Assessment of the strength of proximal femur in vitro: relationship to femoral bone mineral density and femoral geometry

Bone stiffness and strength at the distal radius can be determined using photon-counting CT

Estimating bone strength aids in osteoporotic fracture risk assessment. Bone strength is usually calculated with a high-resolution CT; however, this modality has limited clinical utility. We demonstrated that clinical photon-counting CT can also be used for bone strength quantification, which facilitates the use of this information in clinical decision-making.

PURPOSE

Quantification of bone strength and microarchitecture at the distal radius with high-resolution peripheral quantitative computed tomography (HR-pQCT) can predict osteoporotic fracture risk independently of dual-energy X-ray absorptiometry. Photon-counting CT (PCCT) is a novel imaging technique with larger fields of view, shorter acquisition times, and similar resolution when compared to HR-pQCT. This study aimed to compare the stiffness and strength of the distal radius computed from PCCT and HR-pQCT images.

METHODS

We evaluated a 10.2 mm section of the distal radius from eight cadaveric forearms scanned with PCCT and HR-pQCT at 0.11 mm and 0.061 mm voxel size, respectively. All CT images were converted to voxel-based linear finite element models. Two material models were used: a segmentation-based model with a fixed Young's modulus of 10 GPa for bone elements, and a density-based model where Young's modulus was assigned on a voxel-by-voxel basis, based on its gray value. Poisson's ratio was set to 0.3 for all elements. Axial compression at 1% apparent strain was applied to quantify stiffness; strength was quantified with the Pistoia criterion. In addition, load sharing between cortical and trabecular bone was quantified.

RESULTS

We found strong correlations between PCCT and HR-pQCT-derived bone stiffness, strength, and cortical and trabecular proportion for segmentation-based models (R2 > 0.911; p < 2e-4). Correlation and agreement were higher for density-based models (R2 > 0.977; p < 4e-6).

CONCLUSION

We demonstrated that PCCT can estimate bone strength with high accuracy and agreement when compared to HR-pQCT. These findings highlight PCCT's potential in assessing fracture risk in osteoporosis. At the same time, PCCT's large field of view enables broader usage, at sites different from peripheral limbs.

The Multifactorial Relationship Between Bone Tissue Water and Stiffness at the Proximal Femur

Bone mechanical function is determined by multiple factors, some of which are still being elucidated. Here, we present a multivariate analysis of the role of bone tissue composition in the proximal femur stiffness of cadaver bones (n = 12, age 44-93). Stiffness was assessed by testing under loading conditions simulating a sideways fall onto the hip. Compositional properties of cortical and trabecular tissues were quantified in femoral neck cross sections by Fourier transform infrared (FTIR) spectroscopy and near infrared (NIR) spectroscopy. In addition, cross-sectional areas and cortical thickness and tissue mineral density (TMD) were measured at the femoral neck. Pearson correlation analysis showed a significant (p < 0.05) negative relationship between bone stiffness and cortical and trabecular water content, both total (r = -0.63) and tightly bound to matrix and mineral (r = -55). Additionally, significant (p < 0.05) positive correlations were found between stiffness and bone area, both total (r = 0.67) and trabecular (r = 0.58). However, linear regression using each of these properties to predict bone stiffness resulted in weak models (R2 = 0.36-0.48). Interestingly, we found markedly stronger models (cross-validated R2 = 0.80-0.92) by using partial least squares (PLS) regression to predict stiffness based on combinations of bone properties. The models with highest R2 values were found when including bone water parameters as explanatory variables, both total and tightly bound, in cortical and trabecular. This study provides new insights by revealing a multifactorial relationship in which higher bone water content across different tissue compartments contributes to lower bone stiffness, highlighting bone water as a potential biomarker of bone quality and proximal femur mechanical function.

Ultra-low dose hip CT-based automated measurement of volumetric bone mineral density at proximal femoral subregions

BACKGROUND

Forty to fifty percent of women and 13%-22% of men experience an osteoporosis-related fragility fracture in their lifetimes. After the age of 50 years, the risk of hip fracture doubles in every 10 years. x-Ray based DXA is currently clinically used to diagnose osteoporosis and predict fracture risk. However, it provides only 2-D representation of bone and is associated with other technical limitations. Thus, alternative methods are needed.

PURPOSE

To develop and evaluate an ultra-low dose (ULD) hip CT-based automated method for assessment of volumetric bone mineral density (vBMD) at proximal femoral subregions.

METHODS

An automated method was developed to segment the proximal femur in ULD hip CT images and delineate femoral subregions. The computational pipeline consists of deep learning (DL)-based computation of femur likelihood map followed by shape model-based femur segmentation and finite element analysis-based warping of a reference subregion labeling onto individual femur shapes. Finally, vBMD is computed over each subregion in the target image using a calibration phantom scan. A total of 100 participants (50 females) were recruited from the Genetic Epidemiology of COPD (COPDGene) study, and ULD hip CT imaging, equivalent to 18 days of background radiation received by U.S. residents, was performed on each participant. Additional hip CT imaging using a clinical protocol was performed on 12 participants and repeat ULD hip CT was acquired on another five participants. ULD CT images from 80 participants were used to train the DL network; ULD CT images of the remaining 20 participants as well as clinical and repeat ULD CT images were used to evaluate the accuracy, generalizability, and reproducibility of segmentation of femoral subregions. Finally, clinical CT and repeat ULD CT images were used to evaluate accuracy and reproducibility of ULD CT-based automated measurements of femoral vBMD.

RESULTS

Dice scores of accuracy (n = 20), reproducibility (n = 5), and generalizability (n = 12) of ULD CT-based automated subregion segmentation were 0.990, 0.982, and 0.977, respectively, for the femoral head and 0.941, 0.970, and 0.960, respectively, for the femoral neck. ULD CT-based regional vBMD showed Pearson and concordance correlation coefficients of 0.994 and 0.977, respectively, and a root-mean-square coefficient of variation (RMSCV) (%) of 1.39% with the clinical CT-derived reference measure. After 3-digit approximation, each of Pearson and concordance correlation coefficients as well as intraclass correlation coefficient (ICC) between baseline and repeat scans were 0.996 with RMSCV of 0.72%. Results of ULD CT-based bone analysis on 100 participants (age (mean ± SD) 73.6 ± 6.6 years) show that males have significantly greater (p < 0.01) vBMD at the femoral head and trochanteric regions than females, while females have moderately greater vBMD (p = 0.05) at the medial half of the femoral neck than males.

CONCLUSION

Deep learning, combined with shape model and finite element analysis, offers an accurate, reproducible, and generalizable algorithm for automated segmentation of the proximal femur and anatomic femoral subregions using ULD hip CT images. ULD CT-based regional measures of femoral vBMD are accurate and reproducible and demonstrate regional differences between males and females.

Age- and Sex-Related Volumetric Density Differences in Trabecular and Cortical Bone of the Proximal Femur in Healthy Population

BACKGROUND

There are age- and sex-related increases in the prevalence of osteoporosis. Bone densitometry based on dual energy X-ray absorptiometry (DXA) is the gold standard for the assessment of bone mineral density (BMD). Three-dimensional (3D) analysis of the proximal femur (3D-DXA) allows discrimination between cortical and trabecular compartments, and it has shown a good correlation with computed tomography. We aimed to assess age- and sex-related volumetric density differences in trabecular and cortical bone using 3D-DXA and determine the reference intervals for integral volumetric (v)BMD within the Argentine population.

METHODS

Healthy female and male adult subjects (N=1,354) from Argentina were included. Hip BMD was measured using DXA, and 3D analysis was performed using 3D-Shaper software. The integral vBMD, cortical surface BMD, and trabecular vBMD (trab vBMD) were measured.

RESULTS

The study population included 73.9% women (N=1,001) and 26.13% men (N=353). We found a significant decrease in integral vBMD between 20 and 90 years in both sexes (women, -23.1%; men, -16.6%). Bone loss indicated in the integral vBMD results was mainly due to a decrease in trabecular bone in both sexes (women, -33.4%; men, -27.7%). The age-related loss of cortical bone density was less and was limited to the female population, without no age-related differences in men. Moreover, 3D-DXA allowed us to propose reference intervals for integral vBMD.

CONCLUSIONS

We found age- and sex-related bone loss between 20 and 90 years in an Argentine cohort via integral vBMD measurements using 3D-DXA, mainly due to decreases in trabecular bone in both sexes. The age-related loss of cortical bone density was less and was limited to the female population.

Influence of test paradigm on loading dynamics during proximal femur fracture tests simulating sideways falls

Fall-related hip fractures are a serious public health issue in older adults. As most mechanistic hip fracture risk prediction models incorporate tissue tolerance, test methods that can accurately characterize the fracture force of the femur (and factors that influence it) are imperative. While bone possesses viscoelastic properties, experimental characterization of rate-dependencies has been inconsistent in the whole-femur literature. The goal of this study was to investigate the influence of experimental paradigm on loading rate and fracture force (both means and variability) during mechanical tests simulating lateral fall loadings on the proximal femur. Six pairs of matched femurs were split randomly between two test paradigms: a 'lower rate' materials testing system (MTS) with a constant displacement rate of 60 mm/s, and a hip impact test system (HIT) comprised of a custom-built vertical drop tower utilizing an impact velocity of 4 m/s. The loading rate was 88-fold higher for the HIT (mean (SD) = 2465.49 (807.38) kN/s) compared to the MTS (27.78 (10.03) kN/s) paradigm. However, no difference in fracture force was observed between test paradigms (mean (SD) = 4096.4 (1272.6) N for HIT, and 3641.3 (1285.8) N for MTS). Within-paradigm variability was not significantly different across paradigms for either loading rate or fracture force (coefficients of variation ranging from 0.311 to 0.361). Within each test paradigm, significant positive relationships were observed between loading rate and fracture force (HIT adjusted R2 = 0.833, p = 0.007; MTS adjusted R2 = 0.983, p < 0.0001). Overall, this study provides evidence that energy-based impact simulators can be a valid method to measure femoral bone strength in the context of fall-related hip fractures. This study motivates future research to characterize potential non-linear relationships between loading rate and fracture threshold at both macro and microscales.

Lysine-rich rice partially enhanced the growth and development of skeletal system with better skeletal microarchitecture in young rats

Rice is the primary staple food for half of the world's population but is low in lysine content. Previously, we developed transgenic rice with enhanced free lysine content in rice seeds (lysine-rich rice), which was shown safe for consumption and improved the growth in rats. However, the effects of lysine-rich rice on skeletal growth and development remained unknown. In this study, we hypothesized that lysine-rich rice improved skeletal growth and development in weaning rats. Male weaning Sprague-Dawley rats received lysine-rich rice (HFL) diet, wild-type rice (WT) diet, or wild-type rice with various contents of lysine supplementation diet for 70 days. Bone microarchitectures were examined by microcomputed tomography, bone strength was investigated by mechanical test, and dynamics of bone growth were examined by histomorphometric analysis. In addition, we explored the molecular mechanism of lysine and skeletal growth through biochemical testing of growth hormone, bone turnover marker, and amino acid content of rat serum analysis, as well as in a cell culture system. Results indicated that the HFL diet improved rats' bone growth, strength, and microarchitecture compared with the WT diet group. In addition, the HFL diet increased the serum essential amino acids, growth hormone (insulin-like growth factor-1), and bone formation marker concentrations. The cell culture model showed that lysine deficiency reduced insulin-like growth factor-1 and Osterix expression, Akt/mammalian target of rapamycin signaling, and matrix mineralization, and inhibited osteoblast differentiation associated with bone growth. Our findings showed that lysine-rich rice improved skeletal growth and development in weaning rats. A further increase of rice lysine content is highly desirable to fully optimize bone growth and development.

Characterizing Bone Phenotypes Related to Skeletal Fragility Using Advanced Medical Imaging

PURPOSE OF REVIEW

Summarize the recent literature that investigates how advanced medical imaging has contributed to our understanding of skeletal phenotypes and fracture risk across the lifespan.

RECENT FINDINGS

Characterization of bone phenotypes on the macro-scale using advanced imaging has shown that while wide bones are generally stronger than narrow bones, they may be more susceptible to age-related declines in bone strength. On the micro-scale, HR-pQCT has been used to identify bone microarchitecture phenotypes that improve stratification of fracture risk based on phenotype-specific risk factors. Adolescence is a key phase for bone development, with distinct sex-specific growth patterns and significant within-sex bone property variability. However, longitudinal studies are needed to evaluate how early skeletal growth impacts adult bone phenotypes and fracture risk. Metabolic and rare bone diseases amplify fracture risk, but the interplay between bone phenotypes and disease remains unclear. Although bone phenotyping is a promising approach to improve fracture risk assessment, the clinical availability of advanced imaging is still limited. Consequently, alternative strategies for assessing and managing fracture risk include vertebral fracture assessment from clinically available medical imaging modalities/techniques or from fracture risk assessment tools based on clinical risk factors. Bone fragility is not solely determined by its density but by a combination of bone geometry, distribution of bone mass, microarchitecture, and the intrinsic material properties of bone tissue. As such, different individuals can exhibit distinct bone phenotypes, which may predispose them to be more vulnerable or resilient to certain perturbations that influence bone strength.

Multi-view information fusion using multi-view variational autoencoder to predict proximal femoral fracture load

Background

Hip fracture occurs when an applied force exceeds the force that the proximal femur can support (the fracture load or "strength") and can have devastating consequences with poor functional outcomes. Proximal femoral strengths for specific loading conditions can be computed by subject-specific finite element analysis (FEA) using quantitative computerized tomography (QCT) images. However, the radiation and availability of QCT limit its clinical usability. Alternative low-dose and widely available measurements, such as dual energy X-ray absorptiometry (DXA) and genetic factors, would be preferable for bone strength assessment. The aim of this paper is to design a deep learning-based model to predict proximal femoral strength using multi-view information fusion.

Results

We developed new models using multi-view variational autoencoder (MVAE) for feature representation learning and a product of expert (PoE) model for multi-view information fusion. We applied the proposed models to an in-house Louisiana Osteoporosis Study (LOS) cohort with 931 male subjects, including 345 African Americans and 586 Caucasians. We performed genome-wide association studies (GWAS) to select 256 genetic variants with the lowest p-values for each proximal femoral strength and integrated whole genome sequence (WGS) features and DXA-derived imaging features to predict proximal femoral strength. The best prediction model for fall fracture load was acquired by integrating WGS features and DXA-derived imaging features. The designed models achieved the mean absolute percentage error of 18.04%, 6.84% and 7.95% for predicting proximal femoral fracture loads using linear models of fall loading, nonlinear models of fall loading, and nonlinear models of stance loading, respectively.

Conclusion

The proposed models are capable of predicting proximal femoral strength using WGS features and DXA-derived imaging features. Though this tool is not a substitute for predicting FEA using QCT images, it would make improved assessment of hip fracture risk more widely available while avoiding the increased radiation exposure from QCT.

Impact forces in backward falls: Subject-specific video-based rigid body simulation of backward falls

A critical missing component in the study of real-world falls is the ability to accurately determine impact forces resulting from the fall. Subject-specific rigid body dynamic (RBD) models calibrated to video captured falls can quantify impact forces and provide additional insights into injury risk factors. RBD models were developed based on five backward falls captured on surveillance video in long-term care facilities in British Columbia, Canada. Model joint stiffness and initial velocities were calibrated to match the kinematics of the fall and contact forces were calculated. The effect of joint stiffnesses (neck, lumbar spine, hip, and knee joint) on head contact forces were determined by modifying the calibrated stiffness values ±25%. Fall duration, fall trajectories, and maximum velocities showed a close match between fall events and simulations. The maximum value of pelvic velocity difference between Kinovea (an open-source software 2D digitization software) and Madymo multibody modeling was found to be 6% ± 21.58%. Our results demonstrate that neck and hip stiffness values have a non-significant yet large effect on head contact force (t(3) = 1, p = 0.387 and t(3) = 2, p = 0.138), while lower effects were observed for knee stiffness, and the effect of lumbar spine stiffness was negligible. The subject-specific fall simulations constructed from real world video captured falls allow for direct quantification of force outcomes of falls and may have applications in improving the assessment of fall-induced injury risks and injury prevention methods.

Association Between Hip Bone Mineral Density and Mortality Risk After Hip Fracture: A Prospective Cohort Study

Factors related to mortality after osteoporotic hip fracture (HF) have been investigated intensively, except for proximal femoral bone mineral density (BMD), which is also the primary cause of osteoporosis. In this study, we aimed to investigate the association of hip BMD with mortality risk after HF. Four hundred and eleven elderly patients with HF in Beijing, China, were included and prospectively followed up with a median time of 3 years. At baseline, quantitative CT technique (QCT) was used to measure areal BMD (aBMD) of the unaffected hip. Areal BMDs of the total hip (TH), femoral neck (FN), trochanter (TR), and intertrochanter were analyzed with postoperative mortality as the primary outcome. A total of 394 patients (78.59 ± 7.59 years, 75.4% female) were included in our final analysis, with 86 (82.23 ± 7.00 years, 81.4% female) dead. All hip bone densities demonstrated a significant association with mortality risks in the unadjusted model, but only TR aBMD remained significantly correlated after adjusting for all covariates. Compared to the lower TR aBMD group, the higher TR aBMD group yielded significantly lower death risks (HR 0.21 95% CI 0.05-0.9, P = 0.036). Higher survival probabilities were observed for higher TH and TR aBMD in survival analysis (P < 0.001). Hip BMD, especially TR BMD assessed by QCT, is an independent risk factor for postoperative mortality following HF. QCT may present a promising avenue for opportunistic analysis in immobilized patients, providing valuable information for early detection and personalized interventions to enhance patient outcomes.

A Fracture Risk Assessment Tool for High Resolution Peripheral Quantitative Computed Tomography

Most fracture risk assessment tools use clinical risk factors combined with bone mineral density (BMD) to improve assessment of osteoporosis; however, stratifying fracture risk remains challenging. This study developed a fracture risk assessment tool that uses information about volumetric bone density and three-dimensional structure, obtained using high-resolution peripheral quantitative compute tomography (HR-pQCT), to provide an alternative approach for patient-specific assessment of fracture risk. Using an international prospective cohort of older adults (n = 6802) we developed a tool to predict osteoporotic fracture risk, called μFRAC. The model was constructed using random survival forests, and input predictors included HR-pQCT parameters summarizing BMD and microarchitecture alongside clinical risk factors (sex, age, height, weight, and prior adulthood fracture) and femoral neck areal BMD (FN aBMD). The performance of μFRAC was compared to the Fracture Risk Assessment Tool (FRAX) and a reference model built using FN aBMD and clinical covariates. μFRAC was predictive of osteoporotic fracture (c-index = 0.673, p < 0.001), modestly outperforming FRAX and FN aBMD models (c-index = 0.617 and 0.636, respectively). Removal of FN aBMD and all clinical risk factors, except age, from μFRAC did not significantly impact its performance when estimating 5-year and 10-year fracture risk. The performance of μFRAC improved when only major osteoporotic fractures were considered (c-index = 0.733, p < 0.001). We developed a personalized fracture risk assessment tool based on HR-pQCT that may provide an alternative approach to current clinical methods by leveraging direct measures of bone density and structure. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Geometry and bone mineral density determinants of femoral neck strength changes following exercise

Physical exercise induces spatially heterogeneous adaptation in bone. However, it remains unclear where the changes in BMD and geometry have the greatest impact on femoral neck strength. The aim of this study was to determine the principal BMD-and-geometry changes induced by exercise that have the greatest effect on femoral neck strength. Pre- and post-exercise 3D-DXA images of the proximal femur were collected of male participants from the LIFTMOR-M exercise intervention trial. Meshes with element-by-element correspondence were generated by morphing a template mesh to each bone to calculate changes in BMD and geometry. Finite element (FE) models predicted femoral neck strength changes under single-leg stance and sideways fall load. Partial least squares regression (PLSR) models were developed with BMD-only, geometry-only, and BMD-and-geometry changes to determine the principal modes that explained the greatest variation in neck strength changes. The PLSR models explained over 90% of the strength variation with 3 PLS components using BMD-only (R² > 0.92, RMSE < 0.06 N) and 8 PLS components with geometry-only (R² > 0.93, RMSE < 0.06 N). Changes in the superior neck and distal cortex were most important during single-leg stance while the superior neck, medial head, and lateral trochanter were most important during a sideways fall. Local changes in femoral neck and head geometry could differentiate the exercise groups from the control group. Exercise interventions may target BMD changes in the superior neck, inferior neck, and greater trochanter for improved femoral neck strength in single-leg stance and sideways fall.

The Impact of Coronal Configuration of the Proximal Femur on its Mechanical Properties and the Validation of a New Theoretical Model: Finite Element Analysis and Biomechanical Examination

OBJECTIVE

This study aims to establish the coronal configuration of the proximal femur as an independent factor for its mechanical properties and provide validation for the theoretical model "fulcrum-balance-reconstruction."

METHODS

The digital 3D femur model constructed with the lower extremity high-resolution computed tomography of a senior subject was applied with the axial compression of 2100N under 5 different α angles of 10°, 5°, 0°, -5°, -10°. The equivalent stress distribution of the femoral geometric model under each angle were calculated. Under the same five α angles, fatigue test was performed on 15 composite artificial left femurs (three specimens in each angle group) to obtain the failure cycle and fracture site. The statistical analysis was accomplished using One-Way ANOVA.

RESULTS

The maximum stress of the entire femur in physiological angle (α = 10°) occurred below femoral neck with a value of 63.91 MPa. When the proximal femur is in extreme abducted angle (α = -10°), the maximum stress shift to the lower medial cortex of femoral shaft with a value of 105.2 MPa. As the α angle changed from 10° to -10°, the greater trochanteric region had the largest increment in maximum stress (2.78 times for cortex and 1.67 times for cancellous bone) locally at the proximal femur. The failure cycles of the artificial femurs with a variety of abduction angle were averagely 9126 ± 2453.87 (α = -10°), 58,112.33 ± 1293.84 (α = -5°), 92,879.67 ± 2398.54 (α = 0°), 172,045.3 ± 11011.11 (α = 5°), and 264,949.3 ± 35,067.26 (α = 10°), and the statistical analysis revealed that the α angle of the group of concern is proportional to the P value of the corresponding group compared to the 10° group(α = 5° & α = 10°, P = 0.01; α = 0 & α = 10°, P = 0.001; α = -5°, -10° & α = 10°, P < 0.001). In fatigue test, the fracture appeared on femoral neck for the α angles of 10° (three subcapital), 5° (two basal; one transcervical), and 0° (one transcervical). Fracture sites located at trochanteric region were observed with the more abducted angles including 0° (two subtrochanteric) and -5° (two intertrochanteric; one subtrochanteric). The fracture line was only found on femoral shaft in the -10° group.

CONCLUSION

With increasing hip abduction, the proximal femur shows declining mechanical properties, which suggests higher risk of hip fracture and increasement in the fraction of trochanteric fracture subtype. Furthermore, the hypothesis of "fulcrum-balance-reconstruction" was validated by our study to a certain extent.

Body composition and 6 minute walking ability in late-onset pompe disease patients after 9 years of enzyme replacement therapy

OBJECTIVE

Pompe disease is a rare autosomal recessive disorder caused by the deficiency of acid α-glycosidase resulting in accumulation of glycogen in the lysosomes. The late-onset form of the disease (LOPD) causes primarily progressive muscle weakness and respiratory insufficiency. Enzyme replacement therapy (ERT) introduced in 2006, showed mild improvement or stabilization of the symptoms although long-term data are limited. Aim of the study was to describe the progression of body composition and walking ability in LOPD patients receiving ERT consistently for 9 years.

METHODS

Lean body mass, bone mineral density, body fat and 6 min walking distance were assessed in three male and three female LOPD patients (height 165.8 ± 11.2 cm, age 42.3 ± 11.8yrs, body mass 71.1 ± 20.8 kg, at study entry), every three years, for 9 years since ERT initiation (T0, T3, T6, T9).

RESULTS

Total body and upper extremities' lean mass remained unchanged (p < 0.05), but it was decreased for the lower extremities (T3:13.06 ± 3.848 kg vs. T9:11.63 ± 3.49 kg, p < 0.05). Lean body mass was not significantly different after 9 years of ERT compared to before the ERT initiation (T0 to T9). Bone mineral density remained unchanged. Percent body fat increased (T0:39.1 ± 10.3%, vs. T9:43.1 ± 10.4%, p < 0.05). Six minute walking distance tended to increase after 3 years of ERT and decreased gradually thereafter, with no difference between T0-T9. Lean mass of the lower extremities adjusted for body weight was significantly correlated with 6 min walking distance (r = 0.712, p < 0.05).

CONCLUSION

The current data show that enzyme replacement therapy may preserve lean body mass, bone mineral density and walking capacity in LOPD patients.

Femur geometry and body composition influence femoral neck stresses: A combined fall simulation and beam modelling approach

Metrics of femur geometry and body composition have been linked to clinical hip fracture risk. Mechanistic explanations for these relationships have generally focused on femur strength; however, impact loading also modulates fracture risk. We evaluated the potential effects of femur geometry and body composition on femoral neck stresses during lateral impacts. Fifteen female volunteers completed low-energy sideways falls on to the hip. Additionally, participants completed ultrasound and dual-energy x-ray absorptiometry imaging to characterize trochanteric soft tissue thickness (TSTT) over the hip and six metrics of femur geometry, respectively. Subject-specific beam models were developed and utilized to calculate peak femoral neck stress (σ_Neck), utilizing experimental impact dynamics. Except for femoral neck axis length, all metrics of femur geometry were positively correlated with σ_Neck (all p < 0.05). Larger/more prominent proximal femurs were associated with increased force over the proximal femur, whereas a wider neck-shaft angle was associated with greater stress generation independent of force (all p < 0.05). Body mass index (BMI) and TSTT were negatively correlated with σ_Neck (both p < 0.05). Despite strong correlations, these metrics of body composition appear to influence femoral neck stresses through different mechanisms. Increased TSTT was associated with reduced force over the proximal femur, whereas increased BMI was associated with greater resistance to stress generation (both p < 0.05). This study provided novel insights into the mechanistic pathways through which femur geometry and body composition may modulate hip fracture risk. Our findings complement clinical findings and provide one possible explanation for incongruities in the clinical fracture risk and femur strength literature.

Muscle density is an independent risk factor of second hip fracture: a prospective cohort study

BACKGROUND

Patients with a first hip fracture are at high risk of fracturing their other hip. Despite this, preventive therapy is often not given. Because little is known about specific risk factors of a second hip fracture, we investigated the association with areal bone mineral density (aBMD), muscle size, and density. We also investigated whether muscle parameters predict the risk of a contralateral fracture independently of aBMD.

METHODS

Three groups were included, one without hip fracture (a subcohort of the China Action on Spine and Hip Status study), one with a first, and one with a second hip fracture. Subjects with fractures were recruited from the longitudinal Chinese Second Hip Fracture Evaluation (CSHFE). Computed tomography scans of CSHFE patients, which were obtained immediately following their first fracture, were used to measure cross-sectional area and density of the gluteus maximus (G.MaxM) and gluteus medius and minimus (G.Med/MinM) muscles. Computed tomography X-ray absorptiometry was used to measure aBMD of the contralateral femur. Median follow-up time to second fracture was 4.5 years. Cox proportional hazards models were used to compute hazard ratios (HR) of second hip fracture risk in subjects with a first hip fracture. Multivariate logistic regressions were used to compare odds ratios (OR) for the risk of a first and second hip fracture.

RESULTS

Three hundred and one participants (68.4 ± 6.1 years, 64% female) without and 302 participants (74.6 ± 9.9 years, 71% female) with a first hip fracture were included in the analysis. Among the latter, 45 (79.2 ± 7.1 years) sustained a second hip fracture. ORs for first hip fracture were significant for aBMD and muscle size and density. ORs for a second fracture were smaller by a factor of 3 to 4 and no longer significant for femoral neck (FN) aBMD. HRs for predicting second hip fracture confirmed the results. G.Med/MinM density (HR, 1.68; CI, 1.20-2.35) and intertrochanter aBMD (HR, 1.62; CI, 1.13-2.31) were the most significant. FN aBMD was not significant. G.Med/MinM density remained significant for predicting second hip fracture after adjustment for FN (HR, 1.66; Cl, 1.18-2.30) or total hip aBMD (HR, 1.50; 95% Cl, 1.04-2.15).

CONCLUSIONS

Density of the G.Med/MinM muscle is an aBMD independent predictor of the risk of second hip fracture. Intertrochanteric aBMD is a better predictor of second hip fracture than FN and total hip aBMD. These results may trigger a paradigm shift in the assessment of second hip fracture risk and prevention strategies.

Determinants of fracture type in the proximal femur: Biomechanical study of fresh frozen cadavers and finite element models

BACKGROUND

Proximal femur fractures are usually categorized as either a cervical or trochanteric fracture, but the relationship between fracture type and fall direction is not clear. By cadaveric mechanical testing and finite element analysis (FEA), the aims of this research were to verify the factors that define the proximal femur fracture type and to clarify the change in stress distribution based on fall direction.

METHODS

From fresh frozen cadavers, we obtained 26 proximal femora including ten pairs of 20 femora. We conducted quasi-static compression tests in two fall patterns (lateral and posterolateral), and identified the fracture type. We then examined the relationship between fracture type and the following explanatory variables: age, sex, neck shaft angle, femoral neck length, bone mineral density (cervical and trochanteric), and fall direction. In addition, for the ten pairs of femurs, the effect of fall direction on fracture type was examined by comparing the left and right sides. In addition, we generated the proximal femur finite element (FE) models from computed tomography data to simulate and verify the change of external force in different fall directions.

RESULTS

In mechanical tests, only fall direction was found to have a significant relationship with fracture type (p = 0.0227). The posterolateral fall group had a significantly higher incidence of trochanteric fractures than lateral fall group (p = 0.0325). According to FEA, the equivalent stress in the lateral fall was found to be more concentrated in the cervical area than in the posterolateral fall.

CONCLUSION

In proximal femur fractures, fall direction was significantly associated with fracture type; in particular, trochanteric fractures were more likely to occur following a posterolateral fall than a lateral fall.

Bone Microarchitecture Phenotypes Identified in Older Adults Are Associated With Different Levels of Osteoporotic Fracture Risk

Prevalence of osteoporosis is more than 50% in older adults, yet current clinical methods for diagnosis that rely on areal bone mineral density (aBMD) fail to detect most individuals who have a fragility fracture. Bone fragility can manifest in different forms, and a "one-size-fits-all" approach to diagnosis and management of osteoporosis may not be suitable. High-resolution peripheral quantitative computed tomography (HR-pQCT) provides additive information by capturing information about volumetric density and microarchitecture, but interpretation is challenging because of the complex interactions between the numerous properties measured. In this study, we propose that there are common combinations of bone properties, referred to as phenotypes, that are predisposed to different levels of fracture risk. Using HR-pQCT data from a multinational cohort (n = 5873, 71% female) between 40 and 96 years of age, we employed fuzzy c-means clustering, an unsupervised machine-learning method, to identify phenotypes of bone microarchitecture. Three clusters were identified, and using partial correlation analysis of HR-pQCT parameters, we characterized the clusters as low density, low volume, and healthy bone phenotypes. Most males were associated with the healthy bone phenotype, whereas females were more often associated with the low volume or low density bone phenotypes. Each phenotype had a significantly different cumulative hazard of major osteoporotic fracture (MOF) and of any incident osteoporotic fracture (p < 0.05). After adjustment for covariates (cohort, sex, and age), the low density followed by the low volume phenotype had the highest association with MOF (hazard ratio = 2.96 and 2.35, respectively), and significant associations were maintained when additionally adjusted for femoral neck aBMD (hazard ratio = 1.69 and 1.90, respectively). Further, within each phenotype, different imaging biomarkers of fracture were identified. These findings suggest that osteoporotic fracture risk is associated with bone phenotypes that capture key features of bone deterioration that are not distinguishable by aBMD. © 2021 American Society for Bone and Mineral Research (ASBMR).

Osteoporosis and fractures in women: the burden of disease

Osteoporosis is a disease characterized by impaired bone microarchitecture and reduced bone mineral density (BMD) resulting in bone fragility and increased risk of fracture. In western societies, one in three women and one in five men will sustain an osteoporotic fracture in their remaining lifetime from the age of 50 years. Fragility fractures, especially of the spine and hip, commonly give rise to increased morbidity and mortality. In the five largest European countries and Sweden, fragility fractures were the cause of 2.6 million disability-adjusted life years in 2016 and the fracture-related costs increased from €29.6 billion in 2010 to €37.5 billion in 2017. In the European Union and the USA, only a small proportion of women eligible for pharmacological treatment are being prescribed osteoporosis medication. Secondary fracture prevention, using Fracture Liaison Services, can be used to increase the rates of fracture risk assessment, BMD testing and use of osteoporosis medication in order to reduce fracture numbers. Additionally, established primary prevention strategies, based on case-finding methods utilizing fracture prediction tools, such as FRAX, to identify women without fracture but with elevated risk, are recommended in order to further reduce fracture numbers.

Type 2 Diabetes and Change in Total Hip Bone Area and Bone Mineral Density in Swedish Men and Women Older Than 55 Years

CONTEXT

In a cross-sectional study, we found an association between type 2 diabetes mellitus (T2DM) and smaller bone area together with greater bone mineral density (BMD) at the total hip.

OBJECTIVE

This work aims to investigate these associations longitudinally, by studying T2DM status (no T2DM n = 1521, incident T2DM n = 119, or prevalent T2DM n = 106) in relation to changes in total hip bone area and BMD.

METHODS

In 3 cohorts, the Swedish Mammography Cohort Clinical (SMCC; n = 1060), Prospective Investigation of the Vasculature in Uppsala Seniors (PIVUS; n = 483), and Uppsala Longitudinal Study of Adult Men (ULSAM; n = 203), with repeat assessment of T2DM status and dual energy x-ray absorptiometry (DXA) measurements of total hip bone area and BMD on average 8 years apart, a linear regression model was used to assess the effect of T2DM status on change in bone area and BMD at the total hip.

RESULTS

After meta-analysis, the change in bone area at the total hip was 0.5% lower among those with incident T2DM compared to those without T2DM (-0.18 cm2; 95% CI, -0.30 to -0.06). The change in bone area was similar among those with prevalent T2DM compared to those without (0.00 cm2; 95% CI, -0.13 to 0.13). For BMD, the combined estimate was 0.004 g/cm2 (95% CI, -0.006 to 0.014) among those with incident T2DM and 0.010 g/cm2 (95% CI, -0.000 to 0.020) among those with prevalent T2DM, compared to those without T2DM.

CONCLUSION

Those with incident T2DM have a lower expansion in bone area at the total hip compared to those without T2DM.

The association of osteochemometrics and bone mineral density in humans

OBJECTIVES

Even though much is known about bone mineral and matrix composition, studies about their relationship with several bone properties and its alterations related to bone diseases such as osteoporosis are practically non-existent in humans. Thus, the development of methods to understand the effects of bone properties at a microscopic level is paramount. This research aimed to evaluate whether Fourier transform infrared-attenuated total reflectance (FTIR-ATR) band intensity ratios correlate with femoral bone mass, bone mineral content (BMC) (total and femoral neck), bone mineral per unit area (BMD) (total, femoral neck, greater trochanter, intertrochanteric region, and Ward's area) and the area (total and femoral neck). A sample of femora from the 21st Century Identified Skeleton Collection (N = 78, 42 females and 36 males) was employed and BMC, BMD, and the femoral areas were acquired by DXA.

RESULTS

It was found that only females' BMD had a significant association with the femoral FTIR-ATR indices under study, whereas bone collagen (Am/P) and the content of carbonate Type A (API) in males correlated with the total proximal femur area of the regions of interest and the femoral neck area.

DISCUSSION

Men and women showed different changes related to their chemical composition in BMD, BMC, and probed area, most likely due to differences in structure and physiology, as well as mechanical strength in the proximal femoral sites where BMD was analyzed.

Trabecular and cortical bone involvement in rheumatoid arthritis by DXA and DXA-based 3D modelling

Rheumatoid arthritis (RA) patients had a higher risk of developing low bone mineral density (BMD) or osteoporosis. RA patients on classic disease-modifying antirheumatic drug (c-DMARD) therapy showed significantly lower BMD than controls, while no significant differences in most parameters were found between RA patients receiving biological disease-modifying antirheumatic drugs (b-DMARDs) and controls. The 3D analysis allowed us to find changes in the trabecular and cortical compartments.

INTRODUCTION

To evaluate cortical and trabecular bone involvement of the hip in RA patients by dual-energy X-ray absorptiometry (DXA) and 3D analysis. The secondary end-point was to evaluate bone involvement in patients treated with classic (c-DMARD) or biological (b-DMARD) disease-modifying antirheumatic drug therapies and the effect of the duration of the disease and corticosteroid therapy on 3D parameters.

METHODS

A cross-sectional study of 105 RA patients and 100 subjects as a control group (CG) matched by age, sex, and BMI was carried out. BMD was measured by DXA of the bilateral femoral neck (FN) and total hip (TH). The 3D analyses including trabecular and cortical BMD were performed on hip scans with the 3D-Shaper software.

RESULTS

FN and TH BMD and trabecular and cortical vBMD were significantly lower in RA patients. The c-DMARD (n = 75) group showed significantly lower trabecular and cortical vBMD than the CG. Despite the lower values, the b-DMARD group (n = 30) showed no significant differences in most parameters compared with the CG. The trabecular and cortical 3D parameters were significantly lower in the group with an RA disease duration of 1 to 5 years than in the CG, and the trabecular vBMD was significantly lower in the group with a duration of corticosteroid therapy of 1 to 5 years than in the CG, while no significant differences were found by standard DXA in the same period.

CONCLUSIONS

RA patients had a higher risk of developing low BMD or osteoporosis than controls. RA patients receiving c-DMARD therapy showed significantly lower BMD than controls, while no significant differences in most parameters were found between RA patients receiving b-DMARDs and controls. 3D-DXA allowed us to find changes in trabecular and cortical bone compartments in RA patients.

Assessment of femoral neck strength and bone mineral density changes following exercise using 3D-DXA images

Physical exercise induces spatially heterogeneous bone changes in the proximal femur. Recent advances have enabled 3D dual-energy X-ray Absorptiometry (DXA)-based finite element (FE) models to estimate bone strength. However, its ability to detect exercise-induced BMD and strength changes is unclear. The aim of this study was to quantify the repeatability of vBMD and femoral neck strength obtained from 3D-DXA images and determine the changes due an exercise intervention. The DXA scans included pairs of same-day repeated scans from ten healthy females and pre- and post-exercise intervention scans of 26 males. FE models with element-by-element correspondence were generated by morphing a template mesh to each bone. BMD and femoral strength under single-leg-stance and sideways fall loading configurations were obtained for both groups and compared. In the repeated images, the total hip vBMD difference was 0.5 ± 2.5%. Element-by-element BMD differences reached 30 ± 50%. The strength difference in single-leg stance was 2.8 ± 13% and in sideways fall was 4.5% ± 19%. In the exercise group, strength changes were 6 ± 19% under single-leg stance and 1 ± 18% under sideways fall. vBMD parameters were weakly correlated to strength (R² < 0.31). The exercise group had a mean bone accrual exceeding repeatability values in the femoral head and cortical regions. The case with the highest vBMD change (6.4%) caused 18% and -7% strength changes under single-leg stance and sideways fall. 3D-DXA technology can assess the effect of exercise interventions in large cohorts but its validity in individual cases should be interpreted with caution.

The effect of the hip impact configuration on the energy absorption provided by the femoral soft tissue during sideways falls

The femoral soft tissue (i.e., skin, muscle, fat) may play a key role in preventing hip fractures during a fall by absorbing the impact energy. We measured the femoral soft tissue deformation and associated compressive force during simulated sideways falls to estimate the energy absorbed by the soft tissue, and then examined how this was affected by the hip impact configuration and gender. Eighteen young adults (9 males and 9 females) participated in the pelvis release experiment. The pelvis was raised through a rope attached to an electromagnet on the ceiling, so the skin surface barely touches the ultrasound probe, which flush to a Plexiglas plate placed on a force plate. The electromagnet was turned off to cause a fall while the soft tissue deformation and associated compressive force were being recorded. Trials were acquired with three hip impact configurations. An outcome variable included the energy absorbed by the femoral soft tissue during a fall. The energy absorbed by the femoral soft tissue ranged from 0.03 to 3.05 J. Furthermore, the energy absorption was associated with the hip impact configuration (F = 4.69, p = 0.016). On average, the absorbed energy was 62% greater in posteriolateral than anteriolateral impact (0.92 versus 0.57 J). However, the energy absorption did not differ between male and female (F = 0.91, p = 0.36). The force-deflection behavior of the femoral soft tissue during a fall has been recorded, providing insights on the potential protective benefits of the soft tissue covering during a fall.

Effect of fall characteristics on the severity of hip impact during a fall on the ground from standing height

The magnitude of hip impact force during a fall on the ground (i.e., concrete surface) from standing height was determined. We found that this force decreases up to 59%, depending on how they land on the ground.

INTRODUCTION

We determined the magnitude of hip impact force that humans may experience in the event of a fall from standing height on the ground, in order to examine how the hip impact force was affected by characteristics of a fall.

METHODS

Twenty subjects mimicked a typical older adults' falls on a mat. Trials were acquired with three initial fall directions: forward, sideways, and backward. Trials were also acquired with three knee positions at the time of hip impact: knee together, knee on the mat, and free knee. During falls, attenuated vertical hip impact forces and corresponding depression of the mat were measured via a force plate placed under the mat and motion capture system, respectively. Using a mass-spring model, actual hip impact force and body stiffness during a fall on the ground were estimated.

RESULTS

Hip impact force averaged 4.0 kN (SD = 1.7). The hip impact force was associated with knee condition (F = 25.6, p < 0.005), but not with fall direction (F = 0.4, p = 0.599). Compared with "knee on the mat," hip impact force averaged 59% and 45% greater in "free knee" and "knee together," respectively (4.6 versus 2.9 kN, p < 0.005; 4.3 versus 2.9 kN, p < 0.005). However, the hip impact force did not differ between "free knee" and "knee together (4.6 versus 4.3 kN, p = 0.554).

CONCLUSION

Our results suggest that hip fracture risk during a fall decreases substantially, depending on how they land on the ground, informing the development of safe landing strategies to prevent fall-related hip fractures in older adults.

Sub-trabecular strain evolution in human trabecular bone

To comprehend the most detrimental characteristics behind bone fractures, it is key to understand the material and tissue level strain limits and their relation to failure sites. The aim of this study was to investigate the three-dimensional strain distribution and its evolution during loading at the sub-trabecular level in trabecular bone tissue. Human cadaver trabecular bone samples were compressed in situ until failure, while imaging with high-resolution synchrotron radiation X-ray tomography. Digital volume correlation was used to determine the strains inside the trabeculae. Regions without emerging damage were compared to those about to crack. Local strains in close vicinity of developing cracks were higher than previously reported for a whole trabecular structure and similar to those reported for single isolated trabeculae. Early literature on bone fracture strain thresholds at the tissue level seem to underestimate the maximum strain magnitudes in trabecular bone. Furthermore, we found lower strain levels and a reduced ability to capture detailed crack-paths with increased image voxel size. This highlights the dependence between the observed strain levels and the voxel size and that high-resolution is needed to investigate behavior of individual trabeculae. Furthermore, low trabecular thickness appears to be one predictor of developing cracks. In summary, this study investigated the local strains in whole trabecular structure at sub-trabecular resolution in human bone and confirmed the high strain magnitudes reported for single trabeculae under loading and, importantly extends its translation to the whole trabecular structure.

Exercise and Peak Bone Mass

PURPOSE OF REVIEW

The main goal of this narrative review is to assess whether physical activity (PA) influences peak bone mass and fracture risk.

RECENT FINDINGS

Several randomized controlled trials (RCT) show that short-term PA intervention programs in childhood improve the accrual of bone mineral. There are now also long-term controlled PA intervention studies demonstrating that both boys and girls with daily school PA through puberty gain higher bone mineral content (BMC) and bone mineral density (BMD) and greater bone size than boys and girls with school PA 1-2 times/week. These benefits seem to be followed by a gradual reduction in expected fracture rates, so that in children with daily school PA, the incidence rate ratio (IRR) after 8 years is less than half that expected by age. Daily school PA from before to after puberty is associated with beneficial gains in bone traits and gradually lower relative fracture risk.

Hip fracture risk functions for elderly men and women in sideways falls

Falls among the elderly cause a huge number of hip fractures world-wide. The objective is to generate hip fracture force risk functions for elderly women and men in sideways falls which can be used for determining effectiveness of fall prevention measures as well as for individual assessment of fracture risk at the clinics. A literature survey was performed and ten publications were identified who contained several hundred individual femoral neck fracture forces in sideways fall for both elderly women and men. Theoretical distributions were tested for goodness of fit against the pooled dataset with the Anderson-Darling test (AD-test) and root mean square errors (RMSE) were extracted. According to the AD-test, a Weibull distribution is a plausible model for the distribution of hip fracture forces. A simple, exponential two-parameter Weibull function was therefore proposed, having a RMSE below 2.2% compared to the experimental distribution for both men and women. It was demonstrated that elderly women only can endure nearly half the proximal femur force for 5 and 10% fracture risk as elderly men. It should be noted though, that women were found to have significantly lesser body height and body weight which would produce less impact force during falls from standing height. The proposed sex-specific hip fracture risk functions can be used for biomechanically optimizing hip protectors and safety floors and for determining their effectiveness as a fall prevention measure.

Proximal femur lag screw placement based on bone mineral density determined by quantitative computed tomography

Following internal fixations for intertrochanteric fractures in elderly patients, lag screws or screw blades frequently cut the femoral head, leading to surgical failure. The bone mineral density (BMD) at various parts of the proximal femur is significantly correlated with the holding force of the lag screw, which in turn is closely associated with the stability of the fixation. However, the appropriate placement of the lag screw has been controversial. As a novel detection method for BMD, quantitative computed tomography (QCT) may provide relatively accurate measurements of three-dimensional structures and may provide an easy way to determine the appropriate lag screw placement. A total of 50 elderly patients with intertrochanteric fractures were selected for the present study. The BMD of the proximal femur on the healthy side, including the femoral intertrochanter, neck and head, was measured using QCT. For testing, the femoral head was divided into medial, central and lateral sections. The BMD of the femoral head was determined to be the highest, while the BMD of the femoral neck was the lowest. In the femoral head, the central section had the highest BMD, while the lateral section had the lowest BMD. The present study used QCT to detect differences in the BMD at various regions of the proximal femur and provided a novel theoretical reference for the placement of lag screws. To obtain maximum holding power, the lag screw must be placed in the central section of the femoral head.

Perspectives on the non-invasive evaluation of femoral strength in the assessment of hip fracture risk

We reviewed the experimental and clinical evidence that hip bone strength estimated by BMD and/or finite element analysis (FEA) reflects the actual strength of the proximal femur and is associated with hip fracture risk and its changes upon treatment.

INTRODUCTION

The risk of hip fractures increases exponentially with age due to a progressive loss of bone mass, deterioration of bone structure, and increased incidence of falls. Areal bone mineral density (aBMD), measured by dual-energy X-ray absorptiometry (DXA), is the most used surrogate marker of bone strength. However, age-related declines in bone strength exceed those of aBMD, and the majority of fractures occur in those who are not identified as osteoporotic by BMD testing. With hip fracture incidence increasing worldwide, the development of accurate methods to estimate bone strength in vivo would be very useful to predict the risk of hip fracture and to monitor the effects of osteoporosis therapies.

METHODS

We reviewed experimental and clinical evidence regarding the association between aBMD and/orCT-finite element analysis (FEA) estimated femoral strength and hip fracture risk as well as their changes with treatment.

RESULTS

Femoral aBMD and bone strength estimates by CT-FEA explain a large proportion of femoral strength ex vivo and predict hip fracture risk in vivo. Changes in femoral aBMD are strongly associated with anti-fracture efficacy of osteoporosis treatments, though comparable data for FEA are currently not available.

CONCLUSIONS

Hip aBMD and estimated femoral strength are good predictors of fracture risk and could potentially be used as surrogate endpoints for fracture in clinical trials. Further improvements of FEA may be achieved by incorporating trabecular orientations, enhanced cortical modeling, effects of aging on bone tissue ductility, and multiple sideway fall loading conditions.

Enhancing hip fracture risk prediction by statistical modeling and texture analysis on DXA images

Each year in the US more than 300,000 older adults suffer from hip fractures. While protective measures exist, identification of those at greatest risk by DXA scanning has proved inadequate. This study proposed a new technique to enhance hip fracture risk prediction by accounting for many contributing factors to the strength of the proximal femur. Twenty-two isolated cadaveric femurs were DXA scanned, 16 of which had been mechanically tested to failure. A function consisting of the calculated modes from the statistical shape and appearance modeling (to consider the shape and BMD distribution), homogeneity index (representing trabecular quality), BMD, age and sex of the donor was created in a training set and used to predict the fracture load in a test group. To classify patients as "high risk" or "low risk", fracture load thresholds were investigated. Hip fracture load estimation was significantly enhanced using the new technique in comparison to using t-score or BMD alone (average R² of 0.68, 0.32, and 0.50, respectively) (P < 0.05). Using a fracture cut-off of 3400 N correctly predicted risk in 94% of specimens, a substantial improvement over t-score classification (38%). Ultimately, by identifying patients at high risk more accurately, devastating hip fractures can be prevented through applying protective measures.

Predicting bone strength from CT data: Clinical applications

In this review we summarise over 15 years of research and development around the prediction of whole bones strength from Computed Tomography data, with particular reference to the prediction of the risk of hip fracture in osteoporotic patients. We briefly discuss the theoretical background, and then provide a summary of the laboratory and clinical validation of these modelling technologies. We then discuss the three current clinical applications: in clinical research, in clinical trials, and in clinical practice. On average the strength predicted with finite element models (QCT-FE) based on computed tomography is 7% more accurate that that predicted with areal bone mineral density from Dual X-ray Absorptiometry (DXA-aBMD), the current standard of care, both in term of laboratory validation on cadaver bones and in terms of stratification accuracy on clinical cohorts of fractured and non-fractured women. This improved accuracy makes QCT-FE superior to DXA-aBMD in clinical research and in clinical trials, where the its use can cut in half the number of patients to be enrolled to get the same statistical power. For routine clinical use to decide who to treat with antiresorptive drugs, QCT-FE is more accurate but less cost-effective than DXA-aBMD, at least when the decision is on first line treatment like bisphosphonates. But the ability to predict skeletal strength from medical imaging is now opening a number of other applications, for example in paediatrics and oncology.

Algorithm for the Use of Biochemical Markers of Bone Turnover in the Diagnosis, Assessment and Follow-Up of Treatment for Osteoporosis

Introduction

Increased biochemical bone turnover markers (BTMs) measured in serum are associated with bone loss, increased fracture risk and poor treatment adherence, but their role in clinical practice is presently unclear. The aim of this consensus group report is to provide guidance to clinicians on how to use BTMs in patient evaluation in postmenopausal osteoporosis, in fracture risk prediction and in the monitoring of treatment efficacy and adherence to osteoporosis medication.

Methods

A working group with clinical scientists and osteoporosis specialists was invited by the Scientific Advisory Board of European Society on Clinical and Economic Aspects of Osteoporosis, Osteoarthritis and Musculoskeletal Diseases (ESCEO).

Results

Serum bone formation marker PINP and resorption marker βCTX-I are the preferred markers for evaluating bone turnover in the clinical setting due to their specificity to bone, performance in clinical studies, wide use and relatively low analytical variability. BTMs cannot be used to diagnose osteoporosis because of low sensitivity and specificity, but can be of value in patient evaluation where high values may indicate the need to investigate some causes of secondary osteoporosis. Assessing serum levels of βCTX-I and PINP can improve fracture prediction slightly, with a gradient of risk of about 1.2 per SD increase in the bone marker in addition to clinical risk factors and bone mineral density. For an individual patient, BTMs are not useful in projecting bone loss or treatment efficacy, but it is recommended that serum PINP and βCTX-I be used to monitor adherence to oral bisphosphonate treatment. Suppression of the BTMs greater than the least significant change or to levels in the lower half of the reference interval in young and healthy premenopausal women is closely related to treatment adherence.

Conclusion

In conclusion, the currently available evidence indicates that the principal clinical utility of BTMs is for monitoring oral bisphosphonate therapy.

Does peak bone mass correlate with peak bone strength? Cross-sectional normative dual energy X-ray absorptiometry data in 1052 men aged 18-28 years

Background

Areal bone mineral density (aBMD) estimated by dual-energy X-ray absorptiometry (DXA) is used to estimate peak bone mass, define osteoporosis and predict fracture. However, as aBMD is calculated as bone mineral content (BMC) divided by the scanned area, aBMD displays an inverse relationship with bone size. In a skeleton that is increasing in size, this is a problem, as bone size is an independent factor that determines bone strength. It could therefore be questioned whether peak aBMD is the period with greatest bone strength, a period that in the hip then would occur in ages 16–19. The aim of this study was to evaluate whether there are changes in bone size in men after age 18 that may influence peak bone strength. Another aim was to provide updated normative DXA data.

Methods

We scanned left femoral neck by DXA in a cross-sectional study with a population-based selection of 1052 men aged 18–28, and then registered bone mineral content (BMC, gram), aBMD (gram/cm²) and bone area (cm²) in each one-year age group. We performed analyses of variance (ANOVA) to evaluate whether there were differences in these traits between the age groups. We then used Pearson’s correlation analyses to test for trends with ageing after peak bone mass was reached.

Results

We found the highest absolute femoral neck aBMD at age 19, with statistically significant differences between the one-year age groups in BMC, aBMD, and bone area (all p < 0.05). From peak bone mass onwards (n = 962), there are negative correlations between age and BMC (r = − 0.07; p < 0.05) and age and aBMD (r = − 0.12; p < 0.001), and positive correlation between age and bone area (r = 0.06; p < 0.05).

Conclusion

As femoral neck bone size in young adult men becomes larger after peak bone mass, it could be questioned whether DXA estimated peak aBMD correlates with peak bone strength. We infer that aBMD must be interpreted with care in individuals with a growing skeleton, since skeletal strength may then increase, in spite of decreasing aBMD. This should be taken into account when performing DXA measurements in these ages.

Subject-specific ex vivo simulations for hip fracture risk assessment in sideways falls

The risk of hip fracture of a patient due to a fall can be described from a mechanical perspective as the capacity of the femur to withstand the force that it experiences in the event of a fall. So far, impact forces acting on the lateral aspect of the pelvic region and femur strength have been investigated separately. This study used inertia-driven cadaveric impact experiments that mimic falls to the side from standing in order to evaluate the subject-specific force applied to the hip during impact and the fracture outcome in the same experimental model. Eleven fresh-frozen pelvis-femur constructs (6 female, 5 male, age = 77 years (SD = 13 years), BMI = 22.8 kg/m² (SD = 7.8 kg/m²), total hip aBMD = 0.734 g/cm² (SD = 0.149 g/cm²)), were embedded into soft tissue surrogate material that matched subject-specific mass and body shape. The specimens were attached to metallic lower-limb constructions with subject-specific masses and subjected to an inverted pendulum motion. Impact forces were recorded with a 6-axis force plate at 10,000 Hz and three dimensional deflections in the pelvic region were tracked with two high-speed cameras at 5000 Hz. Of the 11 specimens, 5 femur fractures and 3 pelvis fractures were observed. Three specimens did not fracture. aBMD alone did not reliably separate femur fractures from non-fractures. However, a mechanical risk ratio, which was calculated as the impact force divided by aBMD, classified specimens reliably into femur fractures and non-fractures. Single degree of freedom models, based on specimen kinetics, were able to predict subject-specific peak impact forces (RMSE = 2.55% for non-fractures). This study provides direct evidence relating subject-specific impact forces and subject-specific strength estimates and improves the assessment of the mechanical risk of hip fracture for a specific femur/pelvis combination in a sideways fall.

Force, impulse and energy during falling with and without knee protection: an in-vitro study

The mechanics of protective knee padding mitigating injury from a high-force fall have not been investigated in real-life scenarios to date. This study compares the effect of wearing knee pads to unprotected impact on a hard surface. We hypothesized that knee pads reduce the force and energy transmitted to the bony structures of the knee cap compared with unprotected conditions. Eight human knee cadaver specimens were embedded and fixed with a flexion angle of 100 degrees in a custom-made drop testing device (75 kg including the knee). The usage of a knee pad led to an average peak force attenuation on impact of 15% (no pad: 5932 N SD: 2472 N; pad: 4210 N SD: 2199 N; p < 0.001). Contact time on the plate was higher with a knee pad (no pad: 0.015 s SD: 0.009 s; pad: 0.028 s SD: 0.014 s; p < 0.001). Therefore, the observed impulse was also increased (no pad: 62.2 Ns SD: 17.8 Ns; pad: 74.6 Ns SD: 18.6 Ns; p < 0.001). This effect diminished as drop height was increased. Energy dissipation, defined as the difference between kinetic energy pre-impact and peak potential energy post-impact, was higher without a knee pad (no pad: 10.5 J SD: 6.2 J; pad: 4.2 J SD: 5.0 J; p < 0.001). The results from this study illustrate the magnitude of influence that knee pads have on peak forces, transmitted impulse, and energy transfer from a high-force impact in real-life scenarios. Contrary to expectations, the knee pad did not act as a mechanical damper. The mechanical behavior more closely resembled a spring that temporarily stores energy and consequentially reduces peak forces upon impact. Based on this study, future developments in padding might benefit from focusing on the aspect of energy storage and temporarily delayed energy dissipation.

Definition of a Novel Proximal Femur Classification in the Sagittal Plane According to the Femur Morphometric Analysis

BACKGROUND

Studies on prosthesis positioning and implant design in total hip arthroplasty (THA) have generally focused on the anatomy of the proximal femur in the coronal plane. The aim of this study was to investigate the proximal femur morphology in the sagittal plane to provide better positioning of the femoral component in THA and contribute to the determination of proximal femur morphology through possible outcomes that can be shown also by considering the sagittal plane in the selection and design of the femoral component.

METHODS

Computerized tomography scans were obtained from 270 femoral bones belonging to adult skeletons, followed by 3D reconstruction using Leonardo Dr/Dsa Va30a software (Siemens, Erlangen, Germany) and measurements. Canal widths were measured in the coronal and sagittal planes at the lesser trochanter (LT) level, at 20 millimeters proximal to the LT(LT+20) and at various levels distal to the lesser trochanter in 25 mm jumps up to 200 mm from the lesser trochanter.

RESULTS

The average width was wider at the level of the lesser trochanter and all points distal to it in the sagittal plane compared to the coronal plane except LT-200 mm. At each levels from LT-25 to LT-175, the differences were statistically significant (P < .05). The ratio of the femoral width at the lesser trochanter level to the width 50 mm distal to the LT was stated as the most prevalent one, and a novel classification in the sagittal plane was developed in accordance with these findings.

CONCLUSION

A novel and simple classification in the sagittal plane was developed based on the findings of this study, and this classification may improve the accuracy, validity, and reliability of femoral stem fixation in total hip arthroplasty.

A novel method for estimating nail-tract bone density for intertrochanteric fractures

SUMMARY

A novel method based on voxel-based morphometry was proposed to investigate the average volumetric bone mineral density (vBMD) of femoral head nail tract in patients treated with intramedullary nails-proximal femoral nail antirotation (PFNA) and gamma nail (GN). The results showed that there was no significant difference in average vBMD between the two groups.

BACKGROUND

For unstable intertrochanteric fractures, poor bone quality might be one of the most important causes of cut-out complications in the femoral head during surgical treatment. Bone quality is generally regarded as an equivalent of BMD. Thus, we develop a novel voxel-based morphometry-based method to quantify vBMD of the femoral head nail tract.

METHODS

Automatic calculation of average vBMD of nail tracts requires three main steps. First, we built a standard nail tract in a proximal femur template. Then, we mapped the proximal femur structure of each patient to the template by B-spline and Demons registration so that the anatomical positions of the proximal femur of all patients spatially corresponded to the standard template. Finally, we calculated and visualized the average vBMD distribution of the nail tract of all patients. To verify the feasibility of the method, we enrolled 75 patients (52 women and 23 men) with hip fractures to our study to compare measurements. The root mean square of the standard deviation (RMSSD) was calculated, and the coefficient of variation (CV) of the RMSSD (CV-RMSSD) was used to evaluate the reproducibility of intraoperator and interscan measurements. The Mann-Whitney U test was used to compare the average vBMD of nail tracts for the PFNA and GN.

RESULTS

The CV-RMSSD of intraoperator measurements ranged from 1.0% to 2.0%, and the CV-RMSSD of interscan measurements ranged from 3.6% to 4.5%. There was no significant difference in the average vBMD between patients with PFNAs and those with GNs (p > 0.05).

CONCLUSIONS

The proposed method is reproducible for determining the average vBMD, which may provide a reference index for selection of appropriate intramedullary nails for individual patients. The current choice of intramedullary nail based on the experience of a surgeon may be biased.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

A novel method was proposed to measure the spatial average vBMD of nail tracts, which has good potential to provide a reference index for surgeons to choose appropriate implants.

Assessment of finite element models for prediction of osteoporotic fracture

With increasing life expectancy and mortality rates, the burden of osteoporotic hip fractures is continually on an upward trend. In terms of prevention, there are several osteoporosis treatment strategies such as anti-resorptive drug treatments, which attempt to retard the rate of bone resorption, while promoting the rate of formation. With respect to prediction, several studies have provided insights into obtaining bone strength by non-invasive means through the application of FE analysis. However, what valuable information can we obtain from FE studies that have focused on osteoporosis research, with respect to the prediction of osteoporotic fractures? This paper aims to fine studies that have used FE analysis to predict fractures in the proximal femur through a systematic search of literature using PUBMED, with the main objective of supporting the diagnosis of osteoporosis. The focus of these FE studies is first discussed, and the methodological aspects are summarized, by mainly comparing and contrasting their meshing properties, material properties, and boundary conditions. The implications of these methodological differences in FE modelling processes and propositions with the aim of consolidating or minimalizing these differences are further discussed. We proved that studies need to start converging in terms of their input parameters to make the FE method applicable to clinical settings. This, in turn, will decrease the time needed for in vitro tests. Current advancements in FE analysis need to be consolidated before any further steps can be taken to implement engineering analysis into the clinical scenario.

Comparison of Indian Council for Medical Research and Lunar Databases for Categorization of Male Bone Mineral Density

The mainstay of diagnosis of osteoporosis is dual-energy X-ray absorptiometry (DXA) scan measuring areal bone mineral density (BMD) (g/cm²). The aim of the present study was to compare the Indian Council of Medical Research database (ICMRD) and the Lunar ethnic reference database of DXA scans in the diagnosis of osteoporosis in male patients. In this retrospective study, all male patients who underwent a DXA scan were included. The areal BMD (g/cm²) was measured at either the lumbar spine (L1-L4) or the total hip using the Lunar DXA machine (software version 8.50) manufactured by GE Medical Systems (Shanghai, China). The Indian Council of Medical Research published a reference data for BMD in the Indian population derived from the population-based study conducted in healthy Indian individuals, which was used to analyze the BMD result by Lunar DXA scan. The 2 results were compared for various values using statistical software SPSS for Windows (version 16; SPSS Inc., Chicago, IL). A total 238 male patients with a mean age of 57.2 yr (standard deviation ±15.9) were included. Overall, 26.4% (66/250) and 2.8% (7/250) of the subjects were classified in the osteoporosis group according to the Lunar database and the ICMRD, respectively. Out of the 250 sites of the DXA scan, 28.8% (19/66) and 60.0% (40/66) of the cases classified as osteoporosis by the Lunar database were reclassified as normal and osteopenia by ICMRD, respectively. In conclusion, the Indian Council of Medical Research data underestimated the degree of osteoporosis in male subjects that might result in deferring of treatment. In view of the discrepancy, the decision on the treatment of osteoporosis should be based on the multiple fracture risk factors and less reliably on the BMD T-score.

Bone Health During the Menopause Transition and Beyond

The menopause transition is a critical period for bone health, with rapid losses in bone mass and strength occurring in a 3-year window bracketing the date of the final menstrual period. Declines in bone mass are accompanied by deleterious changes in bone macrostructure and microarchitecture, which may be captured by changes in composite strength indices and indices of trabecular thickness and connectivity. The onset of the rapid bone loss phase is preceded by changes in sex steroid hormones and increases in markers of bone resorption, measurements of which may be clinically useful in predicting the onset of the rapid loss phase and in identifying the women who will lose the most bone strength over the menopause transition.

Individualized evaluation of lumbar bone mineral density in children with cerebral palsy

Lumbar spine bone mineral density (LS-BMD) assessed by dual-energy X-ray absorptiometry (DXA) is used in children with cerebral palsy (CP) to evaluate bone health. LS-BMD results in children with CP are influenced significantly by their height, BMI, and mobility level. An adjustment for these parameters might improve the clinical significance of the method.

PURPOSE/INTRODUCTION

DXA evaluation is considered useful in children with CP to assess bone health. For this purpose, LS-BMD is often used. The aim of the study was to estimate the effect of height, BMI, and reduced mobility level of children with CP on LS-BMD and to develop a method to adjust individual results of LS-BMD for these factors.

METHODS

We conducted a monocentric retrospective analysis of data collected in children and adolescents with CP, who participated in a rehabilitation program and had no history of recurrent fractures. The DXA scan was part of the routine examination for participants older than 4 years of age. The relationship between height and BMI for age Z-scores and age-adjusted LS-BMD Z-scores was analyzed.

RESULTS

LS-DXA scans of 500 children and adolescents with CP (Gross Motor Function Classification System levels I-V) were included in the statistical analysis (217 female). The mean age was 9.4 years (± 3.7 years). Children with moderate to severe CP had significantly (p < 0.001) lower LS-BMD Z-scores than children with mild CP. We provided nomograms to adjust individual LS-BMD results to their height, BMI, and mobility level.

CONCLUSIONS

LS-BMD results in children with CP were influenced significantly by their height, BMI, and mobility level. An adjustment of the LS-BMD results to height, BMI, and mobility level might improve the clinical significance of an individual result.

Type 2 Diabetes in Relation to Hip Bone Density, Area, and Bone Turnover in Swedish Men and Women: A Cross-Sectional Study

Men and women with type 2 diabetes mellitus (T2DM) have higher risk of hip fracture, but the mechanisms are not fully understood. We aimed to investigate how T2DM, glucose, and insulin were associated with femoral bone mineral density (BMD), bone mineral area (BMA), and bone turnover markers. We used two cross-sectional cohorts: the Uppsala Longitudinal Study of Adult Men (ULSAM, n = 452, mean age 82 years) and the Swedish Mammography Cohort Clinical (SMCC, n = 4713, mean age 68 years). We identified men and women with normal fasting glucose (NFG), impaired fasting plasma glucose (IFG), and T2DM. BMD and BMA at the total hip and femoral shaft were measured using dual energy X-ray absorptiometry (DXA). Bone turnover markers; CrossLaps and osteocalcin were measured in women. Linear regression models were applied. Men and women showed a progressively higher BMD following the clinical cutoffs of fasting glucose from NFG to IFG to T2DM. In contrast, there was a progressively lower BMA. Men and women with T2DM, compared to those with NFG, had lower BMA at the total hip (- 1.7%; 95% CI - 3.2, - 0.2 and - 1.0%; 95% CI - 1.6, - 0.4) and the femoral shaft (- 2.0%; 95% CI - 3.5, - 0.4 and - 0.6%; 95% CI - 1.2, - 0.01), respectively. T2DM was associated with lower concentrations of CrossLaps (- 8.1%; 95% CI - 12.7, - 3.6) and osteocalcin (- 15.2%; 95% CI - 19.0, - 11.2). These cross-sectional results indicate that those with T2DM have smaller bone area and lower bone turnover, which could increase the risk of hip fracture.

Factors associated with proximal femur fracture determined in a large cadaveric cohort

Many researchers have used cadaveric fracture tests to determine the relationship between proximal femur (hip) fracture strength and a multitude of possible explanatory variables, typically considered one or two at a time. These variables include subject-specific proximal femur variables such as femoral neck areal bone mineral density (aBMD), sex, age, and geometry, as well as physiological hip fracture event variables such as fall speed and angle of impact. However, to our knowledge, no study has included all of these variables simultaneously in the same experimental dataset. To address this gap, the present study simultaneously included all of these subject-specific and fracture event variables in multivariate models to understand their contributions to femoral strength and fracture type. The primary aim of this study was to determine not only whether each of these variables contributed to the prediction of femoral strength, but also to determine the relative importance of each variable in strength prediction. A secondary aim was to similarly characterize the importance of these variables for the prediction of fracture type. To accomplish these aims, we characterized 197 proximal femurs (covering a wide range of subject-specific variables) with DXA and CT scans, and then tested the femurs to fracture in a sideways fall on the hip configuration. Each femur was tested using one of three fall speed conditions and one of four angles of impact (bone orientations). During each test, we acquired measurements of relevant force and displacement data. We then reduced the test data to determine femoral strength, and we used post-fracture CT scans to classify the fracture type (e.g., trochanteric, cervical). Using these results, the explanatory variables were analyzed with mixed statistical models to explain variations in hip fracture strength and fracture type, respectively. Five explanatory variables were statistically significant in explaining the variability in femoral strength: aBMD, sex, age, fall speed, and neck-shaft angle (P ≤ 0.0135). These five variables, including significant interactions, explained 80% of the variability in hip fracture strength. Additionally, when only aBMD, sex, and age (P < 0.0001) were considered in the model, again including significant interactions, these three variables alone explained 79% of the variability in hip fracture strength. So while fall speed (P = 0.0135) and neck-shaft angle (P = 0.0041) were statistically significant, the inclusion of these variables did not appreciably improve the prediction of hip fracture strength compared to the model that considered only aBMD, sex and age. For the variables we included in this study, in the ranges we considered, our findings indicate that the clinically-available information of patient age, sex and aBMD are sufficient for femoral strength assessment. These findings also suggest that there is little value in the extra effort required to characterize the effect of femoral geometry on strength, or to account for the probabilistic nature of fall-related factors such as fall speed and angle of impact. For fracture type, the only explanatory variable found to be significant was aBMD (P ≤ 0.0099). We found that the odds of having intertrochanteric fractures increased by 47% when aBMD decreased by one standard deviation (0.2 g/cm2).

Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip

While metrics of pelvis and femur geometry have been demonstrated to influence hip fracture risk, attempts at linking geometry to underlying mechanisms have focused on fracture strength. We investigated the potential effects of femur and pelvis geometry on applied loads during lateral falls on the hip. Fifteen female volunteers underwent DXA imaging to characterize two pelvis and six femur geometric features. Additionally, participants completed low-energy sideways falls on the hip; peak impact force and pressure, contact area, and moment of force applied to the proximal femur were extracted. No geometric feature was significantly associated with peak impact force. Peak moment of force was significantly associated with femur moment arm (p = 0.005). Peak pressure was positively correlated with pelvis width and femur moment arm (p < 0.05), while contact area was negatively correlated with metrics of pelvis width and femur neck length (p < 0.05). This is the first study to link experimental measures of impact loads during sideways falls with image-based skeletal geometry from human volunteers. The results suggest that while skeletal geometry has limited effects on overall peak impact force during sideways falls, it does influence how impact loads are distributed at the skin surface, in addition to the bending moment applied to the proximal femur. These findings have implications for the design of protective interventions (e.g. wearable hip protectors), and for models of fall-related lateral impacts that could incorporate the relationships between skeletal geometry, external load magnitude/distribution, and tissue-level femur loads.

Structural Parameters of the Proximal Femur by 3-Dimensional Dual-Energy X-ray Absorptiometry Software: Comparison With Quantitative Computed Tomography

Structural parameters of the proximal femur evaluate the strength of the bone and its susceptibility to fracture. These parameters are computed from dual-energy X-ray absorptiometry (DXA) or from quantitative computed tomography (QCT). The 3-dimensional (3D)-DXA software solution provides 3D models of the proximal femur shape and bone density from anteroposterior DXA scans. In this paper, we present and evaluate a new approach to compute structural parameters using 3D-DXA software. A cohort of 60 study subjects (60.9 ± 14.7 yr) with DXA and QCT examinations was collected. 3D femoral models obtained by QCT and 3D-DXA software were aligned using rigid registration techniques for comparison purposes. Geometric, cross-sectional, and volumetric structural parameters were computed at the narrow neck, intertrochanteric, and lower shaft regions for both QCT and 3D-DXA models. The accuracy of 3D-DXA structural parameters was evaluated in comparison with QCT. Correlation coefficients (r) between geometric parameters computed by QCT and 3D-DXA software were 0.86 for the femoral neck axis length and 0.71 for the femoral neck shaft angle. Correlation coefficients ranged from 0.86 to 0.96 for the cross-sectional parameters and from 0.84 to 0.97 for the volumetric structural parameters. Our study demonstrated that accurate estimates of structural parameters for the femur can be obtained from 3D-DXA models. This provides clinicians with 3D indexes related to the femoral strength from routine anteroposterior DXA scans, which could potentially improve osteoporosis management and fracture prevention.

Rate and age-dependent damage elasticity formulation for efficient hip fracture simulations

Prediction of bone failure is beneficial in a range of clinical situations from screening of osteoporotic patients with high fracture risk to assessment of protective equipment against trauma. Computational efficiency is an important feature to consider when developing failure models for iterative applications, such as patient-specific diagnosis or design of orthopaedic devices. The authors previously developed a methodology to generate efficient mesoscale structural full bone models. The aim of this study was to implement a damage elasticity formulation representative of an elasto-plastic material model with age and strain rate dependencies compatible with these structural models. This material model was assessed in the prediction of femoral fractures in longitudinal compression and side fall scenarios. The simulations predicted failure loads and fracture patterns in good agreement with reported results from experimental studies. The observed influence of strain rate on failure load was consistent with literature. The superiority of a simplified elasto-plastic formulation over an elasto-brittle bone material model was assessed. This computationally efficient damage elasticity formulation was capable of capturing fracture development after onset.