Trochanteric Soft Tissue Research Articles

Force magnitude and distribution during impacts to the hip are affected differentially by body size and body composition

Hip fractures are a severe health concern among older adults. While anthropometric factors have been shown to influence hip fracture risk, the low fidelity of common body composition metrics (e.g. body mass index) reduces our ability to infer underlying mechanisms. While simulation approaches can be used to explore how body composition influences impact dynamics, there is value in experimental data with human volunteers to support the advancement of computational modeling efforts. Accordingly, the goal of this study was to use a novel combination of subject-specific clinical imaging and laboratory-based impact paradigms to assess potential relationships between high-fidelity body composition and impact dynamics metrics (including load magnitude and distribution and pelvis deflection) during sideways falls on the hip in human volunteers.Nineteen females (<35 years) participated. Body composition was assessed via DXA and ultrasound. Participants underwent low-energy (but clinically relevant) sideways falls on the hip during which impact kinetics (total peak force, contract area, peak pressure) and pelvis deformation were measured. Pearson correlations assessed potential relationships between body composition and impact characteristics.Peak force was more strongly correlated with total mass (r = 0.712) and lean mass indices (r = 0.510–0.713) than fat mass indices (r = 0.401–0.592). Peak deflection was positively correlated with indices of adiposity (all r > 0.7), but not of lean mass. Contact area and peak pressure were positively and negatively associated, respectively, with indices of adiposity (all r > 0.49). Trochanteric soft tissue thickness predicted 59 % of the variance in both variables, and was the single strongest correlate with peak pressure. In five-of-eight comparisons, hip-local (vs. whole body) anthropometrics were more highly associated with impact dynamics.In summary, fall-related impact dynamics were strongly associated with body composition, providing support for subject-specific lateral pelvis load prediction models that incorporate soft tissue characteristics. Integrating soft and skeletal tissue properties may have important implications for improving the biomechanical effectiveness of engineering-based protective products.

Finite element analysis of hip fracture risk in elderly female: The effects of soft tissue shape, fall direction, and interventions

This study investigates the effects of fall configurations on hip fracture risk with a focus on pelvic soft tissue shape. This was done by employing a whole-body finite element (FE) model. Soft tissue thickness around the pelvis was measured using a standing CT system, revealing a trend of increased trochanteric soft tissue thickness with higher BMI and younger age. In the lateroposterior region from the greater trochanter, the soft tissues of elderly females were thin with a concave shape. Based on the THUMS 5F model, an elderly female FE model with a low BMI was developed by morphing the soft tissue shape around the pelvis based on the CT data. FE simulation results indicated that the lateroposterior fall led to a higher femoral neck force for the elderly female model compared to the lateral fall. One reason may be related to the thin soft tissue of the pelvis in the lateroposterior region. Additionally, the effectiveness of interventions that can help mitigating hip fractures in lateroposterior falls on the thigh-hip and hip region was assessed using the elderly female model. The attenuation rate of the femoral neck force by the hip protector was close to zero in the thigh-hip fall and high in the hip fall, whereas the attenuation rate of the compliant floor was high in both falls. This study highlights age-related changes in the soft tissue shape of the pelvis in females, particularly in the lateroposterior regions, which may influence force mitigation for the hip joint during lateroposterior falls.

Effects of hip muscle activation on the stiffness and energy absorption of the trochanteric soft tissue during impact in sideways falls

The trochanteric soft tissue attenuates impact force or absorbs impact energy during a fall on the hip (thereby helps to reduce a risk of hip fracture). While the benefits should be affected by contractions of muscles spanning the hip joint, no information is available to date. We examined how the stiffness (force attenuation capacity) and energy absorption of the trochanteric soft tissue were affected by hip muscle activation during a fall. Thirteen healthy young individuals (5 males, 8 females) participated in the pelvis release experiment. Falling trials were acquired with three muscle contraction conditions: 0–20% (“relaxed”), 20–50% (“moderate”), and 60–100% (“maximal”) of the maximal voluntary isometric contraction of the gluteus medius muscle. During trials, we measured real-time force and deformation behaviour of the trochanteric soft tissue. Outcome variables included the stiffness and energy absorption of the soft tissue. The stiffness and energy absorption ranged from 56.1 to 446.9 kN/m, and from 0.15 to 2.26 J, respectively. The stiffness value increased with muscle contraction, and 59% greater in “maximal” than “relaxed” condition (232.2 (SD = 121.4) versus 146.1 (SD = 49.9)). However, energy absorption decreased with muscle contraction, and 58.9% greater in “relaxed” than “maximal” condition (0.89 (SD = 0.63) versus 0.56 (SD = 0.41)). Our results provide insights on biomechanics of the trochanteric soft tissue (“natural” padding device) during impact stage of a fall, suggesting that soft tissues’ protective benefits are largely affected by the level of muscle contraction.

Biomechanics of the trochanteric soft tissue during a fall and hip fracture in older adults

Biomechanics of the trochanteric soft tissue during a fall and hip fracture in older adults

Fatty infiltration of hip muscles and trochanteric soft tissue thickness are associated with hip fractures in the elderly.

Apart from bone conditions, muscle and soft tissue parameters might also influence hip fractures. We aimed to evaluate the association between hip muscle and trochanteric soft tissue parameters and hip fractures. We retrospectively reviewed 60 patients with hip fractures and 114 controls without hip fractures.Cases and controls were matched for age, sex, and body mass index using propensity score matching. Muscle cross-sectional area (CSA), mean attenuation, and fatty infiltration rate (FIR) (proportion of intramuscular fat content) were measured on CT images for the gluteus maximus, the gluteus medius/minimus, and the anterior and medial compartments of the upper thigh. Trochanteric soft tissue thickness (TSTT) and femoral neck attenuation were also measured. Univariate and multivariate analyses were conducted to identify potential risk factors of hip fractures. Patients with hip fractures had significantly lower femoral neck attenuation, TSTT, and CSA of the gluteus maximus and anterior compartment than controls. FIR of all hip muscle groups were significantly higher in hip fracture patients than controls. Multivariate analysis revealed that every 1% increase in FIR of medial compartment independently increased the odds of hip fractures by 23.7% (OR = 1.237, 95% CI = 1.093-1.401) and every 1cm longer TSTT independently decreased the odds by 32.8% (OR = 0.672, 95% CI = 0.477-0.946). Fatty infiltration of hip muscles can better discriminate hip fractures than muscle area. Increased TSTT is independently associated with low fracture risk.

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

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

The Effects of Body Position on Trochanteric Soft Tissue Thickness-Implications for Predictions of Impact Force and Hip Fracture Risk During Lateral Falls.

Trochanteric soft tissue thickness (TSTT) is a protective factor against fall-related hip fractures. This study's objectives were to determine: (1)the influence of body posture on TSTT and (2)the downstream effects of TSTT on biomechanical model predictions of fall-related impact force (Ffemur) and hip fracture factor of risk. Ultrasound was used to measure TSTT in 45 community-dwelling older adults in standing, supine, and side-lying positions with hip rotation angles of -25°, 0°, and 25°. Supine TSTT (mean [SD] = 5.57 [2.8]cm) was 29% and 69% greater than in standing and side-lying positions, respectively. The Ffemur based on supine TSTT (3380 [2017]N) was 19% lower than the standing position (4173 [1764]N) and 31% lower than the side-lying position (4908 [1524]N). As factor of risk was directly influenced by Ffemur, the relative effects on fracture risk were similar. While less pronounced (<10%), the effects of hip rotation angle were consistent across TSTT, Ffemur, and factor of risk. Based on the sensitivity of impact models to TSTT, these results highlight the need for a standardized TSTT measurement approach. In addition, the consistent influence of hip rotation on TSTT (and downstream model predictions) support its importance as a factor that may influence fall-related hip fracture risk.

Anatomically Aligned Loading During Falls: Influence of Fall Protocol, Sex and Trochanteric Soft Tissue Thickness.

Fall simulations provide insight into skin-surface impact dynamics but have focused on vertical force magnitude. Loading direction and location (relative to the femur) likely influence stress generation. The current study characterized peak impact vector magnitude, orientation, and center of pressure over the femur during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulations including a vertical pelvis release, as well as kneeling and squat releases, which incorporate lateral/rotational motion. Force magnitude and direction varied substantially across fall simulations. Kneeling and squat releases elicited 57.4 and 38.8% greater force than pelvis release respectively, with differences accentuated in males. With respect to the femoral shaft, kneeling release had the most medially and squat release the most distally directed loading vectors. Across all fall simulations, sex and TSTT influenced force magnitude and center of pressure. Force was 28.0% lower in females and was applied more distally than in males. Low-TSTT participants had 16.8% lower force, applied closer to the greater trochanter than high-TSTT participants. Observed differences in skin-surface impact dynamics likely interact with underlying femur morphology to influence stress generation. These data should serve as inputs to tissue-level computational models assessing fracture risk.

Factors that influence the distribution of impact force relative to the proximal femur during lateral falls

In-vivo fall simulations generally evaluate hip fracture risk through differences in impact force magnitude; however, the distribution of force over the hip likely modulates loading and subsequent injury risk of the underlying femur. The current study characterized impact force distribution over the hip during falls, and the influence of biological sex and trochanteric soft tissue thickness (TSTT). Forty young adults completed fall simulation protocols (FSP) including highly controlled vertical pelvis and more dynamic kneeling and squat releases. At the instant of peak force, percentage of impact force applied in a circular region (r = 5 cm) centered over the greater trochanter (FGT%) was determined to characterize force localization. To assess the need for anatomically aligned pressure analysis, this process was repeated utilizing peak pressure location as a surrogate for the greater trochanter (FPP%). FGT% was 10.8 and 21.9% greater in pelvis release than kneeling and squat releases respectively. FGT% was 19.1 and 30.4% greater in males and low-TSTT individuals compared to females and high-TSTT individuals. TSTT explained the most variance (43.7–55.3%) in FGT% across all protocols, while sex explained additional variance (5.3–19.0%) during dynamic releases. In all FSP, TSTT-groups and sexes, average peak pressure location was posterior and distal to the GT. FPP% overestimated FGT% by an average of 15.7%, highlighting the need for anatomically aligned pressure analysis. This overestimation was FSP and sex dependent, minimized during pelvis release and in males. The data have important implications from clinical and methodological perspectives, and for implementation in tissue-level computational models.

Characterizing Viscoelastic Property of Soft Tissue Over the Hip as a Risk Factor of Pressure Ulcer

Background: A pressure ulcer is common in soft tissue over the greater trochanter (GT) in side-lying position, and sustained tissue deformation induced by the prolonged external force is a primary cause, which can be discussed with soft tissues’ viscoelastic properties (i.e., stress relaxation, creep response). Objects: Using an automated hand-held indentation device, we measured the viscoelastic properties of soft tissue over the hip area, in order to examine how the properties are affected by site with respect to the GT. Methods: Twenty participants (15 males and 5 females) who aged from 21 to 32 were participated. An automated hand-held indentation device was used to measure the stress relaxation time and creep response. Trials were acquired for three different locations with respect to the GT (i.e., right over the GT, 6 cm anterior or posterior to the GT). For each location, five trials were acquired and averaged for data analyses. Results: Soft tissues’ stress relaxation time and creep response were associated with site (F = 23.98, p < 0.005; F = 24.09, p < 0.005; respectively). The stress relaxation time was greatest at posterior gluteal region (19.22 ± 2.49 ms), and followed by anterior region (15.39 ± 2.47 ms) and right over the GT (14.40 ± 3.18 ms). Similarly, creep response was greatest at posterior gluteal region (1.16 ± 0.14), and followed by anterior region (0.95 ± 0.14) and right over the GT (0.89 ± 0.18). Conclusion: Our results showed that the stress relaxation and creep were greatest at the posterior gluteal region and least at right over the GT, indicating that the gluteal soft tissue is more protective to the prolonged external force, when compared to the trochanteric soft tissue. The results suggest that a risk of pressure ulcer over the GT may decrease with slightly posteriorly rotated side-lying position.

Effect of Impact Velocity, Flooring Material, and Trochanteric Soft-Tissue Quality on Acetabular Fracture during a Sideways Fall: A Parametric Finite Element Approach

A low-energy acetabular fracture, as a result of falling from standing height, is common among elderly patients and the number of cases is increasing rapidly in developed countries. Several biomechanical factors contribute to the incidence, severity, and type of acetabular fractures, such as body configuration at the impact moment or bone and soft-tissue quality. The current parametric study developed a comprehensive finite element model of the pelvic girdle and simple representation of the whole body and investigated the effects of impact velocity, conventional indoor/outdoor flooring material, and trochanteric soft-tissue stiffness on an acetabular fracture. Our results show that whereas the impact velocity has a substantial influence on the incidence and type of acetabular fracture, the effects of conventional flooring materials and trochanteric soft-tissue quality are not remarkable. It seems that other factors such as the quality of bone (healthy vs. osteoporotic), the thickness of trochanteric soft-tissue, and body configuration at the impact are more critical in the occurrence and type of the acetabular fracture. These results can be valuable in the prevention of acetabular fractures and the design of protective measures such as hip pads or novel flooring materials.

Assessment of the force attenuation capability of 3D printed hip protector in simulated sideways fall

An innovative 3D printed hip protector has been designed and tested to decrease the possibility of hip fracture in a sideways fall to a hard surface. The main design purpose was to create custom fit hip protector, reduce the manufacturing period and make the protector comfortable to wear. This work compares the new energy shunting 3D printed hip protector design with an existing energy absorbing hip protector. A drop tower mechanical test rig was designed and developed to simulate a sideways fall with sufficient impact energy to fracture an unprotected greater trochanter (GT). The test rig incorporates the actual geometry of a femur made from steel and uses a foam to simulate trochanteric soft tissue over the greater trochanter. Similar impact energy was used for the testing of each hip protector. The weight of the striker mass was maintained, and the height was adjusted to obtain an impact energy of 21–43J to produce femoral neck force of 3–9 kN. Results illustrate that the 3D hip protector compares favorably in attenuating impact force capable of causing hip fracture to a value below the fracture threshold of 3.472 kN. The influence of the 3D hip protector on peak transmitted forces to the vulnerable site of the greater trochanter is shown to be positive. It is anticipated that future protectors can be 3D printed after optimizations to end the bundling of same hip protector for different body geometry.

Study of sex differences in the association between hip fracture risk and body parameters by DXA-based biomechanical modeling

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.

Factors that influence soft tissue thickness over the greater trochanter: application to understanding hip fractures.

Fall-related hip injuries are a concern for the growing population of older adults. Evidence suggests that soft tissue overlying the greater trochanter attenuates the forces transmitted to the proximal femur during an impact, reducing mechanical risk of hip fracture. However, there is limited information about the factors that influence trochanteric soft tissue thickness. The current study used ultrasonography and electromyography to determine whether trochanteric soft tissue thickness could be quantified reproducibly and whether it was influenced by: (1) gender; (2) hip postures associated with potential falling configurations in the sagittal plane (from 30° of extension to 60° of flexion, at 15° intervals), combined adduction-flexion, and combined adduction-extension; and (3) activation levels of the tensor fascia lata (TFL) and gluteus medius (GM) muscles. Our results demonstrated that soft tissue thickness can be measured reliably in nine hip postures and three muscle activation conditions (for all conditions, ICC >0.98). Mean (SD) thickness in quiet stance was 2.52 cm. Thickness was 27.0% lower for males than females during quiet stance. It was 16.4% greater at maximum flexion than quiet standing, 27.2% greater at maximum extension, and 12.5% greater during combined adduction-flexion. However, there was no significant difference between combined adduction-extension and quiet standing. Thickness was not affected by changes in muscle activity. Forces applied to the femoral neck during a lateral fall decrease as trochanteric soft tissue thickness increases; gender and postural configuration at impact could influence the loads applied to the proximal femur (and thus hip fracture risk) during falls on the hip.

Development of an Inertia-Driven Model of Sideways Fall for Detailed Study of Femur Fracture Mechanics

A new method for laboratory testing of human proximal femora in conditions simulating a sideways fall was developed. Additionally, in order to analyze the strain state in future cadaveric tests, digital image correlation (DIC) was validated as a tool for strain field measurement on the bone of the femoral neck. A fall simulator which included models for the body mass, combined lateral femur and pelvis mass, pelvis stiffness, and trochanteric soft tissue was designed. The characteristics of each element were derived and developed based on human data from the literature. The simulator was verified by loading a state-of-the-art surrogate femur and comparing the resulting force-time trace to published, human volunteer experiments. To validate the DIC, 20 human proximal femora were prepared with a strain rosette and speckle paint pattern, and loaded to 50% of their predicted failure load at a low compression rate. Strain rosettes were taken as the gold standard, and minimum principal strains from the DIC and the rosettes were compared using descriptive statistics. The initial slope of the force-time curve obtained in the fall simulator matched published human volunteer data, with local peaks superimposed in the model due to internal vibrations of the spring used to model the pelvis stiffness. Global force magnitude and temporal characteristics were within 2% of published volunteer experiments. The DIC minimum principal strains were found to be accurate to 127±239 μɛ. These tools will allow more biofidelic laboratory simulation of falls to the side, and more detailed analysis of proximal femur failure mechanisms using human cadaver specimens.

Hip fracture and anthropometric variations: Dominance among trochanteric soft tissue thickness, body height and body weight during sideways fall

BackgroundHip fracture depends on various anthropometric parameters such as trochanteric soft tissue thickness, body height and body weight. The objective was to evaluate the responses to the variations in anthropometric parameters during sideways fall, and to identify the most dominant parameter among them. MethodSeven finite element models were developed having anthropometric variations in trochanteric soft tissue thickness (5–26mm), body height (1.70–1.88m), and body weight (63–93.37kg). These were simulated for sideways fall with ANSYS-LS-DYNA® code. FindingsSignificant effect of trochanteric soft tissue thickness variation was found on ‘normalized peak impact force with respect to the body weight’ (p=0.004, r2=0.808) and strain ratio (p=0.083, r2=0.829). But, variation in body height was found to be less significant on normalized peak impact force (p=0.478, r2=0.105) and strain ratio (p=0.292, r2=0.217). Same was true for the variation in body weight on normalized peak impact force (p=0.075, r2=0.456) and strain ratio (p=0.857, r2=0.007). The risk factor for fracture was also well correlated to the strain ratio for the inter-trochanteric zone (p<0.0007, r2=0.917) where the most fractures are clinically observed to happen. InterpretationsTrochanteric soft tissue thickness was found likely to be the most dominant parameter over body height and body weight, signifying that a slimmer elderly person, taller or shorter, with less trochanteric soft tissue thickness should be advised to take preventive measures against hip fracture under sideways fall.

Estimation of Trochanteric Soft Tissue Thickness From Dual-Energy X-ray Absorptiometry

Low body mass index is considered to be an important risk factor for fractures in postmenopausal women, in part reflecting its association with lower bone mineral density (BMD). In contrast, obesity is thought to be protective against fracture because of higher BMD and reduced transmitted force of falls as a result of soft tissue padding. Dual-energy X-ray absorptiometry (DXA) is most widely used for the assessment of osteoporosis. We hypothesized that trochanteric soft tissue thickness, as measured directly on whole-body DXA scans, could be estimated using the regional measures of anteroposterior tissue thickness from hip and spine DXA. We identified 376 adult patients who underwent DXA evaluation of the lumbar spine, hip, and whole body at the same visit. The population was randomly divided into 2 equal-sized subgroups, one used to derive prediction equations for trochanteric soft tissue thickness and the other for independent validation. Compared with the actual measurement from the whole-body scans in the validation cohort, the DXA-based estimate gave an unbiased prediction of trochanteric soft tissue thickness (adjusted R² was 0.60 with a standard error of the estimate of 1.35cm), which was significantly better than estimation obtained without DXA information (p < 0.001). Area under the curve discrimination for trochanteric soft tissue thickness in the lowest and highest tertiles was 0.901 (95% confidence interval: 0.849–0.953) and 0.859 (95% confidence interval: 0.805–0.915), respectively. Model-based prediction of trochanteric soft tissue thickness in the lowest and highest tertiles had sensitivities of 78.5% and 91.9% and specificities of 64.4% and 86.8%, respectively. We conclude that regional DXA scans of the spine and hip can be used to estimate the trochanteric soft tissue thickness.

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

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). 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. 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. 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). 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.

Comparison of hip fracture risk prediction by femoral aBMD to experimentally measured factor of risk

Areal BMD (aBMD) derived from DXA is currently the gold standard for diagnosis of osteoporosis. A biomechanical approach to fracture risk assessment comparing the ratio of applied load to bone strength, termed the factor of risk (Φ), may be useful to better identify patients at risk for fracture. We obtained 73 human cadaveric femurs (48 women and 25 men, aged 74.2±8.7 years, range 55–98 years), measured femoral neck (FN) aBMD by DXA, and mechanically tested the femurs to failure in a sideways fall configuration. The force applied to the hip during a sideways fall was estimated from height and weight, and accounted for trochanteric soft tissue thickness. Compared to men, women had significantly lower FN aBMD and femoral strength, and tended to have higher factor of risk for hip fracture Φ. Fifty-three of 54 (98%) specimens that had a FN aBMD T-score below −2.5 also had a Φ>1. However, 10/19 (53%) specimens with FN aBMD T-score above −2.5 also had Φ>1. These data indicate that whereas an aBMD-based diagnosis of osteoporosis is highly associated with fracture risk as assessed by the factor of risk, about 50% of individuals not designated as osteoporotic by aBMD testing would be at high risk for hip fracture should they experience a sideways fall. These findings strongly support the investigation of new biomechanically-based methods of fracture risk prediction.

Effects of trochanteric soft tissue thickness and hip impact velocity on hip fracture in sideways fall through 3D finite element simulations

A major worldwide health problem is hip fracture due to sideways fall among the elderly population. The effects of sideways fall on the hip are required to be investigated thoroughly. The objectives of this study are to evaluate the responses to trochanteric soft tissue thickness ( T) variations and hip impact velocity ( V) variations during sideways fall based on a previously developed CT scan derived 3D non-linear and non-homogeneous finite element model of pelvis–femur–soft tissue complex with simplified biomechanical representation of the whole body. This study is also aimed at quantifying the effects [peak impact force ( F max), time to F max, acceleration and peak principal compressive strain ( ε max)] of these variations ( T, V) on hip fracture. It was found that under constant impact energy, for 81% decrease in T (26–5 mm), F max and ε max increased by 38% and 97%, respectively. Hence, decrease in T (as in slimmer persons) strongly correlated to risk for hip fracture ( φ) and strain ratio (SR) by 0.972 and 0.988, respectively. Also under same T and body weight, for 75% decrease in V (4.79–1.2 m/s), F max and ε max decreased by 70% and 86%, respectively. Hence, increase in V (as in taller persons) strongly correlated to φ and SR by 0.995 and 0.984, respectively. For both variations in T and V, inter-trochanteric fracture situations were well demonstrated by φ as well as by SR and strain contours, similar to clinically observed fractures. These quantifications would be helpful for effective design of person-specific hip protective devices.