Prediction of the strength of the elderly proximal femur by bone mineral density and quantitative ultrasound measurements of the heel and tibia

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.

Magnetic resonance imaging based finite element modelling of the proximal femur: a short-term in vivo precision study

Proximal femoral fractures are a serious life-threatening injury with high morbidity and mortality. Magnetic resonance (MR) imaging has potential to non-invasively assess proximal femoral bone strength in vivo through usage of finite element (FE) modelling (a technique referred to as MR-FE). To precisely assess bone strength, knowledge of measurement error associated with different MR-FE outcomes is needed. The objective of this study was to characterize the short-term in vivo precision errors of MR-FE outcomes (e.g., stress, strain, failure loads) of the proximal femur for fall and stance loading configurations using 13 participants (5 males and 8 females; median age: 27 years, range: 21-68), each scanned 3 times. MR-FE models were generated, and mean von Mises stress and strain as well as principal stress and strain were calculated for 3 regions of interest. Similarly, we calculated the failure loads to cause 5% of contiguous elements to fail according to the von Mises yield, Brittle Coulomb-Mohr, normal principal, and Hoffman stress and strain criteria. Precision (root-mean squared coefficient of variation) of the MR-FE outcomes ranged from 3.3% to 11.8% for stress and strain-based mechanical outcomes, and 5.8% to 9.0% for failure loads. These results provide evidence that MR-FE outcomes are a promising non-invasive technique for monitoring femoral strength in vivo.

Biomechanical analysis of different THA cementless femoral stem designs in physiological and osteoporotic bone during static loading conditions

BACKGROUND

The influence of THA stem design on periprosthetic femoral fractures (PFFs) risk is subject of debate. This study aims to compare the effects of different cementless stem designs on stress-strain distributions in both physiological and osteoporotic femur under various loading conditions.

MATERIALS

A biomechanical study using finite-element analysis was conducted. Four models were developed: three with implanted femurs and a native one chosen as control. Each model was analyzed for both healthy and osteoporotic bone. The following stem designs were examined: short anatomical stem with femoral neck preservation, double-wedge stem, and anatomical standard stem. Three loading conditions were assessed: gait, sideways falling, and four-point bending.

RESULTS

During gait in physiological bone, the anatomical stem and the short anatomical stem with femoral neck preservation showed stress distribution similar to the native model. The double-wedge stem reduced stress in the proximal area but concentrated it in the meta-diaphysis. In osteoporotic bone, the double-wedge stem design increased average stress by up to 10%. During sideways falling, the double-wedge stem exhibited higher stresses in osteoporotic bone. No significant differences in average stress were found in any of the studied models during four-point bending.

CONCLUSION

In physiological bone, anatomical stems demonstrated stress distribution comparable to the native model. The double-wedge stem showed uneven stress distribution, which may contribute to long-term stress shielding. In the case of osteoporotic bone, the double-wedge stem design resulted in a significant increase in average stress during both gait and sideways falling, potentially indicating a higher theoretical risk of PFF.

In Vivo Assessment of Bone Quality Without X-rays

PURPOSE OF REVIEW

This review summarizes recent advances in the assessment of bone quality using non-X-ray techniques.

RECENT FINDINGS

Quantitative ultrasound (QUS) provides multiple measurements of bone characteristics based on the propagation of sound through bone, the attenuation of that sound, and different processing techniques. QUS parameters and model predictions based on backscattered signals can discriminate non-fracture from fracture cases with accuracy comparable to standard bone mineral density (BMD). With advances in magnetic resonance imaging (MRI), bound water and pore water, or a porosity index, can be quantified in several long bones in vivo. Since such imaging-derived measurements correlate with the fracture resistance of bone, they potentially provide new BMD-independent predictors of fracture risk. While numerous measurements of mineral, organic matrix, and bound water by Raman spectroscopy correlate with the strength and toughness of cortical bone, the clinical assessment of person's bone quality using spatially offset Raman spectroscopy (SORS) requires advanced spectral processing techniques that minimize contaminating signals from fat, skin, and blood. Limiting exposure of patients to ionizing radiation, QUS, MRI, and SORS has the potential to improve the assessment of fracture risk and track changes of new therapies that target bone matrix and micro-structure.

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.

Total Hip Bone Mineral Density as an Indicator of Fracture Risk in Bisphosphonate-Treated Patients in a Real-World Setting

Bone mineral density (BMD) is an established measure used to diagnose patients with osteoporosis. In clinical trials, change in BMD has been shown to provide a reliable estimate of fracture risk reduction, and achieved BMD T-score has been shown to reflect the near-term risk of fracture. We aimed to test the association between BMD T-score and fracture risk in patients treated for osteoporosis in a real-world setting. This retrospective, observational cohort study included Swedish females aged ≥55 years who had a total hip BMD measurement at one of three participating clinics. Patients were separated into two cohorts: bisphosphonate-treated and bisphosphonate-naïve prior to BMD measurement, stratified by age and prior nonvertebral fracture status. The primary outcome was cumulative incidence of clinical fractures within 24 months of BMD measurement, with other fracture types included as secondary outcomes. Associations between T-score and fracture risk were estimated using proportional hazards regression and restricted cubic splines. A total of 15,395 patients were analyzed: 11,973 bisphosphonate-naïve and 3422 bisphosphonate-treated. In the 24 months following BMD measurement, 6.3% (95% confidence interval [CI], 5.9-6.7) of bisphosphonate-naïve and 8.4% (95% CI, 7.5-9.4) of bisphosphonate-treated patients experienced a clinical fracture. Strong inverse relationships between BMD T-score and fracture incidence were observed in both cohorts. Among bisphosphonate-naïve patients, this relationship appeared to plateau around T-score -1.5, indicating smaller marginal reductions in fracture risk above this value; bisphosphonate-treated patients showed a more consistent marginal change in fracture risk across the evaluated T-scores (-3.0 to -0.5). Trends remained robust regardless of age and prior fracture status. This real-world demonstration of a BMD-fracture risk association in both bisphosphonate-naïve and bisphosphonate-treated patients extends evidence from clinical trials and recent meta-regressions supporting the suitability of total hip BMD as a meaningful outcome for the clinical management of patients with osteoporosis. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

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.

The first step in an investigation of quantitative ultrasound as a technique for evaluating infant bone strength

This study's purpose is to evaluate whether bone speed of sound (SOS) data, a parameter of quantitative ultrasound, collected from an infant autopsy sample are comparable to data collected from healthy, living infants. We hypothesize that SOS values obtained from deceased term-born infants will fall within the normal range for healthy, living infants. The study sample consists of 351 deceased infants between the ages of 30 weeks gestation at birth to 1 year postnatal at the time of death receiving autopsies at the Harris County Institute of Forensic Sciences or Texas Children's Hospital in Houston, TX. Various multivariate and univariate statistics were used to examine the relationship between SOS and age, prematurity, and chronic illness. The results of an ANOVA comparing the study sample data to published data from healthy, living infants indicate the SOS data are comparable. Additionally, a MANOVA indicated significant differences in SOS related to prematurity (p = 0.001) and age (p < 0.001). Mean SOS was significantly greater among term-born infants (M = 3065.66, SD =165.05) than premature infants (M = 2969.71, SD =192.72). Age had a significant polynomial (cubic) relationship with SOS for both the premature and term groups (p < 0.001). Results suggest that bone from an infant autopsy sample is an appropriate surrogate to examine the relationship between SOS and determinants of bone strength. Therefore, future research will use this study sample to investigate the relationship between SOS and determinants of bone strength in infants.

Trabecular bone mineral density correlations using QCT: Central and peripheral human skeleton

Musculoskeletal injuries to the lower leg and foot-ankle joint are associated with external mechanical loads resulting from motor vehicle crashes, under body blasts, falls from height, or sports. As an intrinsic material property, the bone mineral density (BMD) is related to bone strength. The clinically recognized biological sites for BMD evaluation are the hip and spine. The focus of this study was to define the correlation between BMD from standard clinical sites (hip and lumbar spine) compared to BMD from non-standard sites (foot-ankle-distal tibia bones). Twenty-one post-mortem human subjects (PMHS) with mean age, height, and mass of 63 ± 11 years, 179 ± 7 cm, and 86 ± 13 kg, respectively were used for analysis. Clinical BMD software (Mindways Software, Inc.) was used for trabecular BMD quantification using quantitative computed tomography (QCT). In quantification of BMD of the foot-ankle-distal tibia (hind foot), the trabecular BMD of the talus (316 ± 86mg/cc) was highest followed by the distal tibia (238 ± 72 mg/cc) and then calcaneus (147 ± 51 mg/cc). To correlate BMD values from foot bone regions with the central skeleton BMD values within the same PMHS, there were 18 lumbar spine and 12 hip BMDs available. The BMD of the distal tibia correlated best with the hip intertrochanter BMD (R² of 0.72). Calcaneus BMD best correlated with the hip femoral neck BMD (R² = 0.64). In summary, the hind foot bone BMD values correlated better with the hip as compared to the lumbar spine BMD from the same PMHS. These findings indicate that, in the absence of a direct measure of foot-bone BMD, hip BMD might be a better predictor of injury risk to hind foot rather than lumbar spine BMD, or alternatively, calcaneal trabecular BMD can be used to predict the risk of injury to hip. Further, these relationships between central and peripheral regions can also be implemented in finite element models for improved failure predictions.

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.

Computer-aided diagnosis systems for osteoporosis detection: a comprehensive survey

Computer-aided diagnosis (CAD) has revolutionized the field of medical diagnosis. They assist in improving the treatment potentials and intensify the survival frequency by early diagnosing the diseases in an efficient, timely, and cost-effective way. The automatic segmentation has led the radiologist to successfully segment the region of interest to improve the diagnosis of diseases from medical images which is not so efficiently possible by manual segmentation. The aim of this paper is to survey the vision-based CAD systems especially focusing on the segmentation techniques for the pathological bone disease known as osteoporosis. Osteoporosis is the state of the bones where the mineral density of bones decreases and they become porous, making the bones easily susceptible to fractures by small injury or a fall. The article covers the image acquisition techniques for acquiring the medical images for osteoporosis diagnosis. The article also discusses the advanced machine learning paradigms employed in segmentation for osteoporosis disease. Other image processing steps in osteoporosis like feature extraction and classification are also briefly described. Finally, the paper gives the future directions to improve the osteoporosis diagnosis and presents the proposed architecture. Graphical abstract.

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.

In Vivo Measurements of Cortical Thickness and Porosity at the Proximal Third of the Tibia Using Guided Waves: Comparison with Site-Matched Peripheral Quantitative Computed Tomography and Distal High-Resolution Peripheral Quantitative Computed Tomography

The aim of this study was to estimate cortical porosity (Ct.Po) and cortical thickness (Ct.Th) using 500-kHz bi-directional axial transmission (AT). Ct.Th_AT and Ct.Po_AT were obtained at the tibia in 15 patients from a 2-D transverse isotropic free plate model fitted to measured guided wave dispersion curves. The velocities of the first arriving signal (υ_FAS) and A₀ mode (υ_A0) were also determined. Site-matched peripheral quantitative computed tomography (pQCT) provided volumetric cortical bone mineral density (Ct.vBMD_pQCT) and Ct.Th_pQCT. Good agreement was found between Ct.Th_AT and Ct.Th_pQCT (R² = 0.62, root mean square error [RMSE] = 0.39 mm). Ct.vBMD_pQCT correlated with Ct.Po_AT (R² = 0.57), υ_FAS (R² = 0.43) and υ_A0 (R² = 0.28). Furthermore, a significant correlation was found between AT and distal high-resolution pQCT. The measurement ofcortical parameters at the tibia using guided waves might improve the prediction of bone fractures in a cost-effective and radiation-free manner.

Recent advancements in the analysis of bone microstructure: New dimensions in forensic anthropology

Bone is a mechanically active, three-dimensionally (3D) complex, and dynamic tissue that changes in structure over the human lifespan. Bone tissue exists and remodels in 3D and changes over time, introducing a fourth dimension. The products of the remodelling process, secondary and fragmentary osteons, have been studied substantially using traditional two-dimensional (2D) techniques. As a result, much has been learned regarding the biological information encrypted in the histomorphology of bone, yielding a wealth of information relating to skeletal structure and function. Three-dimensional imaging modalities, however, hold the potential to provide a much more comprehensive understanding of bone microarchitecture. The visualization and analysis of bone using high-resolution 3D imaging will improve current understandings of bone biology and have numerous applications in both biological anthropology and biomedicine. Through recent technological advancements, we can hone current anthropological applications of the analysis of bone microstructure and accelerate research into the third and fourth dimensional realms. This review will explore the methodological approaches used historically by anthropologists to assess cortical bone microstructure, spanning from histology to current ex vivo imaging modalities, discuss the growing capabilities of in vivo imaging, and conclude with an introduction of novel non-histological modalities for investigating bone quality.

FRAME Study: The Foundation Effect of Building Bone With 1 Year of Romosozumab Leads to Continued Lower Fracture Risk After Transition to Denosumab

Romosozumab is a bone-forming agent with a dual effect of increasing bone formation and decreasing bone resorption. In FRActure study in postmenopausal woMen with ostEoporosis (FRAME), postmenopausal women with osteoporosis received romosozumab 210 mg s.c. or placebo once monthly for 12 months, followed by denosumab 60 mg s.c. once every 6 months in both groups for 12 months. One year of romosozumab increased spine and hip BMD by 13% and 7%, respectively, and reduced vertebral and clinical fractures with persistent fracture risk reduction upon transition to denosumab over 24 months. Here, we further characterize the BMD gains with romosozumab by quantifying the percentages of patients who responded at varying magnitudes; report the mean T-score changes from baseline over the 2-year study and contrast these results with the long-term BMD gains seen with denosumab during Fracture REduction Evaluation of Denosumab in Osteoporosis every 6 Months (FREEDOM) and its Extension studies; and assess fracture incidence rates in year 2, when all patients received denosumab. Among 7180 patients (n = 3591 placebo, n = 3589 romosozumab), most romosozumab-treated patients experienced ≥3% gains in BMD from baseline at month 12 (spine, 96%; hip, 78%) compared with placebo (spine, 22%; hip, 16%). For romosozumab patients, mean absolute T-score increases at the spine and hip were 0.88 and 0.32, respectively, at 12 months (placebo: 0.03 and 0.01) and 1.11 and 0.45 at 24 months (placebo-to-denosumab: 0.38 and 0.17), with the 2-year gains approximating the effect of 7 years of continuous denosumab administration. Patients receiving romosozumab versus placebo in year 1 had significantly fewer vertebral fractures in year 2 (81% relative reduction; p < 0.001), with fewer fractures consistently observed across other fracture categories. The data support the clinical benefit of rebuilding the skeletal foundation with romosozumab before transitioning to antiresorptive therapy. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals, Inc.

Prediction of fracture load and stiffness of the proximal femur by CT-based specimen specific finite element analysis: cadaveric validation study

Background

Finite element analysis (FEA) of the proximal femur has been previously validated with large mesh size, but these were insufficient to simulate the model with small implants in recent studies. This study aimed to validate the proximal femoral computed tomography (CT)-based specimen-specific FEA model with smaller mesh size using fresh frozen cadavers.

Methods

Twenty proximal femora from 10 cadavers (mean age, 87.1 years) were examined. CT was performed on all specimens with a calibration phantom. Nonlinear FEA prediction with stance configuration was performed using Mechanical Finder (mesh,1.5 mm tetrahedral elements; shell thickness, 0.2 mm; Poisson’s coefficient, 0.3), in comparison with mechanical testing. Force was applied at a fixed vertical displacement rate, and the magnitude of the applied load and displacement were continuously recorded. The fracture load and stiffness were calculated from force–displacement curve, and the correlation between mechanical testing and FEA prediction was examined.

Results

A pilot study with one femur revealed that the equations proposed by Keller for vertebra were the most reproducible for calculating Young’s modulus and the yield stress of elements of the proximal femur. There was a good linear correlation between fracture loads of mechanical testing and FEA prediction (R² = 0.6187) and between the stiffness of mechanical testing and FEA prediction (R² = 0.5499). There was a good linear correlation between fracture load and stiffness (R² = 0.6345) in mechanical testing and an excellent correlation between these (R² = 0.9240) in FEA prediction.

Conclusions

CT-based specimen-specific FEA model of the proximal femur with small element size was validated using fresh frozen cadavers. The equations proposed by Keller for vertebra were found to be the most reproducible for the proximal femur in elderly people.

Comparison of non-invasive assessments of strength of the proximal femur

It is not clear which non-invasive method is most effective for predicting strength of the proximal femur in those at highest risk of fracture. The primary aim of this study was to compare the abilities of dual energy X-ray absorptiometry (DXA)-derived aBMD, quantitative computed tomography (QCT)-derived density and volume measures, and finite element analysis (FEA)-estimated strength to predict femoral failure load. We also evaluated the contribution of cortical and trabecular bone measurements to proximal femur strength. We obtained 76 human cadaveric proximal femurs (50 women and 26 men; age 74±8.8years), performed imaging with DXA and QCT, and mechanically tested the femurs to failure in a sideways fall configuration at a high loading rate. Linear regression analysis was used to construct the predictive model between imaging outcomes and experimentally-measured femoral strength for each method. To compare the performance of each method we used 3-fold cross validation repeated 10 times. The bone strength estimated by QCT-based FEA predicted femoral failure load (R²_adj=0.78, 95%CI 0.76-0.80; RMSE=896N, 95%CI 830-961) significantly better than femoral neck aBMD by DXA (R²_adj=0.69, 95%CI 0.66-0.72; RMSE=1011N, 95%CI 952-1069) and the QCT-based model (R²_adj=0.73, 95%CI 0.71-0.75; RMSE=932N, 95%CI 879-985). Both cortical and trabecular bone contribute to femoral strength, the contribution of cortical bone being higher in femurs with lower trabecular bone density. These findings have implications for optimizing clinical approaches to assess hip fracture risk. In addition, our findings provide new insights that will assist in interpretation of the effects of osteoporosis treatments that preferentially impact cortical versus trabecular bone.

Sideways fall-induced impact force and its effect on hip fracture risk: a review

Osteoporotic hip fracture, mostly induced in falls among the elderly, is a major health burden over the world. The impact force applied to the hip is an important factor in determining the risk of hip fracture. However, biomechanical researches have yielded conflicting conclusions about whether the fall-induced impact force can be accurately predicted by the available models. It also has been debated whether or not the effect of impact force has been considered appropriately in hip fracture risk assessment tools. This study aimed to provide a state-of-the-art review of the available methods for predicting the impact force, investigate their strengths/limitations, and suggest further improvements in modeling of human body falling.

METHODS

We divided the effective parameters on impact force to two categories: (1) the parameters that can be determined subject-specifically and (2) the parameters that may significantly vary from fall to fall for an individual and cannot be considered subject-specifically.

RESULTS

The parameters in the first category can be investigated in human body fall experiments. Video capture of real-life falls was reported as a valuable method to investigate the parameters in the second category that significantly affect the impact force and cannot be determined in human body fall experiments.

CONCLUSIONS

The analysis of the gathered data revealed that there is a need to develop modified biomechanical models for more accurate prediction of the impact force and appropriately adopt them in hip fracture risk assessment tools in order to achieve a better precision in identifying high-risk patients. Graphical abstract Impact force to the hip induced in sideways falls is affected by many parameters and may remarkably vary from subject to subject.

Distal skeletal tibia assessed by HR-pQCT is highly correlated with femoral and lumbar vertebra failure loads

Dual energy X-ray absorptiometry (DXA) is the standard for assessing fragility fracture risk using areal bone mineral density (aBMD), but only explains 60-70% of the variation in bone strength. High-resolution peripheral quantitative computed tomography (HR-pQCT) provides 3D-measures of bone microarchitecture and volumetric bone mineral density (vBMD), but only at the wrist and ankle. Finite element (FE) models can estimate bone strength with 86-95% precision. The purpose of this study is to determine how well vBMD and FE bone strength at the wrist and ankle relate to fracture strength at the hip and spine, and to compare these relationships with DXA measured directly at those axial sites. Cadaveric samples (radius, tibia, femur and L4 vertebra) were compared within the same body. The radius and tibia specimens were assessed using HR-pQCT to determine vBMD and FE failure load. aBMD from DXA was measured at the femur and L4 vertebra. The femur and L4 vertebra specimens were biomechanically tested to determine failure load. aBMD measures of the axial skeletal sites strongly correlated with the biomechanical strength for the L4 vertebra (r=0.77) and proximal femur (r=0.89). The radius correlated significantly with biomechanical strength of the L4 vertebra for vBMD (r=0.85) and FE-derived strength (r=0.72), but not with femur strength. vBMD at the tibia correlated significantly with femoral biomechanical strength (r=0.74) and FE-estimated strength (r=0.83), and vertebral biomechanical strength for vBMD (r=0.97) and FE-estimated strength (r=0.91). The higher correlations at the tibia compared to radius are likely due to the tibia's weight-bearing function.

Advances in imaging approaches to fracture risk evaluation

Fragility fractures are a growing problem worldwide, and current methods for diagnosing osteoporosis do not always identify individuals who require treatment to prevent a fracture and may misidentify those not a risk. Traditionally, fracture risk is assessed using dual-energy X-ray absorptiometry, which provides measurements of areal bone mineral density at sites prone to fracture. Recent advances in imaging show promise in adding new information that could improve the prediction of fracture risk in the clinic. As reviewed herein, advances in quantitative computed tomography (QCT) predict hip and vertebral body strength; high-resolution HR-peripheral QCT (HR-pQCT) and micromagnetic resonance imaging assess the microarchitecture of trabecular bone; quantitative ultrasound measures the modulus or tissue stiffness of cortical bone; and quantitative ultrashort echo-time MRI methods quantify the concentrations of bound water and pore water in cortical bone, which reflect a variety of mechanical properties of bone. Each of these technologies provides unique characteristics of bone and may improve fracture risk diagnoses and reduce prevalence of fractures by helping to guide treatment decisions.

One year of abaloparatide, a selective peptide activator of the PTH1 receptor, increased bone mass and strength in ovariectomized rats

Abaloparatide is a novel 34 amino acid peptide selected to be a potent and selective activator of the parathyroid hormone receptor 1 (PTHR1) signaling pathway. The effects of 12months of abaloparatide treatment on bone mass, bone strength and bone quality was assessed in osteopenic ovariectomized (OVX) rats. SD rats were subjected to OVX or sham surgery at 6months of age and left untreated for 3months to allow OVX-induced bone loss. Eighteen OVX rats were sacrificed after this bone depletion period, and the remaining OVX rats received daily s.c. injections of vehicle (n=18) or abaloparatide at 1, 5 or 25μg/kg/d (n=18/dose level) for 12months. Sham controls (n=18) received vehicle daily. Bone changes were assessed by DXA and pQCT after 0, 3, 6 or 12months of treatment, and destructive biomechanical testing was conducted at month 12 to assess bone strength and bone quality. Abaloparatide dose-dependently increased bone mass at the lumbar spine and at the proximal and diaphyseal regions of the tibia and femur. pQCT revealed that increased cortical bone volume at the tibia was a result of periosteal expansion and endocortical bone apposition. Abaloparatide dose-dependently increased structural strength of L4-L5 vertebral bodies, the femur diaphysis, and the femur neck. Increments in peak load for lumbar spine and the femur diaphysis of abaloparatide-treated rats persisted even after adjusting for treatment-related increments in BMC, and estimated material properties were maintained or increased at the femur diaphysis with abaloparatide. The abaloparatide groups also exhibited significant and positive correlations between bone mass and bone strength at these sites. These data indicate that gains in cortical and trabecular bone mass with abaloparatide are accompanied by and correlated with improvements in bone strength, resulting in maintenance or improvement in bone quality. Thus, this study demonstrated that long-term daily administration of abaloparatide to osteopenic OVX rats led to dose-dependent improvements in bone mass, geometry and strength.

Dietary restrictions, bone density, and bone quality

Caloric restriction (CR), protein restriction (PR), and specific amino acid restriction (e.g., methionine restriction (MR)) are different dietary interventions that have been confirmed with regard to their comprehensive benefits to metabolism and health. Based on bone densitometric measurements, weight loss induced by dietary restriction is known to be accompanied by reduced areal bone mineral density, bone mass, and/or bone size, and it is considered harmful to bone health. However, because of technological advancements in bone densitometric instruments (e.g., high-resolution X-ray tomography), dietary restrictions have been found to cause a reduction in bone mass/size rather than volumetric bone mineral density. Furthermore, when considering bone quality, bone health consists of diverse indices that cannot be fully represented by densitometric measurements alone. Indeed, there is evidence that moderate dietary restrictions do not impair intrinsic bone material properties, despite the reduction in whole-bone strength because of a smaller bone size. In the present review, we integrate research evidence from traditional densitometric measurements, metabolic status assays (e.g., energy metabolism, oxidative stresses, and inflammatory responses), and biomaterial analyses to provide revised conclusions regarding the effects of CR, PR, and MR on the skeleton.

Correlation between Parameters of Calcaneal Quantitative Ultrasound and Hip Structural Analysis in Osteoporotic Fracture Patients

Background

Calcaneal quantitative ultrasound (QUS), which is used in the evaluation of osteoporosis, is believed to be intimately associated with the characteristics of the proximal femur. However, the specific associations of calcaneal QUS with characteristics of the hip sub-regions remain unclear.

Design

A cross-sectional assessment of 53 osteoporotic patients was performed for the skeletal status of the heel and hip.

Methods

We prospectively enrolled 53 female osteoporotic patients with femoral fractures. Calcaneal QUS, dual energy X-ray absorptiometry (DXA), and hip structural analysis (HSA) were performed for each patient. Femoral heads were obtained during the surgery, and principal compressive trabeculae (PCT) were extracted by a three-dimensional printing technique-assisted method. Pearson’s correlation between QUS measurement with DXA, HSA-derived parameters and Young’s modulus were calculated in order to evaluate the specific association of QUS with the parameters for the hip sub-regions, including the femoral neck, trochanteric and Ward’s areas, and the femoral shaft, respectively.

Results

Significant correlations were found between estimated BMD (Est.BMD) and BMD of different sub-regions of proximal femur. However, the correlation coefficient of trochanteric area (r = 0.356, p = 0.009) was higher than that of the neck area (r = 0.297, p = 0.031) and total proximal femur (r = 0.291, p = 0.034). Furthermore, the quantitative ultrasound index (QUI) was significantly correlated with the HSA-derived parameters of the trochanteric area (r value: 0.315–0.356, all p<0.05) as well as with the Young’s modulus of PCT from the femoral head (r = 0.589, p<0.001).

Conclusion

The calcaneal bone had an intimate association with the trochanteric cancellous bone. To a certain extent, the parameters of the calcaneal QUS can reflect the characteristics of the trochanteric area of the proximal hip, although not specifically reflective of those of the femoral neck or shaft.

Prediction of proximal femur strength by a quantitative computed tomography-based finite element method--Creation of predicted strength data of the proximal femur according to age range in a normal population

OBJECTIVE

The objective of this study was to investigate the factors that affect the predicted bone strength of proximal femur in Japanese population.

METHODS

Participants (552 men and 273 women) in a health checkup program with computed tomography (CT) at the University of Tokyo Hospital were enrolled in this study. Three-dimensional finite element models of the proximal femur were constructed from CT data of the participants with simultaneous scans of a calibration phantom containing hydroxyapatite rods. Multiple regression analysis was performed to analyze the relationship between the predicted bone strength and clinical factors.

RESULTS

Average predicted strength of proximal femur was lower in women than in men in all age ranges. Predicted bone strength in women under both stance and fall configurations significantly decreased with age, and that in men had the tendency to decrease with age. Body weight positively affected the predicted bone strength in both men and women.

CONCLUSIONS

This is the first cross-sectional analysis of the predicted bone strength of the proximal femur in Japanese population of wide age range. Age and body weight critically affected bone strength of proximal femur determined by quantitative CT-based finite element method, in particular in women, under both stance and fall configurations.

Strain distribution in the proximal Human femur during in vitro simulated sideways fall

This study assessed: (i) how the magnitude and direction of principal strains vary for different sideways fall loading directions; (ii) how the principal strains for a sideways fall differ from physiological loading directions; (iii) the fracture mechanism during a sideways fall. Eleven human femurs were instrumented with 16 triaxial strain gauges each. The femurs were non-destructively subjected to: (a) six loading configurations covering the range of physiological loading directions; (b) 12 configurations simulating sideways falls. The femurs were eventually fractured in a sideways fall configuration while high-speed cameras recorded the event. When the same force magnitude was applied, strains were significantly larger in a sideways fall than for physiological loading directions (principal compressive strain was 70% larger in a sideways fall). Also the compressive-to-tensile strain ratio was different: for physiological loading the largest compressive strain was only 30% larger than the largest tensile strain; but for the sideways fall, compressive strains were twice as large as the tensile strains. Principal strains during a sideways fall were nearly perpendicular to the direction of principal strains for physiological loading. In the most critical regions (medial part of the head-neck) the direction of principal strain varied by less than 9° between the different physiological loading conditions, whereas it varied by up to 17° between the sideways fall loading conditions. This was associated with a specific fracture mechanism during sideways fall, where failure initiated on the superior-lateral side (compression) followed by later failure of the medially (tension), often exhibiting a two-peak force-displacement curve.

Intraoperative mechanical measurement of bone quality with the DensiProbe

Reduced bone stock can result in fractures that mostly occur in the spine, distal radius, and proximal femur. In case of operative treatment, osteoporosis is associated with an increased failure rate. To estimate implant anchorage, mechanical methods seem to be promising to measure bone strength intraoperatively. It has been shown that the mechanical peak torque correlates with the local bone mineral density and screw failure load in hip, hindfoot, humerus, and spine in vitro. One device to measure mechanical peak torque is the DensiProbe (AO Research Institute, Davos, Switzerland). The device has shown its effectiveness in mechanical peak torque measurement in mechanical testing setups for the use in hip, hindfoot, and spine. In all studies, the correlation of mechanical torque measurement and local bone mineral density and screw failure load could be shown. It allows the surgeon to judge local bone strength intraoperatively directly at the region of interest and gives valuable information if additional augmentation is needed. We summarize methods of this new technique, its advantages and limitations, and give an overview of actual and possible future applications.

The effects of body mass index and sex on impact force and effective pelvic stiffness during simulated lateral falls

BACKGROUND

The incidence of hip fractures is highest for underweight females with low body mass index (BMI). However, it is unknown how these factors influence impact dynamics during in-vivo lateral hip impacts.We used a pelvis release paradigm to compare: (1) absolute and normalized forces applied to the femur-pelvis system across sex and BMI groups; (2) the force-prediction accuracy of vibration-based versus force-deflection-based estimates of effective pelvic stiffness; and (3) effective pelvic stiffness between BMI and sex groups.

METHODS

Twenty-eight persons participated (7 low-BMI females, 7 low-BMI males, 7 high-BMI females, 7 high-BMI males,with BMI criteria of <22.5 and >28 for low- and high-BMI groups respectively). The participant's pelvis was released from heights of 0 to 5 cm. A force plate measured impact loads, while a motion capture system measured pelvic deflection.

FINDINGS

Peak impact forces were 22.6% higher, while normalized peak forces were 31.2% lower, for high- compared to low-BMI participants. Accuracy of peak force predictions improved by 25% for the force-deflection versus the vibration-based stiffness estimation method. Effective pelvic stiffness was greater for males than females, but no significant differences were observed between BMI groups.

INTERPRETATION

This study adds to clinical understanding of the effects of sex and BMI on impact dynamics during falls on the hip, and raises questions about the biomechanical mechanisms underlying the protective role of high BMI on hip fracture risk. Understanding the relationship between impact mechanics and faller characteristics should lead to more effective prevention of hip fractures.

A NEW PARADIGM FOR THE IN VITRO SIMULATION OF SIDEWAYS FALL LOADING OF THE PROXIMAL HUMAN FEMUR

Although the direction of loads applied to the proximal human femur is unpredictable during sideways fall, most in vitro and numerical simulations refer to a single loading condition (15° internal rotation; 10° adduction), which has been anecdotally suggested in the 1950s. The aim of the present study was to improve in vitro simulations of sideways falls on the proximal femur.

An in vitro setup was developed that allowed exploring a range of loading directions +/-90° internal–external rotation; 0°–50° adduction). To enable accurate control of the loading conditions (direction and magnitude of all load components applied to the femur), the setup included a number of low-friction linear and rotary bearings. The setup was instrumented with an axial and a torsional load cell, three displacement transducers and a rotation transducer to monitor the most significant components of load/displacement during testing. The strain distribution was measured on the bone surface (16 triaxial strain gauges, 2,000 Hz). Fracture was recorded with a high-speed camera.

The setup was successfully tested on a cadaveric femur non-destructively (12 loading configurations) and destructively (15° internal rotation; 10° adduction). All measurements were highly repeatable (the displacements of the femoral head varied by < 2% between repetitions; the tilt in the frontal plane by < 0.05°; and strain varied on average 0.34% between repetitions). The displacement of the femoral head varied by over 50% when the same force was applied in different directions. Principal strains at the same location varied by over 70%, depending on the direction of the applied force. The high-speed video enabled the identification of the point of fracture initiation.

This study has shown that a new paradigm for testing the proximal femur (including improved testing conditions and a variety of loading configurations) can provide more accurate and more extensive information about the state of strain.

Bone mineral density and geometry parameters determined in vitro from dual-energy digital radiography images in the assessment of bone maximal load of reindeer femora

BACKGROUND

Dual-energy digital radiography (DEDR) has been shown to be a potential method to determine bone mineral density (BMD) and predict maximal load with similar accuracy as standard bone densitometry using DXA (dual-energy X-ray absorptiometry). In addition to bone density, bone geometry has also been shown to have effect on bone fragility and fracture risk.

PURPOSE

To examine the combination of BMD and geometry parameters, as determined from a DEDR experiment, to predict bone maximal load.

MATERIAL AND METHODS

Reindeer femora (n = 47) were imaged at two energies (79 kVp and 100 kVp) using a clinical digital radiography system. BMD was determined in four regions from these images using the DXA calculation principle. Various geometrical parameters were determined from the 79 kVp image. Femora were mechanically tested using axial loading configuration. Pearson correlation coefficients were determined between geometrical parameters and BMDs or maximal load. Multiple stepwise linear regression analysis was used to find the best combination to predict bone maximal load.

RESULTS

From the geometrical parameters, femoral shaft diameter (FSD) and femoral neck axis length (FNAL) correlated best with the maximal load (r = 0.629 and r = 0.446, P < 0.01, respectively). The best combination of parameters to predict bone fragility was BMD at Ward's triangle, FSD and FNAL (r = 0.787, P < 0.05), whereas the correlation coefficient between BMD at Ward's triangle and maximal load was 0.653 (P < 0.05).

CONCLUSION

The combination of DEDR-based BMD and geometrical parameters predicts reindeer bone maximal load with reasonable accuracy and the combined analysis improves the prediction of maximal load compared to BMD prediction only.

Stemmed TKA in a femur with a total hip arthroplasty: is there a safe distance between the stem tips?

When a stemmed TKA is needed in a femur in which a THA is already present, choosing an appropriate length for the TKA stem is crucial. Many surgeons intuitively fear that the distance between the stem tips correlates with the femur risk for fracture (RF). However, to date, no biomechanical data to support this intuition are available. Therefore, in this study, the RF in such a configuration was determined and compared for several activities, using a finite element modeling technique. During gait and sideways falling no difference in RF among different stem lengths was shown. However, a clear threshold appears during four-point bending. Stem tip distances shorter than 110 mm dramatically increased RF and, in osteoporotic bone, will certainly lead to fracture (RF>1) and thus should be avoided.

Bone health comparison in seven Asian countries using calcaneal ultrasound

BACKGROUND

Bone density measurements by DXA are not feasible for large population studies, whereas portable ultrasound heel scanners can provide a practical way of assessing bone health status. The purpose of this study was to assess bone health in seven Asian countries using heel ultrasound.

METHODS

Stiffness index (SI) was measured and T-scores generated against an Asian database were recorded for 598,757 women and 173,326 men aged over 21 years old using Lunar Achilles (GE Healthcare) heel scanners. The scanners were made available in public centres in Singapore, Vietnam, Malaysia, Taiwan, Thailand, Indonesia and the Philippines.

RESULTS

The mean SI was higher for men than women. In women SI as well as T-scores declined slowly until approximately 45 years of age, then declined rapidly to reach a mean T-score of < -2.5 at about 71-75 years of age. For men, SI as well as the T-score showed a slow steady decline to reach a mean of -2.0 to -2.5 at about 81-85 years. The results for females indicate that there are differences in the rate of decline between countries (significant differences between the slopes at P < 0.05). Vietnam had the fastest decrease for both T-Score and SI, resulting in this population having the poorest bone health of all countries at older ages. The results for males aged 46-85 years indicate that there are no significant differences in the rate of decline between countries for SI and T-Score. In both men and women aged 46-85 years, Vietnam and Indonesia have the lowest SI as well as T-Score for all age groups. For Vietnam and Indonesia, more than 50% of the women could be at risk of having osteoporosis and related fractures after the age of 70, while in Thailand and the Philippines this was >80 years.

CONCLUSIONS

The heel scan data shows a high degree of poor bone health in both men and women in Asian countries, raising concern about the possible increase in fractures with ageing and the expected burden on the public health system.

A nonlinear QCT-based finite element model validation study for the human femur tested in two configurations in vitro

PURPOSE

Femoral fracture is a common medical problem in osteoporotic individuals. Bone mineral density (BMD) is the gold standard measure to evaluate fracture risk in vivo. Quantitative computed tomography (QCT)-based homogenized voxel finite element (hvFE) models have been proved to be more accurate predictors of femoral strength than BMD by adding geometrical and material properties. The aim of this study was to evaluate the ability of hvFE models in predicting femoral stiffness, strength and failure location for a large number of pairs of human femora tested in two different loading scenarios.

METHODS

Thirty-six pairs of femora were scanned with QCT and total proximal BMD and BMC were evaluated. For each pair, one femur was positioned in one-legged stance configuration (STANCE) and the other in a sideways configuration (SIDE). Nonlinear hvFE models were generated from QCT images by reproducing the same loading configurations imposed in the experiments. For experiments and models, the structural properties (stiffness and ultimate load), the failure location and the motion of the femoral head were computed and compared.

RESULTS

In both configurations, hvFE models predicted both stiffness (R(2)=0.82 for STANCE and R(2)=0.74 for SIDE) and femoral ultimate load (R(2)=0.80 for STANCE and R(2)=0.85 for SIDE) better than BMD and BMC. Moreover, the models predicted qualitatively well the failure location (66% of cases) and the motion of the femoral head.

CONCLUSIONS

The subject specific QCT-based nonlinear hvFE model cannot only predict femoral apparent mechanical properties better than densitometric measures, but can additionally provide useful qualitative information about failure location.

Frequency specific ultrasound attenuation is sensitive to trabecular bone structure

This study investigated the efficacy of frequency modulated ultrasound attenuation in the assessment of the trabecular structural properties. Four frequency modulated signals were created to represent four frequency bands centered at 500 kHz, 900 kHz, 1.3 MHz and 1.7 MHz with the bandwidth of 400 kHz. Five 1-cm trabecular cubes were harvested from fresh bovine distal femur. The cubes underwent four steps of demineralization process to expand the sample size to 25 with the greater variations of the structural properties for the better correlation study. Pearson correlation study was performed between the ultrasound attenuation in four frequency bands and the trabecular structural properties. The results showed that correlations of frequency modulated ultrasound attenuation to the trabecular structural properties are dependent on frequency bands. The attenuation in proximal-distal orientation had the highest correlation to BV/TV (R(2) = 0.73, p < 0.001) and trabecular thickness (R(2) = 0.50, p < 0.001) at the frequency band centered at 1.7 MHz. It was equivalent in the four frequency bands in correlation to the trabecular number (average R(2) = 0.80, p < 0.001) and to the trabecular separation (average R(2) = 0.83, p < 0.001). The attenuation in anterio-posterial orientation had the highest correlation to BV/TV (R(2) = 0.80, p < 0.001) and trabecular thickness (R(2) = 0.71, p < 0.001) at the frequency band centered at 1.3 MHz. The attenuation in the first frequency band was the most sensitive to the trabecular number (R(2) = 0.71, p < 0.001) and trabecular separation (R(2) = 0.80, p < 0.001). No significant correlation was observed for the attenuation in medial-lateral orientation across the four frequency bands.

Relative contributions of porosity and mineralized matrix properties to the bulk axial ultrasonic wave velocity in human cortical bone

Velocity of ultrasound waves has proved to be a useful indicator of bone biomechanical competence. A detailed understanding of the dependence of ultrasound parameters such as velocity on bone characteristics is a key to the development of bone quantitative ultrasound (QUS). The objective of this study is to investigate the relative contributions of porosity and mineralized matrix properties to the bulk compressional wave velocity (BCV) along the long bone axis. Cross-sectional slabs from the diaphysis of four human femurs were included in the study. Seven regions of interest (ROIs) were selected in each slab. BCV was measured in through-transmission at 5 MHz. Impedance of the mineralized matrix (Z(m)) and porosity (Por) were obtained from 50 MHz scanning acoustic microscopy. Por and Z(m) had comparable effects on BCV along the bone axis (R=-0.57 and R=0.72, respectively).

The factor-of-risk biomechanical approach predicts hip fracture in men and women: the Framingham Study

SUMMARY

We examined the relation between a biomechanical measure, factor-of-risk, and hip fracture risk in 1,100 men and women from the Framingham Study and found that it predicted hip fracture (men, ORs of 1.8; women, 1.2-1.4).

INTRODUCTION

Alternative methods of predicting hip fracture are needed since 50% of adults who fracture do not have osteoporosis by bone mineral density (BMD) measurements. One method, factor-of-risk (Φ), computes the ratio of force on the hip in a fall to femoral strength. We examined the relation between Φ and hip fracture in 1,100 subjects from the Framingham Study with measured hip BMD, along with weight, height, and age, collected in 1988-1989.

METHODS

We estimated both peak and attenuated force applied to the hip in a sideways fall from standing height, where attenuated force incorporated cushioning effects of trochanteric soft tissue. Femoral strength was estimated from femoral neck BMD, using cadaveric femoral strength data. Sex-specific, age-adjusted survival models were used to calculate hazard ratios (HR) and 95% confidence intervals for the relation between Φ (peak), Φ (attenuated), and their components with hip fracture.

RESULTS

In 425 men and 675 women (mean age, 76 years), 136 hip fractures occurred over median follow-up of 11.3 years. Factor-of-risk, Φ, was associated with increased age-adjusted risk for hip fracture. One standard deviation increase in Φ (peak) and Φ (attenuated) was associated with HR of 1.88 and 1.78 in men and 1.23 and 1.41 in women, respectively. Examining components of Φ, in women, we found fall force and soft tissue thickness were predictive of hip fracture independent of femoral strength (was estimated from BMD).

CONCLUSIONS

Thus, both Φ (peak) and Φ (attenuated) predict hip fracture in men and women. These findings suggest additional studies of Φ predicting hip fracture using direct measurements of trochanteric soft tissue.

Prediction of femoral fracture load: cross-sectional study of texture analysis and geometric measurements on plain radiographs versus bone mineral density

PURPOSE

To use standard radiographs to determine which combination of co-occurrence textural parameters, geometric measurements, and cortical thickness measurements from femur radiographs provided the best estimate of femoral failure load and to compare these with total hip dual-energy x-ray absorptiometry bone mineral density (BMD) evaluation.

MATERIALS AND METHODS

Digital radiographs of 40 pairs of excised femurs (24 women, 16 men; mean age, 82 years + or - 12 [standard deviation]) were obtained. Regions of interest in the femoral neck, greater trochanter, intertrochanteric area, and femoral head were then selected. Three textural parameters derived from a co-occurrence matrix were estimated with imaging software. Neck-shaft angle, femoral neck axis length, calcar femorale thickness, and internal and external femoral shaft thickness were assessed. The femurs were randomly allocated to single-stance (femoral neck fracture) or side-impact (intertrochanteric fracture) configurations for failure load measurement.

RESULTS

Textural parameters correlated significantly with site-matched BMD. Stepwise regression analysis was performed, and total hip BMD explained 73% and 78% of the failure load in single-stance and side-impact configurations, respectively. Combining internal femoral shaft thickness with one or two textural parameters explained 72%-79% of failure load variance in the single-stance configuration and 63%-76% of failure load variance in the side-impact configuration.

CONCLUSION

In these excised femurs, combining textural parameters with cortical thickness measurements had a performance comparable to that of BMD alone in the explanation of femoral failure load.

Effect of hip protectors, falling angle and body mass index on pressure distribution over the hip during simulated falls

BACKGROUND

We examined how a soft shell hip protector affects the magnitude and distribution of force to the hip during simulated falls, and how the protective effect depends on the fall direction and the amount of soft tissue padding over the hip.

METHODS

Fourteen young women with either high or low body mass index participated in a "pelvis release experiment" that simulated falls resulting in either lateral, anterolateral or posterolateral impact to the pelvis with/without a soft shell hip protector. Outcome variables were the magnitude and location of peak pressure (d, theta) with respect to the greater trochanter, total impact force, and percent force applied to four defined hip regions.

FINDINGS

The soft shell hip protector reduced peak pressure by 70%. The effect was two times greater in low than high body mass index individuals. The protector shunted the peak pressure distally along the shaft of the femur (d=52 mm (SD 22), theta=-21 degrees (SD 49) in the unpadded trials versus d=81 mm (SD 23), theta=-10 degrees (SD 35) in the padded trials). Peak force averaged 12% greater in posterolateral and 17% lower in anterolateral than lateral falls.

INTERPRETATION

Our results indicate that the hip protector we tested had a much stronger protective benefit for low than high body mass index individuals. Next generation protectors might be developed for improved shunting of pressure away from the femur, improved protection during posterolateral falls, and greater force attenuation for low body mass index individuals.

Hip protectors: recommendations for biomechanical testing--an international consensus statement (part I)

INTRODUCTION

Hip protectors represent a promising strategy for preventing fall-related hip fractures. However, clinical trials have yielded conflicting results due, in part, to lack of agreement on techniques for measuring and optimizing the biomechanical performance of hip protectors as a prerequisite to clinical trials.

METHODS

In November 2007, the International Hip Protector Research Group met in Copenhagen to address barriers to the clinical effectiveness of hip protectors. This paper represents an evidence-based consensus statement from the group on recommended methods for evaluating the biomechanical performance of hip protectors.

RESULTS AND CONCLUSIONS

The primary outcome of testing should be the percent reduction (compared with the unpadded condition) in peak value of the axial compressive force applied to the femoral neck during a simulated fall on the greater trochanter. To provide reasonable results, the test system should accurately simulate the pelvic anatomy, and the impact velocity (3.4 m/s), pelvic stiffness (acceptable range: 39-55 kN/m), and effective mass of the body (acceptable range: 22-33 kg) during impact. Given the current lack of clear evidence regarding the clinical efficacy of specific hip protectors, the primary value of biomechanical testing at present is to compare the protective value of different products, as opposed to rejecting or accepting specific devices for market use.

Characterization of the trabecular bone structure using frequency modulated ultrasound pulse

The objective of this study was to investigate the efficacy of modulated ultrasound signals in the measurement of bone properties as an early indicator of osteoporosis. Twenty-one trabecular bone cubes were harvested from sheep femoral condyles and the cube axes corresponded to the anatomic superior-inferior (SI), antero-posterior (AP), and medio-lateral (ML) orientations. Micro-CT measurements were made on those samples to obtain bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp). Ultrasound tests were performed in the three orthogonal orientations using pulse and frequency modulated ultrasound. The comparison of the frequency modulated attenuation (FMA) with the broadband ultrasound attenuation (BUA) was made within the frequency band between 300 and 700 kHz. Results showed that FMA demonstrated higher correlations to the trabecular structure properties in the SI orientation (R(2)=0.84 for BV/TV, R(2)=0.77 for Tb.Th, R(2)=0.7 for Tb.Sp) than BUA (R(2)=0.30 for BV/TV, R(2)=0.27 for Tb.Th, R(2)=0.33 for Tb.Sp). In the AP orientation, FMA had higher correlation to Tr.Sp (R(2)=0.64) than BUA (R(2)=0.48), and relatively lower correlation to BV/TV (R(2)=0.48) and Tb.Th (R(2)=0.31) than BUA (R(2)=0.64 for BV/TV and R(2)=0.58 for Tb.Th). The results suggested that FMA could be a new ultrasound index for bone properties assessment.