Sideways Fall Research Articles

The effect of body configuration on the strain magnitude and distribution within the acetabulum during sideways falls: A finite element approach

While the incidence of hip fractures has declined during the last decades, the incidence of acetabular fractures resulting from low-energy sideways falls has increased, and the mechanisms responsible for this trend remain unknown. Previous studies have suggested that body configuration during the impact plays an important role in a hip fracture. Thus, the aim of this study was to investigate the effect of body configuration angles (trunk tilt angle, trunk flexion angle, femur horizontal rotation angle, and femur diaphysis angle) on low-energy acetabular fractures via a parametric analysis. A computed tomography–based (CT) finite element model of the ground–proximal femur–pelvis complex was created, and strain magnitude, time-history response, and distribution within the acetabulum were evaluated. Results showed that while the trunk tilt angle and femur diaphysis angle have the greatest effect on strain magnitude, the direction of the fall (lateral vs. posterolateral) contributes to strain distribution within the acetabulum. The results also suggest that strain level and distribution within the proximal femur and acetabulum resulting from a sideways fall are not similar and, in some cases, even opposite. Taken together, our simulations suggest that a more horizontal trunk and femoral shaft at the impact phase can increase the risk of low-energy acetabular fractures.

Periprosthetic femoral fractures in sideways fall configuration: comparative numerical analysis of the influence of femoral stem design.

The aim of this study was to investigate the mechanisms of periprosthetic fractures occurring as a result of a sideways fall in total hip arthroplasty patients, and to compare the predictions of numerical models in terms of load distribution on the implanted femur with clinical data. 3 numerical models were built: 1 for intact femur and 2 for implanted femur with a straight stem (resembling PBF, Permedica) and with an anatomical stem (resembling ABG II, Stryker). 4 loading configurations were simulated; 1 simulates a vertical load, and 3 simulate a fall with impact on the greater trochanter in different directions. Stress state calculated in the implanted femur was compared for the 2 models with reference to the intact case. These were compared with clinical data collected at a single centre (Istituto Ortopedico Gaetano Pini, Milan, Italy) where 41 patients were investigated after periprosthetic fracture: 26 patients had a straight uncemented stem and 15 an anatomical uncemented stem. The maximum calculated strain in compression in the case of ABG II implanted femur was 2 times higher than in the presence of PBF stem in the vertical loading configuration. For configurations of sideways fall, in both models, there was a progressive increase of stress state in the bone with increasing angle. Simulations of sideways fall elicited results in accordance with clinical observations: due to the peculiar stem design and consequent state of stress in the bone, anatomical stems seem to induce trochanteric fractures more frequently, while for straight stems type B fractures are more likely to occur. Clinical findings confirmed numerical model predictions: stem design seems to highly influence distribution of stress in the bone and consequent localisation of the fracture site.

Force attenuation properties of shear-thickening polymer (STP)-based hip protector in simulated sideways fall

Shear-thickening polymer (STP) has a unique property of increasing its viscosity with an increase in shear strain to attenuate the application of force, implying that it can be used as a material for hip protectors. This study introduces a new hip protector composed of STP and compares its force attenuation capacity to that of other commercial hip protectors in simulated sideways falls. The performance of the STP-based hip protector was analyzed against eight commercial hip protectors (Pelican, Posey, SafeHip, Hornsby, FallSafe, HipSaver, Impact Wear (Hard), Impact Wear (Soft)). The simulated sideways fall conditions were created by a drop weight impact testing system using an anatomical hip model. The machine was dropped from a 20 or 30 cm height resulting in impact energy of 25.1 J (low) or 44.1 J (moderate), respectively. At low impact energy, the commercial hip protectors showed an attenuation range from 21.6 % to 53.3 %, and the STP-based hip pad was able to attenuate the force by 42.7 %. At moderate impact energy, the commercial hip protectors showed an attenuation range from 23 % to 54.3 %, and the STP-based hip pad was able to attenuate the force by 32.6 %. The low coefficient of variance showed a high precision in the execution of the experiments. Although the STP-based hip protector was thinner than the average of commercial soft shell pads and retained comfortable fit, it showed comparable force attenuation capacity to the commercial ones for the low impact energy test. This study highlights that STP, in combination with a polyurethane foam layer, provides the best features in energy-absorption and shunting, showing that it can be used in hip protectors to gain a competitive advantage over others.

MRI-derived porosity index is associated with whole-bone stiffness and mineral density in human cadaveric femora.

Ultrashort echo time (UTE) magnetic resonance imaging (MRI) measures proton signals in cortical bone from two distinct water pools, bound water, or water that is tightly bound to bone matrix, and pore water, or water that is freely moving in the pore spaces in bone. By isolating the signal contribution from the pore water pool, UTE biomarkers can directly quantify cortical bone porosity in vivo. The Porosity Index (PI) is one non-invasive, clinically viable UTE-derived technique that has shown strong associations in the tibia with μCT porosity and other UTE measures of bone water. However, the efficacy of the PI biomarker has never been examined in the proximal femur, which is the site of the most catastrophic osteoporotic fractures. Additionally, the loads experienced during a sideways fall are complex and the femoral neck is difficult to image with UTE, so the usefulness of the PI in the femur was unknown. Therefore, the aim of this study was to examine the relationships between the PI measure in the proximal cortical shaft of human cadaveric femora specimens compared to (1) QCT-derived bone mineral density (BMD) and (2) whole bone stiffness obtained from mechanical testing mimicking a sideways fall. Fifteen fresh, frozen whole cadaveric femora specimens (age 72.1±15.0years old, 10 male, 5 female) were scanned on a clinical 3-T MRI using a dual-echo UTE sequence. Specimens were then scanned on a clinical CT scanner to measure volumetric BMD (vBMD) and then non-destructively mechanically tested in a sideways fall configuration. The PI in the cortical shaft demonstrated strong correlations with bone stiffness (r=-0.82, P=0.0014), CT-derived vBMD (r=-0.64, P=0.0149), and with average cortical thickness (r=-0.60, P=0.0180). Furthermore, a hierarchical regression showed that PI was a strong predictor of bone stiffness which was independent of the other parameters. The findings from this study validate the MRI-derived porosity index as a useful measure of whole-bone mechanical integrity and stiffness.

Body Anthropometry and Bone Strength Conjointly Determine the Risk of Hip Fracture in a Sideways Fall

We hypothesize that variations of body anthropometry, conjointly with the bone strength, determine the risk of hip fracture. To test the hypothesis, we compared, in a simulated sideways fall, the hip impact energy to the energy needed to fracture the femur. Ten femurs from elderly donors were tested using a novel drop-tower protocol for replicating the hip fracture dynamics during a fall on the side. The impact energy was varied for each femur according to the donor’s body weight, height and soft-tissue thickness, by adjusting the drop height and mass. The fracture pattern, force, energy, strain in the superior femoral neck, bone morphology and microarchitecture were evaluated. Fracture patterns were consistent with clinically relevant hip fractures, and the superior neck strains and timings were comparable with the literature. The hip impact energy (11 – 95 J) and the fracture energy (11 – 39 J) ranges overlapped and showed comparable variance (CV = 69 and 61%, respectively). The aBMD-based definition of osteoporosis correctly classified 7 (70%) fracture/non-fracture cases. The incorrectly classified cases presented large impact energy variations, morphology variations and large subcortical voids as seen in microcomputed tomography. In conclusion, the risk of osteoporotic hip fracture in a sideways fall depends on both body anthropometry and bone strength.

In Vivo Assessment of Age- and Loading Configuration-Related Changes in Multiscale Mechanical Behavior of the Human Proximal Femur Using MRI-Based Finite Element Analysis.

MRI-based finite element analysis (MRI-FEA) is the only method able to assess microstructural and whole-bone mechanical properties of the hip in vivo. To examine whether MRI-FEA is capable of discriminating age-related changes in whole-bone mechanical performance and micromechanical behavior of the proximal femur, particularly considering the most common hip fracture-related sideways fall loading. Retrospective. A total of nine younger (27 ± 3.2 years) and nine elderly (61 ± 3.9 years) healthy volunteers. 3T; 3D fast field echo sequence. The left proximal femurs were scanned and FE models created. FEA was performed to simulate sideways fall and stance loading for each femoral model. Apparent stiffness and high-risk (90th percentile) tensile and compressive strains of the proximal femur as well as the average strains within cubic regions of the femoral neck and greater trochanter were assessed. Paired and unpaired t-tests. Compared to the young group, the femoral stiffness of the elderly decreased by 39% and 40% (both P < 0.05) under the sideways fall and stance conditions, respectively. Accordingly, the high-risk tensile and compressive stains were elevated with aging (40% and 23% for sideways fall, 23% and 11% for stance conditions; all P < 0.05). However, the loading configuration-induced difference was only observed in the elderly group for the high-risk strains (22% for tension and 12% for compression; both P < 0.05). Additionally, compared to the stance condition, the sideways fall increased the average tensile (young: 108%, elderly: 123%; both P < 0.05) and compressive strains (young: 631%, elderly: 617%, both P < 0.05) within the greater trochanter rather than the femoral neck region. In vivo MRI-FEA is capable of capturing age-related changes in both apparent-level stiffness and tissue-level micromechanical behavior of the proximal femur. However, the effect of sideways fall loading might be better reflected by tissue-level micromechanics rather than apparent stiffness. 3 TECHNICAL EFFICACY STAGE: 1.

Validation of 3D finite element models from simulated DXA images for biofidelic simulations of sideways fall impact to the hip.

Computed tomography (CT)-derived finite element (FE) models have been proposed as a tool to improve the current clinical assessment of osteoporosis and personalized hip fracture risk by providing an accurate estimate of femoral strength. However, this solution has two main drawbacks, namely: (i) 3D CT images are needed, whereas 2D dual-energy x-ray absorptiometry (DXA) images are more generally available, and (ii) quasi-static femoral strength is predicted as a surrogate for fracture risk, instead of predicting whether a fall would result in a fracture or not. The aim of this study was to combine a biofidelic fall simulation technique, based on 3D computed tomography (CT) data with an algorithm that reconstructs 3D femoral shape and BMD distribution from a 2D DXA image. This approach was evaluated on 11 pelvis-femur constructs for which CT scans, ex vivo sideways fall impact experiments and CT-derived biofidelic FE models were available. Simulated DXA images were used to reconstruct the 3D shape and bone mineral density (BMD) distribution of the left femurs by registering a projection of a statistical shape and appearance model with a genetic optimization algorithm. The 2D-to-3D reconstructed femurs were meshed, and the resulting FE models inserted into a biofidelic FE modeling pipeline for simulating a sideways fall. The median 2D-to-3D reconstruction error was 1.02mm for the shape and 0.06g/cm3 for BMD for the 11 specimens. FE models derived from simulated DXAs predicted the outcome of the falls in terms of fracture versus non-fracture with the same accuracy as the CT-derived FE models. This study represents a milestone towards improved assessment of hip fracture risk based on widely available clinical DXA images.

Effect of Femur Geometry on Hip Protectors Testing System

There have been different types of simplified femoral geometry incorporated into test systems for testing the biomechanical effectiveness of hip protectors. However, the effect of the simplification of femoral geometry in simulated sideways impact experiment has not been reported. In this study, an actual femoral geometry was fabricated and examined along with a simplified femoral geometry in a surrogate hip arrangement to mimic the fracture-causing situation in a sideways fall. A pendulum impact testing machine was used to evaluate the impact force response of both the femoral geometries at various velocity and constant residual impact energy for both geometries. The result showed that the peak impact force varied only 9% between actual and simplified geometries after normalizing the weight for both femurs in testing without a hip protector. However, a higher distinction of the impact force responses of both femurs was observed when testing with a hip protector. This findings at this moment suggest that the femur geometry affects the performance of a testing system. Therefore, the simplified femur geometry may not accurately substitute for the actual femur geometry in comparison of the impact attenuation of a hip protector in a simulated sideways fall.

MRI-based assessment of proximal femur strength compared to mechanical testing.

Half of the women who sustain a hip fracture would not qualify for osteoporosis treatment based on current DXA-estimated bone mineral density criteria. Therefore, a better approach is needed to determine if an individual is at risk of hip fracture from a fall. The objective of this study was to determine the association between radiation-free MRI-derived bone strength and strain simulations compared to results from direct mechanical testing of cadaveric femora. Imaging was conducted on a 3-Tesla MRI scanner using two sequences: one balanced steady-state free precession sequence with 300μm isotropic voxel size and one spoiled gradient echo with anisotropic voxel size of 234×234×1500μm. Femora were dissected free of soft-tissue and 4350-ohm strain-gauges were securely applied to surfaces at the femoral shaft, inferior neck, greater trochanter, and superior neck. Cadavers were mechanically tested with a hydraulic universal test frame to simulate loading in a sideways fall orientation. Sideways fall forces were simulated on MRI-based finite element meshes and bone stiffness, failure force, and force for plastic deformation were computed. Simulated bone strength metrics from the 300μm isotropic sequence showed strong agreement with experimentally obtained values of bone strength, with stiffness (r=0.88, p=0.0002), plastic deformation point (r=0.89, p<0.0001), and failure force (r=0.92, p<0.0001). The anisotropic sequence showed similar trends for stiffness, plastic deformation point, and failure force (r=0.68, 0.70, 0.84; p=0.02, 0.01, 0.0006, respectively). Surface strain-gauge measurements showed moderate to strong agreement with simulated magnitude strain values at the greater trochanter, superior neck, and inferior neck (r=-0.97, -0.86, 0.80; p≤0.0001, 0.003, 0.03, respectively). The findings from this study support the use of MRI-based FE analysis of the hip to reliably predict the mechanical competence of the human femur in clinical settings.

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

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. 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. 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. 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.

Influence of hip geometry to intracapsular fractures in Sri Lankan women: prediction of country specific values

Falls are very common in daily life. Hip is a highly vulnerable location during a fall. Trochanter can be compressed due to side falls resulting either intracapsular or extracapsular fracture. The relationship of bone geometry to the fracture risk can be analysed as a determinant of mechanical resistance of the bone, as well as a promising fracture prediction tool. Intracapsular fractures are highly depend on the hip geometry compared to the extracapsular fractures. This study aims to find out the influence of hip geometry to the intracapsular fractures among Sri Lankan women. Hip axis length (HAL), neck shaft angle (NSA), femoral neck width (FNW) and moment arm length of intracapsular patients have compared with a normal group. Concurrently, the moment applied to the proximal femur during the sideway fall is computed and compared with a normal group. We observed that fractured group has greater NSA, HAL and FNW compared to the normal group. Furthermore, intracapsular fracture females have longer moment arm of the force in the sideway fall resulting a greater load on femoral neck compared to the normal group.

Influence of hip geometry to intracapsular fractures in Sri Lankan women: prediction of country specific values

Falls are very common in daily life. Hip is a highly vulnerable location during a fall. Trochanter can be compressed due to side falls resulting either intracapsular or extracapsular fracture. The relationship of bone geometry to the fracture risk can be analysed as a determinant of mechanical resistance of the bone, as well as a promising fracture prediction tool. Intracapsular fractures are highly depend on the hip geometry compared to the extracapsular fractures. This study aims to find out the influence of hip geometry to the intracapsular fractures among Sri Lankan women. Hip axis length (HAL), neck shaft angle (NSA), femoral neck width (FNW) and moment arm length of intracapsular patients have compared with a normal group. Concurrently, the moment applied to the proximal femur during the sideway fall is computed and compared with a normal group. We observed that fractured group has greater NSA, HAL and FNW compared to the normal group. Furthermore, intracapsular fracture females have longer moment arm of the force in the sideway fall resulting a greater load on femoral neck compared to the normal group.

Comparing the fracture limits of the proximal femur under impact and quasi-static conditions in simulation of a sideways fall

Sideways falls onto the hip are responsible for a great number of fractures in older adults. One of the possible ways to prevent these fractures is through early identification of people at greatest risk so that preventive measures can be properly implemented. Many numerical techniques that are designed to predict the femur fracture risk are validated through performing quasi-static (QS) mechanical tests on isolated cadaveric femurs, whereas the real hip fracture is a result of an impact (IM) incident. The goal of this study was to compare the fracture limits of the proximal femur under IM and QS conditions in the simulation of a sideways fall to identify any possible relationship between them.Eight pairs of fresh frozen cadaveric femurs were divided into two groups of QS and IM (left and right randomized). All femurs were scanned with a Hologic DXA scanner and then cut and potted in a cylindrical tube. To measure the stiffness in two conditions of the single-leg stance (SLS) and sideways fall (SWF), non-destructive tests at a QS displacement rate were performed on the two groups. For the destructive tests, the QS group was tested in SWF configuration with the rate of 0.017 mm/s using a material testing machine, and the IM group was tested in the same configuration inside a pneumatic IM device with the projectile target displacement rate of 3 m/s.One of the IM specimens was excluded due to multiple strikes. The result of this study showed that there were no significant differences in the SLS and SWF stiffnesses between the two groups (P = 0.15 and P = 0.64, respectively). The destructive test results indicated that there was a significant difference in the fracture loads of the two groups (P < 0.00001) with the impact ones being higher; however, they were moderately correlated (R2 = 0.45). Also, the comparison of the fracture location showed a qualitatively good agreement between the two groups.Using the relationship developed herein, results from another study were extrapolated with errors of less than 12%, showing that meaningful predictions for the impact scenario can be made based on the quasi-static tests. The result of this study suggests that there is a potential to replace IM tests with QS displacement rate tests, and this will provide important information that can be used for future studies evaluating clinical factors related to fracture risk.

COMPARATIVE STUDY OF THREE DIFFERENT PREGNANCY DIAGNOSIS TECHNIQUES IN RABBITS

Seven pluriparous non-gravid does and two matured bucks were utilized for the study. Does were all mated after 30 days of stabilization. Successful mating was confirmed by a recoil, backward or sideway fall and emission of a snorting sound by the male. Pregnancy detection was by weight gain, abdominal palpation and ultrasonography techniques at days 6, 9,13,18,23. Abdominal palpation of does was carried out by gentle palpation of nodule-like tissues in the ventral abdomen. Transcutaneous ultrasonography was performed using ultrasound machine Kaixin KX2000®. Weight gain was monitored using a sensitive weighing scale. Early pregnancy was diagnosed by ultrasonography and abdominal palpation on days 6.00±0.00 and 7.5±1.29 post-copulation respectively. Pregnancy was diagnosed by abdominal palpation in 28.57% of the does on day 6 and increased to 100% on day 9 post-copulation; however diagnosis by ultrasonography was 100% on day 6. The average weight gain was 0.029±0.029kg by day 6; 0.057±0.4 by day 13, which plateaued till parturition. Ultrasonography could therefore be used effectively for pregnancy diagnosis as early as day 6 of gestation in rabbit does while abdominal palpation could serve in absence of ultrasonography by day 9 of gestation. Weight gain is a positive adjunct to other pregnancy diagnostic techniques.&#x0D; &#x0D; &#x0D;

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.

Age-Related Differences in Head Impact during Experimentally Induced Sideways Falls.

Purpose To examine head impact incidence and head acceleration during experimentally induced falls as a function of age. Methods 15 young adults (21.2±2.7) and 10 older adults (61.9±4.3 years) underwent 6 experimentally induced sideways falls. Participants fell sideways onto a 20cm crash pad. The number of head impacts was tabulated from video recordings and head acceleration was calculated from motion capture data. A total of 147 falls were analyzed. Results The young group underwent 88 falls, in which 11.4% resulted in head impact. The older group underwent 59 falls, in which 34.5% resulted in head impact. A proportion analysis revealed older adults had a significantly greater proportion of head impacts than young adults (X2(1) = 11.445, p = 0.001). A two-way ANOVA only revealed a main effect of head impact on acceleration (F(1,142) = 54.342, p<0.001). Conclusion The older adults experienced a greater proportion of head impacts during sideways falls. Head impact resulted in greater head acceleration compared to no head impact. Collectively, this data highlights the possibility that age-related neuromuscular changes to head control may result in elevated risk of fall-related TBIs. Future research examining mechanisms underlying increases in fall-related head impact is warranted.

In vitro injection of osteoporotic cadaveric femurs with a triphasic calcium-based implant confers immediate biomechanical integrity.

ABSTRACTCurrent pharmaceutical therapies can reduce hip fractures by up to 50%, but compliance to treatment is low and therapies take up to 18 months to reduce risk. Thus, alternative or complementary approaches to reduce the risk of hip fracture are needed. The AGN1 local osteo‐enhancement procedure (LOEP) is one such alternative approach, as it is designed to locally replace bone lost due to osteoporosis and provide immediate biomechanical benefit. This in vitro study evaluated the initial biomechanical impact of this treatment on human cadaveric femurs. We obtained 45 pairs of cadaveric femurs from women aged 77.8 ± 8.8 years. One femur of each pair was treated, while the contralateral femur served as an untreated control. Treatment included debridement, irrigation/suction, and injection of a triphasic calcium‐based implant (AGN1). Mechanical testing of the femora was performed in a sideways fall configuration 24 h after treatment. Of the 45 pairs, 4 had normal, 16 osteopenic, and 25 osteoporotic BMD T‐scores. Altogether, treatment increased failure load on average by 20.5% (p < 0.0001). In the subset of osteoporotic femurs, treatment increased failure load by 26% and work to failure by 45% (p < 0.01 for both). Treatment did not significantly affect stiffness in any group. These findings provide evidence that local delivery of the triphasic calcium‐based implant in the proximal femur is technically feasible and provides immediate biomechanical benefit. Our results provide strong rationale for additional studies investigating the utility of this approach for reducing the risk of hip fracture. © 2019 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society.

Assessment of hip fracture risk by cross-sectional strain-energy derived from image-based beam model

BackgroundClinicians have been looking for a simple and effective biomechanical tool for the assessment of hip fracture risk. Dual-energy X-ray absorptiometry (DXA) is currently the primary bone imaging modality in clinic, and the engineering beam is the simplest model for a mechanical analysis. Therefore, we developed a DXA-based beam model for the above purpose. MethodsA beam model of the proximal femur was constructed from the subject's hip DXA image and denoted DXA-beam. Femur stiffness was calculated at cross-sections of interest using areal bone-mineral-density profile. Impact force induced in a sideways fall was applied as a critical loading. Fracture risk index at a cross-section was defined as the ratio of strain-energy induced by the impact force to the allowable strain-energy. A clinic cohort was used to study the discriminability of DXA-beam, which was measured by the area under the curve and odds ratio, both with 95% confidential interval. FindingsFracture risk measured by DXA-beam model at the femoral neck [odds ratio 2.23, 95% confidence interval (1.83, 2.57)], inter-trochanter [2.49, (2.14, 3.25)] and sub-trochanter [2.82, (2.38, 3.51)] were strongly associated with hip fracture. The area under the curve by DXA-beam at the femoral neck [0.74, 95% confidence interval (0.70, 0.76)], inter-trochanter [0.77, (0.75, 0.82)] and sub-trochanter [0.76, (0.74, 0.81)] were higher than that by femoral neck bone mineral density [0.71, (0.65, 0.78)]. InterpretationThe DXA-beam model is a simple and yet effective mechanical model. It had promising performance in discrimination of fracture cases from controls.

Fracture Risk Indices From DXA-Based Finite Element Analysis Predict Incident Fractures Independently From FRAX: The Manitoba BMD Registry

Objective: Finite element analysis (FEA) is a computational method to predict the behavior of materials under applied loading. We developed a software tool that automatically performs FEA on dual-energy X-ray absorptiometry hip scans to generate site-specific fracture risk indices (FRIs) that reflect the likelihood of hip fracture from a sideways fall. This longitudinal study examined associations between FRIs and incident fractures. Methods: Using the Manitoba Bone Mineral Density (BMD) Registry, femoral neck (FN), intertrochanter (IT), and subtrochanter (ST) FRIs were automatically derived from 13,978 anonymized dual-energy X-ray absorptiometry scans (Prodigy, GE Healthcare) in women and men aged 50 yr or older (mean age 65 yr). Baseline covariates and incident fractures were assessed from population-based data. We compared c-statistics for FRIs vs FN BMD alone and fracture risk assessment (FRAX) probability computed with BMD. Cox regression was used to estimate hazard ratios and 95% confidence intervals (95% CIs) for incident hip, major osteoporotic fracture (MOF) and non-hip MOF adjusted for relevant covariates including age, sex, FN BMD, FRAX probability, FRAX risk factors, and hip axis length (HAL). Results: During mean follow-up of 6 yr, there were 268 subjects with incident hip fractures, 1003 with incident MOF, and 787 with incident non-hip MOF. All FRIs gave significant stratification for hip fracture (c-statistics FN-FRI: 0.76, 95% CI 0.73–0.79, IT-FRI 0.74, 0.71–0.77; ST-FRI 0.72, 0.69–0.75). FRIs continued to predict hip fracture risk even after adjustment for age and sex (hazard ratio per standard deviation FN-FRI 1.89, 95% CI 1.66–2.16); age, sex, and BMD (1.26, 1.07–1.48); FRAX probability (1.30, 1.11–1.52); FRAX probability with HAL (1.26, 1.05–1.51); and individual FRAX risk factors (1.32, 1.09–1.59). FRIs also predicted MOF and non-hip MOF, but the prediction was not as strong as for hip fracture. Summary: Automatically-derived FN, IT, and ST FRIs are associated with incident hip fracture independent of multiple covariates, including FN BMD, FRAX probability and risk factors, and HAL.

Femoral Fracture load and damage localization pattern prediction based on a quasi-brittle law

Finite element analysis is one of the most used tools for studying femoral neck fracture. Nerveless, consensus concerning either the choice of material characteristics, damage law and /or geometric models (linear on nonlinear) remains unreached. In this work, we propose a numerical quasi-brittle damage model to describe the behavior of the proximal femur associated with two methods to evaluate the Young modulus. Eight proximal femur finite elements models were constructed from CT scan data (4 donors: 3 women; 1 man). The numerical computations showed a good agreement between the numerical curves (load – displacement) and the experimental ones. A very encouraging result is obtained when a comparison is made between the computed fracture loads and the experimental ones (R2=0.825, Relative error =6.49%). All specific numerical computation provided very fair qualitative matches with the fracture patterns for the sideway fall simulation. Finally, the comparative study based on 32 simulations adopting linear and nonlinear meshing led to the conclusion that the quantitatively results are improved when a nonlinear mesh is used.