic regressions were computed to extract the best discriminates of hip fracture, and area under the receiver characteristic operating curve (AUC) was calculated. Three logistic models that discriminated the occurrence of hip fracture with QCT variables were obtained (AUC = 0.84). All three models combined one densitometric variable—a trabecular BMD (measured in the femoral head or in the trochanteric region)—and one geometric variable—a cortical thickness value (measured in the femoral neck or proximal shaft). The best discriminant using DXA variables was obtained with total femur aBMD (AUC = 0.80, p = .003). Results highlight a synergistic contribution of trabecular and cortical components in hip fracture risk and the utility of assessing QCT BMD of the femoral head for improved understanding and possible insights into prevention of hip fractures. © 2011 American Society for Bone and Mineral Research.     

Similarities and differences between sexes in regional loss of cortical and trabecular bone in the mid‐femoral neck: The AGES‐Reykjavik longitudinal study

The risk of hip fracture rises rapidly with age, and is notably higher in women. After falls and prior fragility fractures, the main clinically recognized risk factor for hip fracture is reduced bone density. To better understand the extent to which femoral neck density and structure change with age in each sex, we carried out a longitudinal study in subjects not treated with agents known to influence bone mineral density (BMD), to investigate changes in regional cortical thickness, as well as cortical and trabecular BMD at the mid‐femoral neck. Segmental quantitative computed tomography (QCT) analysis was used to assess bone measurements in two anatomic subregions, the superolateral (superior) and inferomedial (inferior). A total of 400 older individuals (100 men and 300 women, aged 66–90 years) who were participants in the Age Gene/Environment Susceptibility‐Reykjavik Study (AGES‐Reykjavik), were studied. Participants had two QCT scans of the hip over a median follow‐up of 5.1 years (mean baseline age 74 years). Changes in bone values during follow‐up were estimated from mixed effects regression models. At baseline women had lower bone values in the superior region than men. At follow‐up all bone values were lower in women, except cortical volumetric bone mineral density (vBMD) inferiorly. The relative losses in all bone values estimated in the superior region were substantially (about threefold) and significantly greater compared to those estimated in the inferior region in both sexes. Women lost cortical thickness and cortical vBMD more rapidly than men in both regions; and this was only weakly reflected in total femoral neck dual‐energy X‐ray absorptiometry (DXA)‐like results. The higher rate of bone loss in women at critical locations may contribute materially to the greater femoral neck fracture incidence among women than men. © 2013 American Society for Bone and Mineral Research.     

Biomechanical indices of the femoral neck estimated from the standard DXA output: age- and sex-related differences.

We explored the feasibility of using routine dual-energy X-ray absorptiometry (DXA) to estimate several parameters of femoral neck geometry related to bone strength and to analyze their changes with age. Bone mineral density (BMD) was measured in 871 control men and women and in 19 women with hip fracture. Volumetric BMD (volBMD) and geometrical parameters were estimated from the DXA output with previously published formulas. In young subjects, areal BMD was higher in men than in women, but volBMD was similar in both sexes. However, it showed a more rapid decline with age in women. The femoral neck width and cortical thickness were also higher in young men than in women. Neck width increased and cortical thickness decreased with age in both sexes. The buckling ratio, an index of local cortical instability, increased more rapidly in women. The compressive strength decreased progressively with age in women, whereas it did not change in men after 50 yr of age. Compressive strength and the buckling ratio showed the largest difference between control and hip fracture women (Z=-1.3). This cross-sectional study suggests that data available in the standard DXA output can easily be used to estimate several geometrical parameters of the femoral neck that evolve in a sex- and age-specific manner. Further studies are needed to elucidate whether they add significant information to BMD in the prediction of fracture risk.     

年龄对股骨颈骨密度和皮质厚度的影响

目的观察年龄对股骨颈骨密度和皮质厚度的影响,及与股骨颈骨折的关系。方法对73例50岁以上因髋关节疾病住院病人行股骨近段CT扫描和DXA髋部骨密度测定,分为50～65岁组、66～80岁组和>80岁组,以股骨颈骨密度为标准判断骨质疏松程度,以皮质比率作为评估皮质厚度的标准。结果股骨颈骨密度:50～65岁组为0.710±0.139、66～80岁组为0.613±0.104和>80岁组为0.572±0.061。66～80岁组和>80岁组与50～65岁组有非常显著性差异,66～80岁组与>80岁组差异无统计学意义。T20长径皮质比率:50～65岁组与66～80岁组差异无统计学意义,而66～80岁组与>80岁组有非常显著性差异。股骨颈宽径皮质比率:50～65岁组与>80岁组有非常显著性差异。结论股骨颈骨密度和皮质厚度随年龄增高而降低,提示股骨颈皮质厚度变薄是高龄髋部骨折风险高的原因之一。     

Changing structure of the femoral neck across the adult female lifespan

The anatomic distribution of cortical and cancellous bone in the femoral neck may be critical in determining resistance to fracture. We investigated the effects of aging on femoral neck bone in women. In this cross‐sectional study, we used clinical multidetector computed tomography (MDCT) of the hips to investigate aging effects in 100 female volunteers aged 20 to 90 years. We developed a clinically efficient protocol to measure cortical thickness (C.Th) and cortical, trabecular, and integral bone mineral density (CtBMD, TrBMD, and iBMD in mg/cm³) in anatomic quadrants of the femoral neck. We used a nested ANOVA to evaluate their associations with height, weight, location in the femoral neck, and age of the subject. Age was the principal determinant of both cortical thickness and BMD. Age had significantly different effects within the anatomic quadrants; compared with young women, elderly subjects had relative preservation of the inferoanterior (IA) quadrant but strikingly reduced C.Th and BMD superiorly. A model including height, weight, and region of interest (and their interactions) explained 83% of the measurement variance (p < .0001). There were marked C.Th and BMD differences between age 25 and age 85 in the already thin superior quadrants. At 25 years the predicted C.Th of the superoposterior quadrant was 1.63 mm, whereas at 85 years it was 0.33 mm [?1.33 mm, 95% confidence interval (CI) of difference over 60 years ?1.69 to ?0.95]. By contrast, at 25 years mean C.Th of the IA quadrant was 3.9 mm, whereas at 85 years it was 3.3 mm (?0.6 mm, 95% CI ?0.83 to ?0.10). CtBMD of the IA region was equivalent at 25 and 85 years. In conclusion, elderly women had relative preservation of IA femoral neck bone over seven decades compared with young women but markedly lower C.Th and BMD in the other three quadrants. The IA quadrant transmits mechanical load from walking. Mechanical theory and laboratory tests on cadaveric femurs suggest that localized bone loss may increase the risk of fracture in elderly fallers. It remains to be determined whether this MDCT technique can provide better prediction of hip fracture than conventional clinical dual X‐ray absorptiometry (DXA). © 2010 American Society for Bone and Mineral Research     

Experimental hip fracture load can be predicted from plain radiography by combined analysis of trabecular bone structure and bone geometry

Summary Computerized analysis of the trabecular structure was used to test whether femur failure load can be estimated from radiographs. The study showed that combined analysis of trabecular bone structure and geometry predicts in vitro failure load with similar accuracy as DXA. Introduction Since conventional radiography is widely available with low imaging cost, it is of considerable interest to discover how well bone mechanical competence can be determined using this technology. We tested the hypothesis that the mechanical strength of the femur can be estimated by the combined analysis of the bone trabecular structure and geometry. Methods The sample consisted of 62 cadaver femurs (34 females, 28 males). After radiography and DXA, femora were mechanically tested in side impact configuration. Fracture patterns were classified as being cervical or trochanteric. Computerized image analysis was applied to obtain structure-related trabecular parameters (trabecular bone area, Euler number, homogeneity index, and trabecular main orientation), and set of geometrical variables (neck-shaft angle, medial calcar and femoral shaft cortex thicknesses, and femoral neck axis length). Multiple linear regression analysis was performed to identify the variables that best explain variation in BMD and failure load between subjects. Results In cervical fracture cases, trabecular bone area and femoral neck axis length explained 64% of the variability in failure loads, while femoral neck BMD also explained 64%. In trochanteric fracture cases, Euler number and femoral cortex thickness explained 66% of the variability in failure load, while trochanteric BMD explained 72%. Conclusions Structural parameters of trabecular bone and bone geometry predict in vitro failure loads of the proximal femur with similar accuracy as DXA, when using appropriate image analysis technology.     

Femoral Volumetric Bone Density,Geometry, and Strength in Relation to 25‐Hydroxy Vitamin D in Older Men

Low serum 25‐hydroxy vitamin D (25(OH)D) concentrations are associated with increased hip fracture risk and decreased femoral areal bone mineral density (BMD) among elderly men. Structural dimensions of the proximal femur and volumetric BMD in cortical and trabecular compartments are also associated with hip fracture risk. However, associations of volumetric BMD or structural dimensions with serum 25(OH)D concentrations among older men remain unclear. In a random sample of 1608 men aged ≥65 years from the Osteoporotic Fractures in Men Study (MrOS), baseline serum 25(OH)D concentrations were measured by liquid chromatography/mass spectrometry assays. Femoral neck geometry and volumetric BMD derived from quantitative computed tomography included integral, cortical, and trabecular volumetric BMD; cross‐sectional area; integral and cortical volume; and cortical volume as a percent of integral volume. We studied 888 men with vitamin D, parathyroid hormone (PTH), femoral neck geometry, and BMD measures. Whole‐bone femoral strength and load‐strength ratio from finite element (FE) analysis were also available for 356 men from this sample. Multivariable linear regression was used to estimate least square means of each femoral measure within quartiles of 25(OH)D adjusted for age, race, body mass index, height, latitude, and season of blood draw. Tests of linear trend in the means were performed across increasing quartile of serum 25(OH)D levels. Mean cortical volume (p trend = 0.006) and cortical volume as a percent of integral volume (p trend < 0.001) increased across increasing quartile of 25(OH)D level. However, overall femoral neck size (area and integral volume) did not vary by 25(OH)D level. Femoral neck volumetric BMD measures increased in a graded manner with higher 25(OH)D levels (p trend < 0.001). Femoral strength, but not load‐strength ratio, increased with increasing 25(OH)D. Adjustment for PTH did not materially change these associations. We conclude that in older men, higher levels of endogenous 25(OH)D may increase whole‐bone strength by increasing femoral volumetric BMD and cortical volume. © 2014 American Society for Bone and Mineral Research.     

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.     

Correlates of trabecular and cortical volumetric bone mineral density at the femoral neck and lumbar spine: The osteoporotic fractures in men study (MrOS)

The objective of this cross‐sectional analysis was to examine the correlates of trabecular and cortical volumetric bone mineral density (vBMD) in 3670 community‐dwelling men, mean age 73.6 ± 5.9 years. vBMD was measured by quantitative computed tomography (QCT) and areal BMD by dual‐energy X‐ray absorptiometry (DXA). Demographic, historical, and lifestyle information was obtained by interview, and height, weight, and neuromuscular function were determined by examination. To express the strength of the associations, percent differences (95% confidence interval) were calculated from multivariable linear regression models using the formula 100 (β × unit/mean BMD). Units for continuous variables were chosen to approximate 1 standard deviation (SD). The multivariable linear regression models predicted 15%, 21%, and 20% of the overall variance in trabecular and cortical vBMD of the femoral neck and vBMD of the lumbar spine, respectively. Diabetes was associated with a 16.5% greater trabecular vBMD at the femoral neck and 11% at the lumbar spine but less than 2% for cortical vBMD. For femoral neck trabecular vBMD, the strongest negative correlates were past smoking (?9%), fracture history (?15%), kidney stones (?7%), corticosteroids (?11%), and insulin therapy (?26%). For cortical vBMD, the strongest negative correlate was use of thyroid medication (?2.8%). The strongest negative correlates for lumbar spine trabecular vBMD were fracture history (?5%), antiandrogen use (?19%), height (?8%), and thiazoliainedione use (?22%). Bioavailable estradiol and testosterone levels were positively related and sex hormone–binding globulin was negatively related to trabecular vBMD of the spine. There was no relationship between sex hormones and femoral neck trabecular vBMD. Our conclusion is that correlates of trabecular vBMD and cortical vBMD appear to differ in older men. © 2010 American Society for Bone and Mineral Research     

Proximal Femoral Structure and the Prediction of Hip Fracture in Men: A Large Prospective Study Using QCT

The structure of the femoral neck contributes to hip strength, but the relationship of specific structural features of the hip to hip fracture risk is unclear. The objective of this study is to determine the contribution of structural features and volumetric density of both trabecular and cortical bone in the proximal femur to the prediction of hip fracture in older men. Baseline QCT scans of the hip were obtained in 3347 men ≥65 yr of age enrolled in the Osteoporotic Fractures in Men Study (MrOS). All men were followed prospectively for an average of 5.5 yr. Areal BMD (aBMD) by DXA was also assessed. We determined the associations between QCT‐derived measures of femoral neck structure, volumetric bone density, and hip fracture risk. Forty‐two men sustained incident hip fractures during follow‐up: an overall rate of 2.3/1000 person‐years. Multivariable analyses showed that, among the QCT‐derived measures, lower percent cortical volume (hazard ratio [HR] per SD decrease: 3.2; 95% CI: 2.2–4.6), smaller minimal cross‐sectional area (HR: 1.6; 95% CI: 1.2–2.1), and lower trabecular BMD (HR: 1.7; 95% CI: 1.2–2.4) were independently related to increased hip fracture risk. Femoral neck areal BMD was also strongly related to hip fracture risk (HR: 4.1; 95% CI: 2.7–6.4). In multivariable models, percent cortical volume and minimum cross‐sectional area remained significant predictors of hip fracture risk after adjustment for areal BMD, but overall prediction was not improved by adding QCT parameters to DXA. Specific structural features of the proximal femur were related to an increased risk of hip fracture. Whereas overall hip fracture prediction was not improved relative to aBMD, by adding QCT parameters, these results yield useful information concerning the causation of hip fracture, the evaluation of hip fracture risk, and potential targets for therapeutic intervention.     

Effects of Treatment of Ovariectomized Adult Rhesus Monkeys with Parathyroid Hormone 1-84 for 16 Months on Trabecular and Cortical Bone Structure and Biomechanical Properties of the Proximal Femur

Treatment of monkeys and humans with parathyroid hormone (PTH) 1-84 stimulates skeletal remodeling, which increases trabecular (Tb) bone mineral density (BMD) but decreases cortical (Ct) BMD at locations where these bone types predominate. We report the effects of daily PTH treatment (5, 10, or 25 μg/kg) of ovariectomized (OVX) rhesus monkeys for 16 months on bone structure and biomechanical properties at the proximal femur, a mixed trabecular and cortical bone site. PTH reversed the OVX-induced decrease in BMD measured by dual-energy X-ray absorptiometry at the proximal femur, femoral neck, and distal femur. Peripheral quantitative computed tomography confirmed a significant decrease in Ct.BMD and an increase in Tb.BMD at the total proximal femur and at the proximal and distal femoral metaphyses. The decrease in Ct.BMD resulted primarily from increased area because cortical bone mineral content was unaffected by PTH. Histomorphometry revealed that PTH significantly increased the trabecular bone formation rate (BFR) as well as trabecular bone volume and number. PTH did not affect periosteal or haversian BFR at the femoral neck, but cortical porosity was increased slightly. PTH had no effects on stiffness or peak load measured using a shear test, whereas work-to-failure, the energy required to fracture, was increased significantly. Thus, PTH treatment induced changes in trabecular and cortical bone at the proximal femur that were similar to those occurring at sites where these bone types predominate. Together, the changes had no effect on stiffness or peak load but increased the energy required to break the proximal femur, thereby making it more resistant to fracture.     

系统性红斑狼疮患者髋部骨密度特点分析及与疾病活动度的关系

目的 探讨系统性红斑狼疮（systemic lupussw erythematosus, SLE）患者骨密度的特点和骨折风险性,并分析其骨量变化与疾病活动度的关系。方法 选取2016年8月至2017年9月于我院确诊的SLE患者49例,体检的健康对照人群52名,收集受试者病史及与骨折风险相关的临床资料,采用双能X线骨密度仪测定两组人群股骨的3D骨密度（bone mineral density, BMD）、二维骨密度,探讨SLE骨量降低与疾病活动度的关系。结果 ①与对照组相比,SLE患者髋部骨小梁的体积骨密度明显降低（t= -0.47, P<0.05）,股骨颈前节段、股骨转子侧面、股骨干前节段的皮质厚度均明显降低（t分别为-2.34、-2.10、-2.36, P均<0.05）;②与对照组相比,SLE组患者髋部二维骨密度明显降低（t= -2.64, P<0.05）,且SLE患者骨折风险度明显高于对照组(t=-3.54, P<0.01）;③SLE组患者疾病活动相关的SLE-DAI积分与髋部骨小梁体积骨密度及股骨颈皮质厚度的减低呈正相关（B分别为1 203.32、1.94, P均<0.05）,而与BMD的改变无明显相关性。结论 SLE患者存在明显的骨量流失和骨折风险性增加,骨密度的改变主要表现为骨小梁体积骨密度和二维骨密度的减低,且SLE病情活动度越高,骨小梁体积骨密度越低。积极控制原发病对预防骨质疏松有重要的临床意义。     

The heterogeneity in femoral neck structure and strength

Most measures of femoral neck strength derived using dual‐energy X‐ray absorptiometry or computed tomography (CT) assume the femoral neck is a cylinder with a single cortical thickness. We hypothesized that these simplifications introduce errors in estimating strength and that detailed analyses will identify new parameters that more accurately predict femoral neck strength. High‐resolution CT data were used to evaluate 457 cross‐sectional slices along the femoral neck of 12 postmortem specimens. Cortical morphology was measured in each cross‐section. The distribution of cortical thicknesses was evaluated to determine whether the mean or median better estimated central tendency. Finite‐element models were used to calculate the stresses in each cross‐section resulting from the peak hip joint forces created during a sideways fall. The relationship between cortical morphology and peak bone stress along the femoral neck was analyzed using multivariate regression analysis. In all cross‐sections, cortical thicknesses were non‐normally distributed and skewed toward smaller thicknesses (p < 0.0001). The central tendency of cortical thickness was best estimated by the median, not the mean. Stress increased as the median cortical thickness decreased along the femoral neck. The median, not mean, cortical thickness combined with anterior‐posterior diameter best predicted peak bone stress generated during a sideways fall (R² = 0.66, p < 0.001). Heterogeneity in the structure of the femoral neck determines the diversity of its strength. The median cortical thickness best predicted peak femoral neck stress and is likely to be a relevant predictor of femoral neck fragility. © 2013 American Society for Bone and Mineral Research.     

Race and ethnic variation in proximal femur structure and BMD among older men.

Femoral neck dimensions and vBMD from QCT were compared among 3,305 black, Asian, Hispanic, and white men >or=65 yr of age. All had similar stature-adjusted mean femoral neck volume, but black and Asian men had thicker cortices and higher trabecular vBMD, which may increase bone strength. INTRODUCTION: Hip fracture rates among elderly U.S. black and Asian men are lower than rates among white men. Structural characteristics or volumetric BMD (vBMD), which confer advantages for femoral neck bone strength, may vary by race/ethnicity. However, this topic has not been studied in detail. MATERIALS AND METHODS: In a cross-sectional study, dimensions and vBMD in the femoral neck and shaft were obtained from QCT scans among 3,305 men >or=65 yr of age in the Osteoporotic Fractures in Men (MrOS) study. Femoral neck measures were cross-sectional area; integral, cortical, and medullary volumes and integral, cortical, and trabecular vBMD. Shaft measures were cross-sectional, cortical, and medullary areas and cortical vBMD. Self-reported race/ethnicity was classified as black, Asian, Hispanic, or white. We used multivariable linear regression models with adjustment for age, height, and body mass index to compare means of the outcome measures in black, Asian, and Hispanic men to those in whites. RESULTS: All groups had similar femoral neck integral volume. Among black and Asian men, mean cortical volume as a percent of integral volume was 6% greater, integral vBMD was 6-10% greater, and trabecular vBMD was 33-36% greater than means among whites. Shaft cross-sectional area was similar among blacks, but smaller among Asians, compared with whites. However, mean shaft cortical area was greater among blacks but similar among Asians and whites, resulting in mean cortical thickness being 5% greater among black and Asian men. Blacks also had greater mean cortical vBMD in both the femoral neck and shaft. CONCLUSIONS: Black and Asian men >or=65 yr of age have features in the proximal femur that may confer advantages for bone strength. Specifically, greater cortical thickness and higher trabecular vBMD among black and Asian men could help explain the lower hip fracture rates in these populations. Discerning the mechanisms underlying these differences could provide advances for the prevention and treatment of osteoporosis.     

脆性股骨颈骨折的股骨颈皮质厚度和骨密度改变

目的 研究脆性股骨颈骨折的股骨颈皮质骨厚度和骨密度变化。方法 对76例病人行股骨近端CT扫描,骨质疏松性股骨颈骨折组42 例,非骨折组34 例。取对侧（正常侧）股骨小转子顶点上方20mm（T20）平面CT横截面影像,计算T20长径和股骨颈寛径皮质比率,作为评估皮质厚度的指标;用DXA测量股骨颈骨密度,了解骨质疏松程度。结果 T20长径皮质比率：骨质疏松性股骨颈骨折组：（17.57±3.54）% ;非骨折组：（21.64±3.75）%（P =0.000）;T20股骨颈宽径皮质比率：骨质疏松性股骨颈骨折组：（25.98±5.51）%;非骨折组：(32.89±5.74)%（P=0.000）。骨密度：骨折组：0.590±0.084 g/cm2 ;非骨折组：0.698±0.138g/cm2, , P <0.000。结论 股骨颈皮质变薄和骨密度降低是导致脆性股骨颈骨折重要因素,T20长径皮质比率和T20股骨颈宽径皮质比率是观察股骨颈皮质骨变化的有效指标。     

Structural and biomechanical basis of sexual dimorphism in femoral neck fragility has its origins in growth and aging.

The structural basis for sex differences in femoral neck (FN) fragility was studied in 1196 subjects and 307 patients with hip fracture. The absolute and relative patterns of modeling and remodeling on the periosteal and endocortical envelopes during growth and aging produce changes in FN geometry and structure that results in FN fragility in both sexes and sexual dimorphism in hip fracture risk in old age. INTRODUCTION: Femoral neck (FN) fragility in old age is usually attributed to age-related bone loss, while the sex differences in hip fracture rate are attributed to less bone loss in men than in women. The purpose of this study was to define the structural and biomechanical basis underlying the increase in FN fragility in elderly men and women and the structural basis of sex differences in hip fracture incidence in old age. MATERIALS AND METHODS: We measured FN dimensions and areal bone mineral density in 1196 healthy subjects (801 females) 18-92 years of age and 307 patients (180 females) with hip fracture using DXA. We then used the DXA-derived FN areal bone mineral density (BMD) and measured periosteal diameter to estimate endocortical diameter, cortical thickness, section modulus (a measure of bending strength), and buckling ratio (indices for structural stability). RESULTS: Neither FN cortical thickness nor volumetric density differed in young adult women and men after height and weight adjustment. The sex differences in geometry were confined to the further displacement of the cortex from the FN neutral axis in young men, which produced 13.4% greater bending strength than in young women. Aging amplified this geometric difference; widening of the periosteal and endocortical diameters continued in both sexes but was greater in men, shifting the cortex even further from the neutral axis maintaining bending strength in men, not in women. In both sexes, less age-related periosteal than endocortical widening produced cortical thinning increasing the risk for structural failure by local buckling of the enlarged thin walled FN. Relative to age-matched controls, women and men with hip fractures had reduced cortical thickness, but FN periosteal diameter was increased in women and reduced in men, differences are likely to be originated in growth. CONCLUSIONS: The absolute and relative patterns of modeling and remodeling on the periosteal and endocortical envelopes during growth and aging produce changes in FN diameters, cortical thickness, and geometry that results in FN fragility in both sexes and sexual dimorphism in hip fracture risk in old age.     

Fracture Risk Assessment in Older Adults Using a Combination of Selected Quantitative Computed Tomography Bone Measures: A Subanalysis of the Age,Gene/Environment Susceptibility-Reykjavik Study

Bone mineral density (BMD) and geometric bone measures are individually associated with prevalent osteoporotic fractures. Whether an aggregate of these measures would better associate with fractures has not been examined. We examined relationships between self-reported fractures and selected bone measures acquired by quantitative computerized tomography (QCT), a composite bone score, and QCT-acquired dual-energy X-ray absorptiometry–like total femur BMD in 2110 men and 2682 women in the Age, Gene/Environment Susceptibility-Reykjavik Study. The combined bone score was generated by summing gender-specific Z-scores for 4 QCT measures: vertebral trabecular BMD, femur neck cortical thickness, femur neck trabecular BMD, and femur neck minimal cross-sectional area. Except for the latter measure, lower scores for QCT measures, singly and combined, showed positive (p < 0.05) associations with fractures. Results remained the same in stratified models for participants not taking bone-promoting medication. In women on bone-promoting medication, greater femur neck cortical thickness and trabecular BMD were significantly associated with fracture status. However, the association between fracture and combined bone score was not stronger than the associations between fracture and individual measures or total femur BMD. Thus, the selected measures did not all similarly associate with fracture status and did not appear to have an additive effect on fracture status.