Proximal Femur Strength Research Articles

The Effect of Simulated Metastatic Lytic Lesions on Proximal Femoral Strength

Metastatic lesions in the proximal femur can reduce hip strength and lead to pathologic fracture. However, current methods for identifying patients at risk of pathologic fracture are inadequate. We hypothesized the percentage of intact proximal femoral strength remaining after formation of a simulated lytic defect within the femoral neck or at the level of the lesser trochanter depends on defect location within the respective region. Computed tomography scan-based finite element models of 12 cadaveric proximal femora were used to evaluate the effect of 20-mm-diameter spherical voids at various locations in the neck and at the level of the lesser trochanter. In both regions, the percentage of intact strength remaining depended on defect location (p < 0.001). In the neck, the strength of specimens with inferomedial defects (median, 50.4% of intact; range, 27.8-71.7%) was less than the strength of specimens with defects located in the center of the neck, superolaterally, or anteriorly (p < 0.05). Near the lesser trochanter, anteromedial defects resulted in the lowest strength (median, 66.6% of intact; range, 49.2-73.8%). Other defects at the level of the lesser trochanter had a markedly smaller effect. These findings may be helpful for evaluating pathologic fracture risk.

Densitometric, morphometric and mechanical distributions in the human proximal femur

With the prevalent use of DXA-measured BMD to assess pathologic hip fractures and its recently reported lack of reliability to predict fracture or account for efficacy of anti-resorptive therapy, it is reasonable to assess whether variations in the primary and secondary tensile and compressive trabecular microstructure can account for variations in proximal femur strength in comparison to DXA-measured BMD. To that end, microstructural and densitometric measures of trabecular bone specimens, from discrete sites within the proximal femur, were correlated with their mechanical properties. We hypothesize that accounting for regional variations in trabecular microstructure will improve predictions of proximal femur strength and stiffness compared to bone density measured by DXA. Forty-seven samples (seven donors) from seven distinct sites of human proximal femur underwent DXA and μCT imaging and mechanical testing. The results revealed significant variations in BMC, morphometric indices and mechanical properties within the proximal femur. This work has demonstrated that the mechanical performance of each sub-region is highly dependent on the corresponding trabecular microstructure. BMD measured by DXA at standard regions of interest cannot resolve the variations in trabecular density and microstructure that govern the mechanical behavior of the proximal femur. This work suggests that a quantitative Singh index that uses high resolution QCT to monitor the trabecular microstructure at specific sub-regions of the proximal femur may allow better predictions of hip fracture risk in individual patients and an improved assessment of changing bone structure in response to pharmacological interventions.

Prediction of bone strength using a CT based finite element method

Hip fractures are the most serious complication of osteoporosis and have been recognized as a major public health problem. In elderly persons, hip fractures occur as a result of increased fragility of the proximal femur due to osteoporosis. It is essential to precisely quantify the strength of the proximal femur in order to estimate the fracture risk and plan preventive interventions. Computed tomography (CT)-based finite element analysis could possibly achieve precise assessment of the strength of the proximal femur. We have developed a three dimensional simulation model that could accurately predict the strength and surface strains of the proximal femur using a CT-based finite element method. The axial CT scans of the proximal femora were obtained with a calibration phantom, from which the 3D finite element models were constructed. Materially nonlinear finite element analyses were performed. The yield and fracture loads were calculated, while the sites where elements failed and the distributions of the principal strains and stresses were determined. The simulation is patient specific and could provide us of a useful tool to evaluate fracture risk in patients with osteoporosis. The technology utilized in this method would make a rapid progress in accordance with the progress of both imaging and computer technologies and much more precise prediction of the fracture risk will be realized in the near future.

Femoral neck cortical geometry measured with magnetic resonance imaging is associated with proximal femur strength

Magnetic resonance imaging (MRI) is a promising medical imaging technique that we used to assess femoral neck cortical geometry. Our primary objective was to assess whether cortical bone in the femoral neck assessed by MRI was associated with failure load in a simulated sideways fall, with and without adjustment for total bone size. Our secondary objective was to assess the reliability of the MRI measurements. We imaged 34 human cadaveric proximal femora using MRI and dual-energy X-ray absorptiometry (DXA). MRI measurements of cross-sectional geometry at the femoral neck were the cortical cross-sectional area (CoCSA(MRI)), second area moment of inertia (x axis; Ix(MRI)), and section modulus (x axis; Zx(MRI)). DXA images were analyzed with the standard Hologic protocol. From DXA, we report the areal bone mineral density (aBMD(DXA)) in the femoral neck and trochanteric subregions of interest. The femora were loaded to failure at 100 mm/s in a sideways fall configuration (15 degrees internal rotation, 10 degrees adduction). Failure load (N) was the primary outcome. We observed that the femoral neck CoCSA(MRI) and Ix(MRI) were strongly associated with failure load (r (2)=0.46 and 0.48, respectively). These associations were similar to those between femoral neck aBMD and failure load (r (2)=0.40), but lower than the associations between trochanteric aBMD and failure load (r (2)=0.70). We report that MRI holds considerable promise for measuring cortical bone geometry in the femoral neck and for predicting strength at the proximal femur.

Predicting Proximal Femoral Strength Using Structural Engineering Models

Hip fracture related to osteoporosis and metastatic disease is a major cause of morbidity and mortality. An accurate and precise method of predicting proximal femoral strength and fracture location would be useful for research and clinical studies of hip fracture. The goals of this study were to develop a structural modeling technique that accurately predicts proximal femoral strength; to evaluate the accuracy and precision of this predicted strength on an independent data set; and to evaluate the ability of this technique to predict fracture location. Fresh human cadaveric proximal femora with and without metastatic lesions were studied using computed tomography scan-based three-dimensional structural models and mechanical testing to failure under single-limb stance-type loading. The models understated proximal femoral strength by an average of 444 N, and the precision of the predicted strength was +/- 1900 N. Therefore, the ability to predict hip strength in an individual subject is limited primarily by the level of precision, rather than accuracy. This level of precision is likely to be sufficient for many studies of hip strength. Finally, these models predict fractures involving the subcapital and cervical regions, consistent with most fractures produced experimentally under single-limb stance-type loading.

Improved prediction of proximal femoral fracture load using nonlinear finite element models

Hip fracture, which is often due to osteoporosis or other conditions affecting bone strength, can lead to permanent disability, pneumonia, pulmonary embolism, and/or death. Great effort has been directed toward developing noninvasive methods for evaluating proximal femoral strength (fracture load), with the goal of assessing fracture risk. Previously, computed tomographic scan-based, linear finite element (FE) models were used to estimate proximal femoral fracture loads ex vivo in two load configurations, one approximating joint loading during single-limb stance and the other simulating impact from a fall. Measured and computed fracture loads were correlated (stance, r=0.867; fall, r=0.949). However, precision for the stance configuration was insufficient to identify subjects with below average fracture loads reliably. The present study examined whether, for this configuration, nonlinear FE models could be used to identify these subjects. These models were found to predict fracture load within ±2.0 kN ( r=0.962). This level of precision is sufficient to identify 97.5% of femora with fracture loads 1.3 standard deviations below the mean as having below average fracture loads. Accordingly, 20% of subjects with below average fracture loads, i.e. those with the lowest fracture loads and likely to be at greatest risk of fracture, would be correctly identified with at least 97.5% reliability. This FE modeling method will be a powerful tool for studies of hip fracture.

Weight bearing exercise and increased dietary calcium intake have a synergistic effect on bone mass accrual at the femur in pre- and early pubescent girls

There is evidence that quantitative ultrasound (QUS) at the proximal femur involves waves propagating circumferentially in the cortical shell. These waves, in theory, convey information on bone geometrical and material characteristics and thus have the potential to improve fracture risk prediction. In this work, the time-of-flight (TOF) of the first arriving signal (FAS) that corresponds to waves propagating circumferentially is considered. The relationships between the TOF of the FAS and geometrical features of the femoral neck are investigated. Five neck cross-sections from 11 human femurs from females (>65y) were extracted from 3-D X-ray quantitative computed tomography (XR-QCT) datasets. Geometrical parameters including cross-sectional area (CSA), minimum moment of inertia (Imin) and section modulus (Z) were computed from femoral neck cross-section images. Two-dimensional numerical simulation of US propagation through femoral neck was performed and TOF of the FAS was estimated. TOF was best correlated with Imin: R2=0.82 (p=10−4; RMSE=1390mm4 [13%]) in the region between proximal and mid-femoral neck and with Z: R2=0.55 (p<10−2; RMSE=480mm3 [17%]) and CSA: R2=0.62 (p<5.10−3; RMSE=22mm2 [7%]) in the mid-femoral neck. The results suggest that QUS has the potential to assess proximal femur strength based on estimates of geometrical properties of the cortical shell. (E-mail: [email protected])

Relationships between femoral fracture loads for two load configurations

Studies of proximal femoral strength usually involve one of two types of loading conditions, loading similar to joint loading during single-limb stance or loading simulating impact from a fall. When interpreting the results of studies involving only one of these load configurations, the question arises as to their applicability to the other configuration. In addition, it is desirable to know whether, for an individual bone, fracture load for one load configuration is indicative of fracture load for the other configuration. In this study, the relationship between proximal femoral fracture loads for single-limb stance loading and loading simulating impact from a type of fall was determined from mechanical testing of 17 matched pairs of human proximal femora. Fracture loads for these two configurations were found to be linearly related ( r=0.901, p<0.001). However, the correlation between fracture loads is not notably stronger than correlations currently available between fracture load and measures of bone density and geometry. In addition, the regression results indicate that 81% of the variance in fracture load for one loading condition is accounted for by fracture load for the other loading condition. Thus, 19% of the variance remains unexplained, indicating that the results of studies involving only one load configuration are not necessarily indicative of those that would be found for another configuration.

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

Quantitative ultrasound (QUS) of the heel and tibia have recently been approved in the United States for diagnostic evaluation of low bone mass. The goal of this study was to use human cadaveric specimens to compare correlations among: a) strength of the proximal femur; b) bone mineral density of the femur, tibia, and heel; and c) QUS of the tibia and heel. We obtained 26 proximal femurs and intact lower limbs from 16 female and 10 male cadavers, with a mean age of 81 ± 12 years. Bone mineral density (BMD, g/cm 2) of the proximal femur and tibia were assessed using dual-energy x-ray absorptiometry, and BMD (g/cm) of the heel was measured using single-energy x-ray absorptiometry. Ultrasound velocity at the mid-tibia was determined using a contact, gel-coupled ultrasound device. Broadband ultrasound attenuation (BUA) and speed of sound (SOS) of the heel were determined using a transmission ultrasound device with water-based coupling. The femurs were tested to failure in a configuration designed to simulate a fall to the side with impact to the greater trochanter. As in previous studies, the strength of the proximal femur was very strongly correlated with femoral BMD and heel BMD (r 2 = 0.78–0.92, p < 0.0001 for all). BUA and SOS of the heel were also strongly correlated to femoral strength (r 2 = 0.70 and 0.67, respectively, p < 0.0001 for both), whereas tibia SOS was only weakly correlated (r 2 = 0.19, p = 0.03). The average coefficient of variation for triplicate tibial SOS measurements was 0.50%. This study indicates that, although tibial SOS measurements are precise, they are not strongly correlated with femoral BMD or strength. In contrast, heel QUS measurements are strongly correlated with the strength of the proximal femur. These findings imply that tibial SOS may be of limited use for assessing hip fracture risk. Prospective fracture risk data are needed to define further the clinical utility of tibia ultrasound measurements.

Decrease in canine proximal femoral ultimate strength and stiffness due to fatigue damage

Fractures of the proximal femur represent a significant health concern especially in the elderly, Fatigue damage and microfractures have been implicated in the etiology of hip fractures; however, the extent to which these factors are sufficient to bring about significant reductions in proximal femur strength and stiffness is unknown. This study examined the hypothesis that fatigue loading of the proximal femur results in highly correlated decreases in bone stiffness and strength through the accumulation of bone microdamage. One canine femur from each of 10 pairs was monotonically loaded to failure to determine the ultimate strength. The contralateral femur was then cyclically loaded at 50% of the ultimate load value for either 3600 cycles or until a 40% reduction in stiffness was achieved. This femur was then monotonically loaded to failure. For two additional femur pairs, the fatigued femur was histologically processed to reveal bone microdamage. In support of the hypothesis, the data demonstrated a linear relationship between strength loss and stiffness loss (Adj. R 2 = 0.79, p < 0.0004) with significant decreases in residual whole bone strength ( p < 0.004) following cyclic loading. In addition, damage (microcracks) in the cortical bone and broken trabeculae were observed in the neck and head region of the femur fatigued until its stiffness was reduced by 40% but not fractured subsequent to cyclic loading.

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

Femoral neck axis length, neck width, and neck-shaft angle were measured on radiographs of right proximal femora from 64 cadavers (28 female, 36 male). Bone mineral density (BMD) was measured using dual energy X-ray absorptiometry (DXA) for various regions of interest, and quantitative computed tomography (QCT) was used to determine BMD and bone areas for cortical and trabecular bone at the trochanter and femoral neck. The strength of the femur was determined by a mechanical test simulating a fall on the greater trochanter, and the fracture type (cervical or trochanteric) was subsequently determined from radiographs. Twenty-six cervical fractures and 38 trochanteric fractures were observed, with no significant sex difference in the distribution of fracture types. Femoral strength was significantly elevated in males compared to females. DXA trochanteric BMD was more strongly ( p < 0.05) correlated with femoral strength ( r 2 = 0.88) than were any of the other DXA BMD measurements ( r 2 = 0.59–0.76). In multiple regression models, a combination of different DXA BMD measurements produced only a small increase (1%) in the explained variability of femoral strength. Of the OCT measurements, trochanteric cortical area yielded the optimal correlation with femoral strength ( r 2 = 0.83). Weak, but significant, correlations were observed between femoral strength and cortical BMD at trochanteric ( r 2 = 0.28) and neck regions ( r 2 = 0.07). In multiple regression models, combining QCT parameters yielded, at best, an r 2 of 0.87. Of the geometrical parameters, both neck axis length and neck width were significantly correlated with femoral strength ( r 2 = 0.24, 0.22, respectively), but no significant correlation was found between strength and the neckshaft angle. Combining DXA trochanteric BMD with femoral neck width resulted in only a small increase in the explained variability (1%) compared to trochanteric BMD alone. The results demonstrated that DXA and QCT had a similar ability to predict femoral strength in vitro. Trochanteric BMD was the best DXA parameter, and cortical area (not cortical BMD) was the optimal QCT parameter. Geometric measurements of the proximal femur were only weakly correlated with the mechanical strength, and combinations of DXA, QCT, and geometric parameters resulted in only small increases in predictive power compared to the use of a single explanatory variable alone.

Proximal femoral strength predicted by DXA and QCT

Proximal femoral strength predicted by DXA and QCT

Trochanteric bone mineral density is associated with type of hip fracture in the elderly

Hip fractures can be separated into femoral neck (cervical or intracapsular) or trochanteric (extracapsular). Trochanteric fractures have been associated with up to twice the short-term mortality of cervical fractures in the elderly. Fracture type may be influenced by the fall direction and local differences in proximal femur strength properties. We previously demonstrated that fall characteristics and body habitus, in addition to femoral bone mineral density, play a dominant role in the prediction of hip fracture in elderly fallers. To examine the association of these determinants with hip fracture type, we assessed fall characteristics, body habitus, and site-specific bone mineral density measurements in 112 elderly hip fracture patients (85 women and 27 men, mean age 85 years) 1 week after an acute hip fracture. Trochanteric BMD was 13% lower in women and 11% lower in men for patients with trochanteric fracture than in those with femoral neck fracture (p < 0.01). A stepwise multiple logistic regression indicated that trochanteric BMD (decrease of 1.0 SD, adjusted OR 4.6, 95% Cl 2.0-9.5, p < 0.0001) and femoral neck BMD (increase of 1.0 SD, adjusted OR 3.0, 95% Cl 1.6-5.9, p = 0.0003) were independently associated with trochanteric fracture. Fall characteristics, body habitus, gender, and age were not associated with hip fracture type. We conclude that a relatively low trochanteric BMD or a high femoral neck BMD was associated with a trochanteric hip fracture and that site-specific trochanteric BMD determinations should be measured when assessing risk of trochanteric hip fractures in the elderly.

The Role of Osteoporosis in Intertrochanteric Fractures

Osteoporosis is not the only factor that determines success in treating intertrochanteric fractures. Singh's index provides a simple and useful method for measuring this factor, however, and it should not be ignored. The index helps to predict the fractures that involve increased risk of fixation failure. It can serve as one of the guides for deciding about appropriate treatment. And if we fail to include some estimate of proximal femur strength in our evaluations of fracture results, we cannot learn how to improve those results.