A two-level subject-specific biomechanical model for improving prediction of hip fracture risk

doi:10.1016/j.clinbiomech.2015.05.013

Clinical Biomechanics

Volume 30, Issue 8, October 2015, Pages 881-887

https://doi.org/10.1016/j.clinbiomech.2015.05.013 Get rights and content

Highlights

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A two-level biomechanical model considers risk factors at both musculoskeletal and femur level;
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The models are constructed subject-specifically by using the subject’s medical images;
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Hip soft tissue is able to greatly attenuate the impact energy and thus reduce the impact force;
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Consistent with clinical observations, high BMI has been found a protective not a risk factor of hip fracture.

Abstract

Background

Sideways fall-induced hip fracture is a major worldwide health problem among the elderly population. However, all existing biomechanical models for predicting hip fracture mainly consider the femur related parameters. Their accuracy is limited as hip fracture is significantly affected by loading conditions as well. The objective of this study was to develop a biomechanical model for improving assessment of hip fracture risk by subject-specific prediction of fall-induced loading conditions.

Method

All information required to construct the models was extracted from the subject's whole-body and hip medical image in order to make the models subject-specific. Fall-induced hip fracture risk for eighty clinical cases was calculated under two sets of loading conditions: subject-specific determined by the proposed model, and non-subject-specific obtained from empirical functions. The predicted hip fracture risk indices were then compared with clinical observations.

Findings

It was found that the subject-specific prediction of fall-induced loading conditions significantly improves the hip fracture risk assessment. Consistent to the clinical observations, the fracture risk predicted by the proposed model suggested that obesity is a protective factor for hip fracture and underweight subjects are more likely to experience a hip fracture.

Interpretations

This study shows that hip fracture risk is affected by a number of factors, including body weight, body height, impact force, body mass index, hip soft tissue thickness, and bone quality. The proposed model provides a comprehensive, fast, accurate, and non-expensive method for prediction of hip fracture risk which should lead to more effective prevention of hip fractures.

Introduction

Hip fracture due to sideways fall is a major health problem over the world (Kannus et al., 2006), as it is associated with significant mortality, disability, and reduced quality of life (Cooper et al., 1992, Cummings and Melton, 2002, Burge et al., 2007, Brauer et al., 2009). Hip fracture can cause approximately 12–20% reduction in expected survival, primarily in the year following the fracture (Magaziner et al., 1989, Wilson et al., 2006). The cost of treating hip fractures and the associated morbidity has significant implications for health care expenditure (Huddleston and Whitford, 2001). Despite the extent of this problem, there is a lack of a subject-specific method for accurate assessment of hip fracture risk. The aim of precisely predicting hip fracture risk is to identify patients at high risk of hip fracture and to start a timely prevention and protection measurement to reduce the incidence of hip fractures.

Various clinical studies have demonstrated that hip fracture is affected by anthropometric parameters, bone quality (Haider et al., 2013), proximal femur anatomy (Gregory and Aspden, 2008, Ito et al., 2010, Carballido-Gamio et al., 2013, Park et al., 2014), cortical thickness (Loveridge et al., 2010, Long et al., 2015), hip soft tissue thickness (STT) (Majumder et al., 2007, Majumder et al., 2008, Majumder et al., 2013), landing surface (Baddoura et al., 2011, Van der Zijden et al., 2012), etc. All these parameters are subject dependent as they vary with gender, race, ethnicity and age (Wang et al., 1994, Peacock et al., 2009, Zhuang et al., 2010). Therefore, hip fracture risk in a sideways fall differs widely from individual to individual, and for one individual from fall to fall. The effective parameters take effect at different scale levels and affect different physical outcomes. For example, body weight (BW), body height (BH), and body configuration take effect at the musculoskeletal level and affect the magnitude of the impact force induced in a sideways fall, while femur bone geometry and local bone density take effect at the organ level (femur bone) and affect the stress distribution in the femur bone. It is very difficult to consider all these parameters within a single-level biomechanical model. The currently available methods for assessing hip fracture risk are of single level and mainly consider the femur-related parameters. For instance, areal bone mineral density (aBMD), measured by DXA (dual energy X-ray absorptiometry) imaging, is used in the evaluation of the femur bone quality to assess the hip fracture risk. aBMD has had limited success in predicting bone strength (McCreadie and Goldstein, 2000). The reason is that BMD does not incorporate other factors that contribute to the bone strength such as bone anatomical geometry and the spatial bone density distribution (Seeman and Delmas, 2006). Therefore, aBMD is not a parameter of sufficient validity to be the sole indicator of fracture risk (Nielsen, 2000). Thus, much attention has been directed towards the HSA (hip structural analysis), subject-specific finite element (FE) analysis, and FRAX (fracture risk assessment tool). One criticism of the available fracture risk indicators has been the lack of consideration of fall related factors (Masud et al., 2011) and loading conditions, which may considerably affect the predicted fracture risk. To our knowledge, there is no published data of a fully subject-specific biomechanical model to accurately consider both loading conditions and femur-related parameters in predicting hip fracture risk.

The objective of the current study was to develop a two-level subject-specific model for improving prediction of hip fracture risk. The introduced dynamics model by the authors in Luo et al. (2014a) and Nasiri Sarvi et al. (2014) was improved in this study to be able to consider the subject-specific effect of hip soft tissues in attenuating the impact energy and to predict the applied joint force to the femoral head. In order to evaluate the effect of loading condition on hip fracture risk assessment, fracture risk indices (FRI) were calculated for eighty clinical cases under two sets of loading conditions, subject-specific and non-subject-specific, and results were compared with clinical observations.

Section snippets

Methods

The proposed two-level biomechanical model consists of a whole-body dynamics model and a proximal-femur FE model. The whole-body dynamics model was used to predict the lateral fall-induced loading condition onto the femur. Determined load/constraint conditions were then applied in the proximal-femur finite element model to calculate the stresses in the femur bone. Subject's whole-body and hip DXA scans were used to construct the models. The procedure of constructing the two-level biomechanical

Impact force

Predicted impact and joint forces time histories by the subject-specific model had different patterns for different subjects in terms of the peak magnitude and the time to the peak value. However, the configuration and direction of the impact and the joint forces ensured that they are respectively applied to the greater trochanter and the femoral head for all cases which is consistent with the implemented subject-specific boundary conditions (Figs. C1 and E1(a) in the Supplementary Material).

Conclusion

To improve the accuracy of predicting sideways fall-induced hip fracture risk, this paper presented a two-level subject-specific biomechanical model constructed from the subject's whole-body and hip DXA images. The model considered both fall- and femur-related parameters in the hip fracture risk assessment. The effect of considering subject-specific loading conditions was examined on fracture risk prediction of eighty clinical cases. It could be concluded that subject-specific consideration of

Acknowledgment

The reported research has been supported by the Natural Sciences and Engineering Council (NSERC) (37098) and the Manitoba Health Research Council (MHRC) (37807) in Canada, which are gratefully acknowledged.

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Subject-specific ex vivo simulations for hip fracture risk assessment in sideways falls
2019, Bone
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.
Improving the prediction of sideways fall-induced impact force for women by developing a female-specific equation
2019, Journal of Biomechanics
Citation Excerpt :
The model considered the effective parameters on the applied force to the hip, including body anthropometric parameters (body segments mass, length, mass center, and mass moment of inertia), body segments kinematics during the fall, and the sex-specific effect of GT soft tissues in attenuating the impact force. Construction of the model is described in detail elsewhere (Luo et al., 2014; Nasiri Sarvi and Luo, 2015; Nasiri Sarvi et al., 2014). In short, body falling was divided to two phases and each phase was simulated by a separate model:
Impact force induced in sideways falls is an important determinant of hip fracture risk. While body parameters may differently affect the magnitude of impact force in men and women, the effect of sex is not considered in existing impact force predictors. The objective of this study was to construct a female-specific equation to predict the fall-induced impact force applied to the hip and evaluate whether it could improve hip facture risk assessment.
A previously developed human-body dynamic model was used to simulate falling of 80 women and determine the hip impact force. Results were then used to derive a female-specific equation between impact force and body parameters. The proposed female-specific equation and available non-sex-specific impact force predictors in the literature were integrated with a finite element model to discriminate hip fracture patients among 393 women (99 hip fractures; 294 non-fracture controls). Results of the implemented methods were compared to evaluate whether considering the effect of sex could improve the discrimination of females with and without a hip fracture.
The area under the curve (AUC) and odds ratio (OR) for the assessed hip fracture risk by the proposed female-specific method (AUC = 0.799, OR = 4.22) were significantly ( $p < 0.001)$ greater than those of non-sex-specific methods (the most accurate: AUC  $= 0.750$ , OR  $= 3.62$ ). This study indicates that the proposed equation may be useful to improve hip fracture risk assessment for women.
The influence of muscle activation on impact dynamics during lateral falls on the hip
2018, Journal of Biomechanics
Citation Excerpt :
While the current results demonstrate that muscle activation increases during the time-course of a lateral pelvis impact, and that pre-activation increases the magnitude and rate of external loads during the impact phase of a sideways fall, they do not necessarily suggest that muscle activation increases hip fracture risk. In contrast, while Chang et al. report that muscle activation during front car collisions increases external loads applied at the knee, they found that, due to the bending moments that the muscles apply, the risk of hip fracture decreases (while the risk of femur shaft fractures increases) (Chang et al., 2009; Sarvi and Luo, 2015). Similarly, Choi et al. report that contraction of the hip abductor muscles at the moment of impact substantially reduced peak compressive and tensile stresses at the femoral neck and risk for femoral fracture during a sideways fall (Choi et al., 2014).
Muscle activation has been demonstrated to influence impact dynamics during scenarios including running, automotive impacts, and head impacts. This study investigated the effects of targeted muscle activation magnitude on impact dynamics during low energy falls on the hip with human volunteers. Fifteen university-aged participants (eight females, seven males) underwent 12 lateral pelvis release trials. Half of the trials were muscle-‘relaxed’; in the remaining ‘contracted’ trials participants isometrically contracted their gluteus medius to 20–30% of maximal voluntary contraction before the drop was initiated onto a force plate. Peak force applied to the femur-pelvis complex averaged 9.3% higher in contracted compared to relaxed trials (F = 6.798, p = .022). Muscle activation effects were greater for females, resulting in (on average) an 18.5% increase in effective pelvic stiffness (F = 5.838, p = .046) and a 23.4% decrease in time-to-peak-force (F = 5.109, p = .042). In the relaxed trials, muscle activation naturally increased during the impact event, reaching levels of 12.8, 7.5, 11.1, and 19.1% MVC at the time of peak force for the gluteus medias, vastus lateralis, erector spinae, and external oblique, respectively. These findings demonstrated that contraction of trunk and hip musculature increased peak impact force across sexes. In females, increases in the magnitude and rate of loading were accompanied (and likely driven) by increases in system stiffness. Accordingly, incorporating muscle activation contributions into biomechanical models that investigate loading dynamics in the femur and/or pelvis during lateral impacts may improve estimate accuracy.
Comparison of non-invasive assessments of strength of the proximal femur
2017, Bone
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 ± 8.8 years), 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 = 896 N, 95%CI 830–961) significantly better than femoral neck aBMD by DXA (R²_adj = 0.69, 95%CI 0.66–0.72; RMSE = 1011 N, 95%CI 952–1069) and the QCT-based model (R²_adj = 0.73, 95%CI 0.71–0.75; RMSE = 932 N, 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.
Study of sex differences in the association between hip fracture risk and body parameters by DXA-based biomechanical modeling
2016, Bone
Citation Excerpt :
The impact model was used to determine the time history of the impact force applied from the ground to the greater trochanter. The impulse-momentum principle was also used to determine the joint force applied from the acetabulum to the femoral head in a sideways fall [59]. The determined fall-induced load/constraint conditions were then applied to the proximal femur finite element (FE) model (Fig. 1(d)) to calculate the stress/strain distribution in the femur bone.
There is controversy about whether or not body parameters affect hip fracture in men and women in the same way. In addition, although bone mineral density (BMD) is currently the most important single discriminator of hip fracture, it is unclear if BMD alone is equally effective for men and women. The objective of this study was to quantify and compare the associations of hip fracture risk with BMD and body parameters in men and women using our recently developed two-level biomechanical model that combines a whole-body dynamics model with a proximal-femur finite element model. Sideways fall induced impact force of 130 Chinese clinical cases, including 50 males and 80 females, were determined by subject-specific dynamics modeling. Then, a DXA-based finite element model was used to simulate the femur bone under the fall-induced loading conditions and calculate the hip fracture risk. Body weight, body height, body mass index, trochanteric soft tissue thickness, and hip bone mineral density were determined for each subject and their associations with impact force and hip fracture risk were quantified. Results showed that the association between impact force and hip fracture risk was not strong enough in both men (r = − 0.31 , p < 0.05) and women (r = 0.42 , p < 0.001) to consider the force as a sole indicator of hip fracture risk. The correlation between hip BMD and hip fracture risk in men (r = − 0.83 , p < 0.001) was notably stronger than that in women (r = − 0.68 , p < 0.001). Increased body mass index was not a protective factor against hip fracture in men (r = − 0.13 , p > 0.05), but it can be considered as a protective factor among women (r = − 0.28 , p < 0.05). In contrast to men, trochanteric soft tissue thickness can be considered as a protective factor against hip fracture in women (r = − 0.50 , p < 0.001). This study suggested that the biomechanical risk/protective factors for hip fracture are sex-specific. Therefore, the effect of body parameters should be considered differently for men and women in hip fracture risk assessment tools. These findings support further exploration of sex-specific preventive and protective measurements to reduce the incidence of hip fractures.
Modelling Human-Structure Interaction in Sideways Fall for Hip Impact Force Estimation
2022, International Journal of Technology

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A two-level subject-specific biomechanical model for improving prediction of hip fracture risk

Highlights

Abstract

Background

Method

Findings

Interpretations

Introduction

Section snippets

Methods

Impact force

Conclusion

Acknowledgment

J. Clin. Densitom.

Eur. J. Radiol.

J. Biomech.

Bone

Lancet

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Mayo Clin. Proc.

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Bone Rep.

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