Mechanical strength of the proximal femur as predicted from geometric and densitometric bone properties at the lower limb versus the distal radius

Impact forces in backward falls: Subject-specific video-based rigid body simulation of backward falls

A critical missing component in the study of real-world falls is the ability to accurately determine impact forces resulting from the fall. Subject-specific rigid body dynamic (RBD) models calibrated to video captured falls can quantify impact forces and provide additional insights into injury risk factors. RBD models were developed based on five backward falls captured on surveillance video in long-term care facilities in British Columbia, Canada. Model joint stiffness and initial velocities were calibrated to match the kinematics of the fall and contact forces were calculated. The effect of joint stiffnesses (neck, lumbar spine, hip, and knee joint) on head contact forces were determined by modifying the calibrated stiffness values ±25%. Fall duration, fall trajectories, and maximum velocities showed a close match between fall events and simulations. The maximum value of pelvic velocity difference between Kinovea (an open-source software 2D digitization software) and Madymo multibody modeling was found to be 6% ± 21.58%. Our results demonstrate that neck and hip stiffness values have a non-significant yet large effect on head contact force (t(3) = 1, p = 0.387 and t(3) = 2, p = 0.138), while lower effects were observed for knee stiffness, and the effect of lumbar spine stiffness was negligible. The subject-specific fall simulations constructed from real world video captured falls allow for direct quantification of force outcomes of falls and may have applications in improving the assessment of fall-induced injury risks and injury prevention methods.

The Influence of Fall Direction and Hip Protector on Fracture Risk: FE Model Predictions Driven by Experimental Data

Hip fractures in older adults, which often lead to lasting impairments and an increased risk of mortality, are a major public health concern. Hip fracture risk is multi-factorial, affected by the risk of falling, the load acting on the femur, and the load the femur can withstand. This study investigates the influence of impact direction on hip fracture risk and hip protector efficacy. We simulated falls for 4 subjects, in 7 different impact directions (15° and 30° anterior, lateral, and 15°, 30°, 60°, and 90° posterior) at two different impact velocities (2.1 and 3.1 m/s), all with and without hip protector, using previously validated biofidelic finite element models. We found the highest number of fractures and highest fragility ratios in lateral and 15° posterior impacts. The hip protector attenuated femur forces by 23-49 % for slim subjects under impact directions that resulted in fractures (30° anterior to 30° posterior). The hip protector prevented all fractures (6/6) for 2.1 m/s impacts, but only 10% of fractures for 3.1 m/s impacts. Our results provide evidence that, regarding hip fracture risk, posterior-lateral impacts are as dangerous as lateral impacts, and they support the efficacy of soft-shell hip protectors for anterior- and posterior-lateral impacts.

Bringing Mechanical Context to Image-Based Measurements of Bone Integrity

PURPOSE OF REVIEW

Image-based measurements of bone integrity are used to estimate failure properties and clinical fracture risk. This paper (1) reviews recent imaging studies that have enhanced our understanding of the mechanical pathways to bone fracture and (2) discusses the influence that inter-individual differences in image-based measurements may have on the clinical assessment of fracture risk RECENT FINDINGS: Increased tissue mineralization is associated with improved bone strength but reduced fracture toughness. Trabecular architecture that is important for fatigue resistance is less important for bone strength. The influence of porosity on bone failure properties is heavily dependent on pore location and size. The interaction of various characteristics, such as bone area and mineral content, can further complicate their influence on bone failure properties. What is beneficial for bone strength is not always beneficial for bone toughness or fatigue resistance. Additionally, given the large amount of imaging data that is clinically available, there is a need to develop effective translational strategies to better interpret non-invasive measurements of bone integrity.

Total urinary polyphenols and longitudinal changes of bone properties. The InCHIANTI study

The aim of this study was to evaluate the association of levels of urinary total polyphenols considered as a proxy measure of polyphenol intake, with longitudinal changes of bone properties, in the InCHIANTI study. Dietary intake of polyphenols appears to be associated with future accelerated deterioration of bone health.

INTRODUCTION

Polyphenols, micronutrients ingested through plant-based foods, have antioxidant and anti-inflammatory properties and may contribute to osteoporosis prevention. We evaluated associations of high levels of urinary total polyphenols (UTP), a proxy measure of polyphenol intake, with longitudinal changes of bone properties in a representative cohort of free-living participants of the InCHIANTI study.

METHODS

The InCHIANTI study enrolled representative samples from the registry list of two towns in Tuscany, Italy. Baseline data were collected in 1998 and follow-up visits in 2001 and 2004. Of the 1453 participants enrolled, 956 consented to donate a 24-h urine sample used to assess UTP, had dietary assessment, a physical examination, and underwent a quantitative computerized tomography (pQCT) of the tibia. From pQCT images, we estimated markers of bone mass (BM), diaphyseal design (DD), and material quality (MQ). Mixed models were used to study the relationship between baseline tertiles of UTP with changes of the bone characteristics over the follow-up.

RESULTS

At baseline, higher levels of UTP were positively correlated with markers of BM, DD, and MQ. Compared with lower tertile of UTP, participants in the intermediate and highest tertiles had higher cortical bone area, cortical mineral content, and cortical thickness. However, participants in the intermediate and highest UTP tertiles experienced accelerated deterioration of these same parameters over the follow-up compared with those in the lowest UTP tertile.

CONCLUSIONS

Dietary intake of polyphenols estimated by UTP and dietary questionnaire was associated with long-term accelerated deterioration of bone health. Our study does not support the recommendation of increasing polyphenol intake for osteoporosis prevention.

The effect of the hip impact configuration on the energy absorption provided by the femoral soft tissue during sideways falls

The femoral soft tissue (i.e., skin, muscle, fat) may play a key role in preventing hip fractures during a fall by absorbing the impact energy. We measured the femoral soft tissue deformation and associated compressive force during simulated sideways falls to estimate the energy absorbed by the soft tissue, and then examined how this was affected by the hip impact configuration and gender. Eighteen young adults (9 males and 9 females) participated in the pelvis release experiment. The pelvis was raised through a rope attached to an electromagnet on the ceiling, so the skin surface barely touches the ultrasound probe, which flush to a Plexiglas plate placed on a force plate. The electromagnet was turned off to cause a fall while the soft tissue deformation and associated compressive force were being recorded. Trials were acquired with three hip impact configurations. An outcome variable included the energy absorbed by the femoral soft tissue during a fall. The energy absorbed by the femoral soft tissue ranged from 0.03 to 3.05 J. Furthermore, the energy absorption was associated with the hip impact configuration (F = 4.69, p = 0.016). On average, the absorbed energy was 62% greater in posteriolateral than anteriolateral impact (0.92 versus 0.57 J). However, the energy absorption did not differ between male and female (F = 0.91, p = 0.36). The force-deflection behavior of the femoral soft tissue during a fall has been recorded, providing insights on the potential protective benefits of the soft tissue covering during a fall.

Numerical analysis of hip fracture due to a sideways fall

The primary purpose of this paper is to outline a methodology for evaluating the likelihood of cortical bone fracture in the proximal femur in the event of a sideways fall. The approach includes conducting finite element (FE) analysis in which the cortical bone is treated as an anisotropic material, and the admissibility of the stress field is validated both in tension and compression regime. In assessing the onset of fracture, two methodologies are used, namely the Critical Plane approach and the Microstructure Tensor approach. The former is employed in the tension regime, while the latter governs the conditions at failure in compression. The propagation of localized damage is modeled using a constitutive law with embedded discontinuity (CLED). In this approach, the localized deformation is described by a homogenization procedure in which the average properties of cortical tissue intercepted by a macrocrack are established. The key material properties governing the conditions at failure are specified from a series of independent material tests conducted on cortical bone samples tested at different orientations relative to the loading direction. The numerical analysis deals with simulations of experiments involving the sideways fall, and the results are compared with the experimental data. This includes both the evolution of fracture pattern and the local load-displacement characteristics. The proposed approach is numerically efficient, and the results do not display a pathological mesh-dependency. Also, in contrast to the XFEM approach, the analysis does not require any extra degrees of freedom.

Biomechanical in vitro examination of a standardized low-volume tubular femoroplasty

BACKGROUND

Osteoporosis is associated with the risk of fractures near the hip. Age and comorbidities increase the perioperative risk. Due to the ageing population, fracture of the proximal femur also proves to be a socio-economic problem. Preventive surgical measures have hardly been used so far.

METHODS

10 pairs of human femora from fresh cadavers were divided into control and low-volume femoroplasty groups and subjected to a Hayes fall-loading fracture test. The results of the respective localization and classification of the fracture site, the Singh index determined by computed tomography (CT) examination and the parameters in terms of fracture force, work to fracture and stiffness were evaluated statistically and with the finite element method. In addition, a finite element parametric study with different position angles and variants of the tubular geometry of the femoroplasty was performed.

FINDINGS

Compared to the control group, the work to fracture could be increased by 33.2%. The fracture force increased by 19.9%. The used technique and instrumentation proved to be standardized and reproducible with an average poly(methyl methacrylate) volume of 10.5 ml. The parametric study showed the best results for the selected angle and geometry.

INTERPRETATION

The cadaver studies demonstrated the biomechanical efficacy of the low-volume tubular femoroplasty. The numerical calculations confirmed the optimal choice of positioning as well as the inner and outer diameter of the tube in this setting. The standardized minimally invasive technique with the instruments developed for it could be used in further comparative studies to confirm the measured biomechanical results.

Effect of fall characteristics on the severity of hip impact during a fall on the ground from standing height

The magnitude of hip impact force during a fall on the ground (i.e., concrete surface) from standing height was determined. We found that this force decreases up to 59%, depending on how they land on the ground.

INTRODUCTION

We determined the magnitude of hip impact force that humans may experience in the event of a fall from standing height on the ground, in order to examine how the hip impact force was affected by characteristics of a fall.

METHODS

Twenty subjects mimicked a typical older adults' falls on a mat. Trials were acquired with three initial fall directions: forward, sideways, and backward. Trials were also acquired with three knee positions at the time of hip impact: knee together, knee on the mat, and free knee. During falls, attenuated vertical hip impact forces and corresponding depression of the mat were measured via a force plate placed under the mat and motion capture system, respectively. Using a mass-spring model, actual hip impact force and body stiffness during a fall on the ground were estimated.

RESULTS

Hip impact force averaged 4.0 kN (SD = 1.7). The hip impact force was associated with knee condition (F = 25.6, p < 0.005), but not with fall direction (F = 0.4, p = 0.599). Compared with "knee on the mat," hip impact force averaged 59% and 45% greater in "free knee" and "knee together," respectively (4.6 versus 2.9 kN, p < 0.005; 4.3 versus 2.9 kN, p < 0.005). However, the hip impact force did not differ between "free knee" and "knee together (4.6 versus 4.3 kN, p = 0.554).

CONCLUSION

Our results suggest that hip fracture risk during a fall decreases substantially, depending on how they land on the ground, informing the development of safe landing strategies to prevent fall-related hip fractures in older adults.

Hip fracture risk functions for elderly men and women in sideways falls

Falls among the elderly cause a huge number of hip fractures world-wide. The objective is to generate hip fracture force risk functions for elderly women and men in sideways falls which can be used for determining effectiveness of fall prevention measures as well as for individual assessment of fracture risk at the clinics. A literature survey was performed and ten publications were identified who contained several hundred individual femoral neck fracture forces in sideways fall for both elderly women and men. Theoretical distributions were tested for goodness of fit against the pooled dataset with the Anderson-Darling test (AD-test) and root mean square errors (RMSE) were extracted. According to the AD-test, a Weibull distribution is a plausible model for the distribution of hip fracture forces. A simple, exponential two-parameter Weibull function was therefore proposed, having a RMSE below 2.2% compared to the experimental distribution for both men and women. It was demonstrated that elderly women only can endure nearly half the proximal femur force for 5 and 10% fracture risk as elderly men. It should be noted though, that women were found to have significantly lesser body height and body weight which would produce less impact force during falls from standing height. The proposed sex-specific hip fracture risk functions can be used for biomechanically optimizing hip protectors and safety floors and for determining their effectiveness as a fall prevention measure.

Modification of honeycomb bioceramic scaffolds for bone regeneration under the condition of excessive bone resorption

Gallium (Ga) ions have been clinically approved for treating the diseases caused by the excessive bone resorption through the systemic administration. Nevertheless, little attention has been given to the Ga-containing biomaterials for repairing bone defects under the pathological condition of excessive bone resorption. In the current study, for the first time the Ga-containing phosphate glasses (GPGs) were introduced to modify the honeycomb β-tricalcium phosphate (β-TCP) bioceramic scaffolds, which were prepared by an extrusion method. The results indicated that the scaffolds were characterized by uniform pore structure and channel-like macropores. The addition of GPGs promoted densification of strut of scaffolds by achieving liquid-sintering of β-TCP, thereby tremendously increasing the compressive strength. The ions released from scaffolds pronouncedly inhibited osteoclastogenesis-related gene expressions and multinuclearity of RAW264.7 murine monocyte cells, as well as expressions of early osteogenic makers of mouse bone mesenchymal stem cells (mBMSCs). However, the scaffolds with lower amount of Ga increased cell proliferation and upregulated expression of late osteogenic maker of mBMSCs. This study offers a novel approach to modify the bioceramic scaffolds for bone regeneration under the condition of accelerated bone resorption. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1314-1323, 2019.

Pelvis and femur geometry: Relationships with impact characteristics during sideways falls on the hip

While metrics of pelvis and femur geometry have been demonstrated to influence hip fracture risk, attempts at linking geometry to underlying mechanisms have focused on fracture strength. We investigated the potential effects of femur and pelvis geometry on applied loads during lateral falls on the hip. Fifteen female volunteers underwent DXA imaging to characterize two pelvis and six femur geometric features. Additionally, participants completed low-energy sideways falls on the hip; peak impact force and pressure, contact area, and moment of force applied to the proximal femur were extracted. No geometric feature was significantly associated with peak impact force. Peak moment of force was significantly associated with femur moment arm (p = 0.005). Peak pressure was positively correlated with pelvis width and femur moment arm (p < 0.05), while contact area was negatively correlated with metrics of pelvis width and femur neck length (p < 0.05). This is the first study to link experimental measures of impact loads during sideways falls with image-based skeletal geometry from human volunteers. The results suggest that while skeletal geometry has limited effects on overall peak impact force during sideways falls, it does influence how impact loads are distributed at the skin surface, in addition to the bending moment applied to the proximal femur. These findings have implications for the design of protective interventions (e.g. wearable hip protectors), and for models of fall-related lateral impacts that could incorporate the relationships between skeletal geometry, external load magnitude/distribution, and tissue-level femur loads.

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

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Factors affect stability of intertrochanteric fractures when elderly patients fall

Background

Factors affecting the stability of intertrochanteric fractures when elderly patients fall are few to be reported. In this retrospective study, possible factors were investigated.

Methods

Two hundred and twenty-three consecutive elderly patients (≥65 years) with intertrochanteric fractures due to low energy injuries were studied. Patient age, gender, body mass index (BMI), body weight and height were compared between fractures with stable (AO/OTA type A_1, intact lesser trochanter, 80 patients) and unstable (AO/OTA types A₂, A_3, displaced lesser trochanter or reverse obliquity fractures, 143 patients) types. Statistical approaches with univariate and multivariate analyses were performed.

Results

There was no statistical difference in patient gender, age, body weight or height between patients with stable and unstable fractures in both univariate and multivariate analysis. However, BMI was statistically higher in patients with unstable fractures (22.7 vs 21.4, p = 0.01) in univariate analysis, but without a difference in multivariate analysis (p = 0.07).

Conclusions

Stability of intertrochanteric fractures may be not associated with gender, age, body weight and height or BMI when elderly patients fall. Bone mineral density or impact direction may be other possible contributing factors but requires further proofs.

Clinical Use of Quantitative Computed Tomography-Based Finite Element Analysis of the Hip and Spine in the Management of Osteoporosis in Adults: the 2015 ISCD Official Positions-Part II

The International Society for Clinical Densitometry (ISCD) has developed new official positions for the clinical use of quantitative computed tomography (QCT)-based finite element analysis of the spine and hip. The ISCD task force for QCT reviewed the evidence for clinical applications and presented a report with recommendations at the 2015 ISCD Position Development Conference. Here we discuss the agreed upon ISCD official positions with supporting medical evidence, rationale, controversy, and suggestions for further study. Parts I and III address the clinical use of QCT of the hip, and the clinical feasibility of existing techniques for opportunistic screening of osteoporosis using CT scans obtained for other diagnosis such as colonography was addressed.

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

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

Full-Field Strain Measurement During Mechanical Testing of the Human Femur at Physiologically Relevant Strain Rates

Understanding the mechanical properties of human femora is of great importance for the development of a reliable fracture criterion aimed at assessing fracture risk. Earlier ex vivo studies have been conducted by measuring strains on a limited set of locations using strain gauges (SGs). Digital image correlation (DIC) could instead be used to reconstruct the full-field strain pattern over the surface of the femur. The objective of this study was to measure the full-field strain response of cadaver femora tested at a physiological strain rate up to fracture in a configuration resembling single stance. The three cadaver femora were cleaned from soft tissues, and a white background paint was applied with a random black speckle pattern over the anterior surface. The mechanical tests were conducted up to fracture at a constant displacement rate of 15 mm/s, and two cameras recorded the event at 3000 frames per second. DIC was performed to retrieve the full-field displacement map, from which strains were derived. A low-pass filter was applied over the measured displacements before the crack opened in order to reduce the noise level. The noise levels were assessed using a dedicated control plate. Conversely, no filtering was applied at the frames close to fracture to get the maximum resolution. The specimens showed a linear behavior of the principal strains with respect to the applied force up to fracture. The strain rate was comparable to the values available in literature from in vivo measurements during daily activities. The cracks opened and fully propagated in less than 1 ms, and small regions with high values of the major principal strains could be spotted just a few frames before the crack opened. This corroborates the hypothesis of a strain-driven fracture mechanism in human bone. The data represent a comprehensive collection of full-field strains, both at physiological load levels and up to fracture. About 10,000 points were tracked on each bone, providing superior spatial resolution compared to ∼15 measurements typically collected using SGs. These experimental data collection can be further used for validation of numerical models, and for experimental verification of bone constitutive laws and fracture criteria.

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

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

DIFFERENCES BETWEEN CONTRALATERAL BONES OF THE HUMAN LOWER LIMBS: A MULTISCALE INVESTIGATION

This study addressed side asymmetry between human lower limb long bones.

A multiscale approach was taken to investigate differences between contralateral femurs, tibias and fibulas, at body-level (total-body CT-scans, anatomical dissection), organ-level (volume and moments of areas; structural stiffness and strain distribution in bending and torsions) and tissue-level (mineral density, elastic modulus, hardness).

Because of the large amount of measurements taken, the study was limited to two donors. However, high statistical power within the same donor was achieved thanks to a large number of highly-repeatable measurements. Muscle cross-sections suggested that both donors were right-legged. The right bones had higher structural stiffness (up to +115%, statistically significant, except for the tibia). The right bones also experienced generally lower strain than the contralateral ones (up to -25%, statistically significant). The right bones had larger volume (up to +16%) and moments of area (up to +116%, statistically significant in most cases) than the left ones. Difference in tissue density between contralateral bones (< 7%) was not statistically significant in most cases. Also the differences found in elastic modulus of the femur cortical tissue (2–5%) were not statistically significant. Similarly, tissue hardness in the right bones was only marginally higher than in the contralateral ones (+1% to +4%, not statistically significant). Therefore, it seems that structural differences between contralateral bones associated with laterality are mainly explained by differences in bone quantity (volume) and organization (area moments). Bone tissue quality (density, hardness) seems to give a marginal contribution to structural side asymmetry.

The effect of restriction of dietary calcium on trabecular and cortical bone mineral density in the rats

This study aimed to investigate effects of restricted calcium intake on cortical and trabecular bone density in white rats. Low Ca diet was fed for six weeks, and bone density and bone metabolism parameters were assessed in blood. This study was carried out on 12 male white rats aged 12 weeks (Sprague-Dawley; SD). These rats were bred for 1 week and randomly assigned to the standard calcium diet group (SCa group, n = 6) and the low calcium diet group (LCa group; n = 6). The SCa group was given a modified AIN-93M mineral mix (with 0.5% Ca), which was made by adding calcium to a standard AIN93 diet, and the LCa Group was fed a modified AIN-93 Mineral mix (with 0.1% Ca). Femoral BMD and BMC were measured by DEXA in each rat. After trabecular bone was separated from cortical bone, volumetric bone mineral density (vBMD) was measured using pQCT. Serum Ca and P levels were measured as parameters of bone metabolism, and S-ALP, S-TrACP and-Dpd levels were also measured. The results revealed no significant differences in weight, growth rate, feed consumption and feed efficiency between the two groups before and after calcium-restricted diet (p > .05). No significant differences were also observed in bone length and bone mass between the two groups (p > .05). Although bilateral femoral BMDs were not significantly different between the two groups, bilateral femoral BMCs significantly decreased in the LCa group, compared with the SCa group (p = .023, p = .047). Bilateral cortical MDs were not significantly different between the two groups, either. However, trabecular BMD significantly decreased in the LCa group, compared with the SCa group (p = .041). U-Dpd and S-TrACP levels significantly declined in the LCa group, compared to the SCa group (p = .039, p = .010). There were no significant differences in serum Ca and P levels between the two groups (p > .05). However, a significant decrease in urinary Ca level (p = .001) and a significant increase in urinary P (p = .001) were observed in the LCa group, compared to the Sca group. These findings described that six-week low calcium diet led to decreased trabecular bone density, reduced urinary excretion of Ca and increased urinary excretion of P. As a result, Ca hemeostasis can be maintained.

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±239μɛ. 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.

Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur

Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis.

Skeletal biology over the life span: a view from the surfaces

The biocultural interpretation of skeletal remains is based upon the foundation of skeletal biology. In this review we examine the current state of skeletal biology research outside of the mainstream anthropology literature. The focus is on the structural changes of bone development and growth, and modeling and repair in the four bone surfaces: periosteal, Haversian, endosteal, and trabecular. The pattern of skeletal changes is placed within the framework of the human life span. New perspectives and direction of research on the environmental, biological, and genetic influences on modeling and remodeling processes are discussed chronologically at each bone surface. Implications for biological anthropologists are considered. This approach emphasizes variation in skeletal biology as a dynamic record of development, maturity, and aging.

Finite element modeling of the influence of hand position and bone properties on the Colles' fracture load during a fall

Distal forearm fracture is one of the most frequently observed osteoporotic fractures, which may occur as a result of low energy falls such as falls from a standing height and may be linked to the osteoporotic nature of the bone, especially in the elderly. In order to prevent the occurrence of radius fractures and their adverse outcomes, understanding the effect of both extrinsic and intrinsic contributors to fracture risk is essential. In this study, a nonlinear fracture mechanics-based finite element model is applied to human radius to assess the influence of extrinsic factors (load orientation and load distribution between scaphoid and lunate) and intrinsic bone properties (age-related changes in fracture properties and bone geometry) on the Colles' fracture load. Seven three-dimensional finite element models of radius were created, and the fracture loads were determined by using cohesive finite element modeling, which explicitly represented the crack and the fracture process zone behavior. The simulation results showed that the load direction with respect to the longitudinal and dorsal axes of the radius influenced the fracture load. The fracture load increased with larger angles between the resultant load and the dorsal axis, and with smaller angles between the resultant load and longitudinal axis. The fracture load also varied as a function of the load ratio between the lunate and scaphoid, however, not as drastically as with the load orientation. The fracture load decreased as the load ratio (lunate/scaphoid) increased. Multiple regression analysis showed that the bone geometry and the load orientation are the most important variables that contribute to the prediction of the fracture load. The findings in this study establish a robust computational fracture risk assessment method that combines the effects of intrinsic properties of bone with extrinsic factors associated with a fall, and may be elemental in the identification of high fracture risk individuals as well as in the development of fracture prevention methods including protective falling techniques. The additional information that this study brings to fracture identification and prevention highlights the promise of fracture mechanics-based finite element modeling in fracture risk assessment.

Mechanical testing of bones: the positive synergy of finite-element models and in vitro experiments

Bone biomechanics have been extensively investigated in the past both with in vitro experiments and numerical models. In most cases either approach is chosen, without exploiting synergies. Both experiments and numerical models suffer from limitations relative to their accuracy and their respective fields of application. In vitro experiments can improve numerical models by: (i) preliminarily identifying the most relevant failure scenarios; (ii) improving the model identification with experimentally measured material properties; (iii) improving the model identification with accurately measured actual boundary conditions; and (iv) providing quantitative validation based on mechanical properties (strain, displacements) directly measured from physical specimens being tested in parallel with the modelling activity. Likewise, numerical models can improve in vitro experiments by: (i) identifying the most relevant loading configurations among a number of motor tasks that cannot be replicated in vitro; (ii) identifying acceptable simplifications for the in vitro simulation; (iii) optimizing the use of transducers to minimize errors and provide measurements at the most relevant locations; and (iv) exploring a variety of different conditions (material properties, interface, etc.) that would require enormous experimental effort. By reporting an example of successful investigation of the femur, we show how a combination of numerical modelling and controlled experiments within the same research team can be designed to create a virtuous circle where models are used to improve experiments, experiments are used to improve models and their combination synergistically provides more detailed and more reliable results than can be achieved with either approach singularly.

Direction-specific diaphyseal geometry and mineral mass distribution of tibia and fibula: a pQCT study of female athletes representing different exercise loading types

Bones adapt to prevalent loading, which comprises mainly forces caused by muscle contractions. Therefore, we hypothesized that similar associations would be observed between neuromuscular performance and rigidity of bones located in the same body segment. These associations were assessed among 221 premenopausal women representing athletes in high-impact, odd-impact, high-magnitude, repetitive low-impact, and repetitive nonimpact sports and physically active referents aged 17-40 years. The whole group mean age and body mass were 23 (5) and 63 (9) kg, respectively. Bone cross sections at the tibial and fibular mid-diaphysis were assessed with peripheral quantitative computed tomography (pQCT). Density-weighted polar section modulus (SSI) and minimal and maximal cross-sectional moments of inertia (Imin, Imax) were analyzed. Bone morphology was described as the Imax/Imin ratio. Neuromuscular performance was assessed by maximal power during countermovement jump (CMJ). Tibial SSI was 31% higher in the high-impact, 19% in the odd-impact, and 30% in the repetitive low-impact groups compared with the reference group (P < 0.005). Only the high-impact group differed from the referents in fibular SSI (17%, P < 0.005). Tibial morphology differed between groups (P = 0.001), but fibular morphology did not (P = 0.247). The bone-by-group interaction was highly significant (P < 0.001). After controlling for height, weight, and age, the CMJ peak power correlated moderately with tibial SSI (r = 0.31, P < 0.001) but not with fibular SSI (r = 0.069, P = 0.313). In conclusion, observed differences in the association between neuromuscular performance and tibial and fibular traits suggest that the tibia and fibula experience different loading environments despite their anatomical vicinity.

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

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

Structural behaviour and strain distribution of the long bones of the human lower limbs

Although stiffness and strength of lower limb bones have been investigated in the past, information is not complete. While the femur has been extensively investigated, little information is available about the strain distribution in the tibia, and the fibula has not been tested in vitro. This study aimed at improving the understanding of the biomechanics of lower limb bones by: (i) measuring the stiffness and strain distributions of the different low limb bones; (ii) assessing the effect of viscoelasticity in whole bones within a physiological range of strain-rates; (iii) assessing the difference in the behaviour in relation to opposite directions of bending and torsion. The structural stiffness and strain distribution of paired femurs, tibias and fibulas from two donors were measured. Each region investigated of each bone was instrumented with 8-16 triaxial strain gauges (over 600 grids in total). Each bone was subjected to 6-12 different loading configurations. Tests were replicated at two different loading speeds covering the physiological range of strain-rates. Viscoelasticity did not have any pronounced effect on the structural stiffness and strain distribution, in the physiological range of loading rates explored in this study. The stiffness and strain distribution varied greatly between bone segments, but also between directions of loading. Different stiffness and strain distributions were observed when opposite directions of torque or opposite directions of bending (in the same plane) were applied. To our knowledge, this study represents the most extensive collection of whole-bone biomechanical properties of lower limb bones.

Compressive axial mechanical properties of rat bone as functions of bone volume fraction, apparent density and micro-ct based mineral density

Mechanical testing has been regarded as the gold standard to investigate the effects of pathologies on the structure-function properties of the skeleton. With recent advances in computing power of personal computers, virtual alternatives to mechanical testing are gaining acceptance and use. We have previously introduced such a technique called structural rigidity analysis to assess mechanical strength of skeletal tissue with defects. The application of this technique is predicated upon the use of relationships defining the strength of bone as a function of its density for a given loading mode. We are to apply this technique in rat models to assess their compressive skeletal response subjected to a host of biological and pharmaceutical stimulations. Therefore, the aim of this study is to derive a relationship expressing axial compressive mechanical properties of rat cortical and cancellous bone as a function of equivalent bone mineral density, bone volume fraction or apparent density over a range of normal and pathologic bones. We used bones from normal, ovariectomized and partially nephrectomized animals. All specimens underwent micro-computed tomographic imaging to assess bone morphometric and densitometric indices and uniaxial compression to failure. We obtained univariate relationships describing 71-78% of the mechanical properties of rat cortical and cancellous bone based on equivalent mineral density, bone volume fraction or apparent density over a wide range of density and common skeletal pathologies. The relationships reported in this study can be used in the structural rigidity analysis introduced by the authors to provide a non-invasive method to assess the compressive strength of bones affected by pathology and/or treatment options.

The Effects of Treadmill Exercise Training on Hip Bone Density and Tibial Bone Geometry in Stroke Survivors: A Pilot Study

Background. Individuals with stroke often sustain bone loss on the hemiparetic side and are prone to fragility fractures. Exercise training may be a viable way to promote bone mineral density (BMD) and geometry in this population. Objective. This was a pilot study to evaluate the effects of a 6-month treadmill exercise program on hip BMD and tibial bone geometry in chronic stroke survivors. Methods. Twenty-one individuals with chronic stroke, with a mean age of 64.5 years and mean poststroke duration of 8.3 years participated in the study. The treatment group underwent a treadmill gait exercise program (two 1-hour sessions per week for 6 months), whereas the control group participated in their usual self-selected activities in the community. The primary outcomes were hip BMD and bone geometry of the midshaft tibia on the paretic side, whereas the secondary outcomes were gait velocity, endurance, leg muscle strength, balance self-efficacy, and physical activity level. Mann-Whitney U tests were used to compare the change in all outcome variables between the 2 groups after treatment. Results. Significant between-group differences in change scores of tibial cortical thickness ( P = .016), endurance ( P = .029), leg muscle strength on the paretic side ( P < .001) and nonparetic side ( P < .001), balance self-efficacy ( P = .016), and physical activity level ( P = .023) were found. Conclusion . The treadmill exercise program induced a modest improvement in tibial bone geometry in individuals with chronic stroke. Further studies are required to explore the optimal training protocol for promoting favorable changes in bone parameters following stroke.

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

INTRODUCTION

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

METHODS

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

RESULTS AND CONCLUSIONS

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

More aggravated osteoporosis in lateral trochanter compared to femoral neck with age: contributing age difference between inter-trochanteric and femoral neck fractures in elderly patients

In the medical literature, elderly patients with inter-trochanteric fractures are considered older than those with femoral neck fractures, but the reason for this age-related difference remains unclear. Inconsistent bone mass re-distribution with age in both regions was hypothesised and the change in bone mineral density (BMD) was studied. This study aims to investigate another possible pathomechanism of reducing bone strength in the proximal femur with increasing age. The findings might help in developing a better method for preventing osteoporotic hip fractures.

PATIENTS AND METHODS

In the BMD study, 400 consecutive female patients were divided into eight groups, comprising 50 individuals each. Except for the first group (16-20 years), all other groups were divided by 10-year age increments up to 90 years. Relative BMD change with age in different regions in each group was compared.

RESULTS

The BMD ratio of the lateral trochanter to the neck gradually reduced with age, whereas that of the medial trochanter to the neck gradually increased. The comparisons were statistically significant (p<0.001 in both cases).

CONCLUSION

One important predisposing factor to affect patients with inter-trochanteric fractures older than those with femoral neck fractures may be that the BMD is further lowered in the lateral trochanter compared to the femoral neck with age. It may be caused by lack of compressive loads in the lateral trochanter in daily activity. All devices which may increase bone mass in the lateral trochanter, theoretically, may be helpful in lowering the incidence of hip fractures.

Stress shielding and stress concentration of contemporary epiphyseal hip prostheses

After the first early failures, proximal femoral epiphyseal replacement is becoming popular again. Prosthesis-to-bone load transfer is critical for two reasons: stress shielding is suspected of being responsible for a number of failures of early epiphyseal prostheses; stress concentration is probably responsible of the relevant number of early femoral neck fractures in resurfaced patients. The scope of this work was to experimentally investigate the load transfer of a commercial epiphyseal prosthesis (Birmingham Hip Replacement (BHR)) and an innovative prototype proximal epiphyseal replacement. To investigate bone surface strain, ten cadaveric femurs were instrumented with 15 triaxial strain gauges. In addition the cement layer of the prototype was instrumented with embedded gauges to estimate the strain in the adjacent trabecular bone. Six different loading configurations were investigated, with and without muscles. For the BHR prosthesis, significant stress shielding was observed on the posterior side of the head-neck region (the strain was halved); a pronounced stress concentration was observed on the anterior surface (up to five times in some specimens); BHR was quite sensitive to the different loading configurations. For the prototype, the largest stress shielding was observed in the neck region (lower than the BHR; alteration less than 20 per cent); some stress concentration was observed at the head region, close to the rim of the prosthesis (alteration less than 20 per cent); the different loading configurations had similar effects. Such large alterations with respect to the pre-operative conditions were found only in regions where the strain level was low. Conversely, alterations were moderate where the strain was higher. Thus, prosthesis-to-bone load transfer of both devices has been elucidated; the prototype preserved a stress distribution closer to the physiological condition.

Cortical and trabecular bone in the femoral neck both contribute to proximal femur failure load prediction

We examined the contributions of femoral neck cortical and trabecular bone to proximal femur failure load. We found that trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for total bone size and cortical bone mineral content or cortical area.

INTRODUCTION

The relative contribution of femoral neck trabecular and cortical bone to proximal femur failure load is unclear.

OBJECTIVES

Our primary objective was to determine whether trabecular bone mineral density (TbBMD) contributes to proximal femur failure load after accounting for total bone size and cortical bone content. Our secondary objective was to describe regional differences in the relationship among cortical bone, trabecular bone, and failure load within a cross-section of the femoral neck.

MATERIALS AND METHODS

We imaged 36 human cadaveric proximal femora using quantitative computed tomography (QCT). We report total bone area (ToA), cortical area (CoA), cortical bone mineral content (CoBMC), and TbBMD measured in the femoral neck cross-section and eight 45 degrees regions. The femora were loaded to failure.

RESULTS AND OBSERVATIONS

Trabecular bone mineral density explained a significant proportion of variance in failure load after accounting for ToA and then either CoBMC or CoA respectively. CoBMC contributed significantly to failure load in all regions of the femoral neck except the posterior region. TbBMD contributed significantly to failure load in all regions of the femoral neck except the inferoanterior, superoposterior, and the posterior regions.

CONCLUSION

Both cortical and trabecular bone make significant contributions to failure load in ex vivo measures of bone strength.

Strain distribution in the proximal human femoral metaphysis

There is significant interest in the stress—strain state in the proximal femoral metaphysis, because of its relevance for hip fractures and prosthetic replacements. The scope of this work was to provide a better understanding of the strain distribution, and of its correlation with the different directions of loading, and with bone quality. A total of 12 pairs of human femurs were instrumented with strain gauges. Six loading configurations were designed to cover the range of directions spanned by the hip joint force. Inter-specimen variability was reduced if paired specimens were considered. The principal strain magnitude varied greatly between loading configurations. This suggests that different loading configurations need to be simulated in vitro. The strain magnitude varied between locations but, on average, was compatible with the strain values measured in vivo. The strain magnitudes and the direction of principal tensile strain in the head and neck were compatible with the spontaneous fractures of the proximal femur reported in some subjects. The principal tensile strain was significantly larger where the cortical bone was thinner; the compressive strain was larger where the cortical bone was thicker. The direction of the principal strain varied significantly between measurement locations but varied little between loading configurations. This suggests that the anatomy and the distribution of anisotropic material properties enable the proximal femur to respond adequately to the changing direction of daily loading.

Femoral geometry as a risk factor for osteoporotic hip fracture in men and women

Osteoporotic hip fracture is associated with high mortality and morbidity and often results in a loss of mobility and independence. Osteoporosis is diagnosed by measuring Bone Mineral Density (BMD), a measure of the amount of mineral in a bone. Although BMD continues to serve well it does not fully account for bone strength and only partially accounts for the risk of hip fracture. The shape and structure of the proximal femur also help to determine how forces act in the hip in a fall and their measurement can aid the prediction of hip fracture. This review examines the link between simple geometrical measures of the proximal femur and hip fracture, or bone strength. It will explore how they relate to each other and to anthropometric factors such as sex, height, weight and age. Limitations in these measures will be identified and new methods of analysis reviewed that encompass many different aspects of the shape of the femur. These new methods show great promise for improving the prediction of fracture risk in the future.

Experimental hip fracture load can be predicted from plain radiography by combined analysis of trabecular bone structure and bone geometry

Computerized analysis of the trabecular structure was used to test whether femur failure load can be estimated from radiographs. The study showed that combined analysis of trabecular bone structure and geometry predicts in vitro failure load with similar accuracy as DXA.

INTRODUCTION

Since conventional radiography is widely available with low imaging cost, it is of considerable interest to discover how well bone mechanical competence can be determined using this technology. We tested the hypothesis that the mechanical strength of the femur can be estimated by the combined analysis of the bone trabecular structure and geometry.

METHODS

The sample consisted of 62 cadaver femurs (34 females, 28 males). After radiography and DXA, femora were mechanically tested in side impact configuration. Fracture patterns were classified as being cervical or trochanteric. Computerized image analysis was applied to obtain structure-related trabecular parameters (trabecular bone area, Euler number, homogeneity index, and trabecular main orientation), and set of geometrical variables (neck-shaft angle, medial calcar and femoral shaft cortex thicknesses, and femoral neck axis length). Multiple linear regression analysis was performed to identify the variables that best explain variation in BMD and failure load between subjects.

RESULTS

In cervical fracture cases, trabecular bone area and femoral neck axis length explained 64% of the variability in failure loads, while femoral neck BMD also explained 64%. In trochanteric fracture cases, Euler number and femoral cortex thickness explained 66% of the variability in failure load, while trochanteric BMD explained 72%.

CONCLUSIONS

Structural parameters of trabecular bone and bone geometry predict in vitro failure loads of the proximal femur with similar accuracy as DXA, when using appropriate image analysis technology.

Fuzzy logic structure analysis of trabecular bone of the calcaneus to estimate proximal femur fracture load and discriminate subjects with and without vertebral fractures using high-resolution magnetic resonance imaging at 1.5 T and 3 T

Newly developed fuzzy logic-derived structural parameters were used to characterize trabecular bone architecture in high-resolution magnetic resonance imaging (HR-MRI) of human cadaver calcaneus specimens. These parameters were compared to standard histomorphological structural measures and analyzed concerning performance in discriminating vertebral fracture status and estimating proximal femur fracture load. Sets of 60 sagittal 1.5 T and 3.0 T HR-MRI images of the calcaneus were obtained in 39 cadavers using a fast gradient recalled echo sequence. Structural parameters equivalent to bone histomorphometry and fuzzy logic-derived parameters were calculated using two chosen regions of interest. Calcaneal, spine, and hip bone mineral density (BMD) measurements were also obtained. Fracture status of the thoracic and lumbar spine was assessed on lateral radiographs. Finally, mechanical strength testing of the proximal femur was performed. Diagnostic performance in discriminating vertebral fracture status and estimating femoral fracture load was calculated using regression analyses, two-tailed t-tests of significance, and receiver operating characteristic (ROC) analyses. Significant correlations were obtained at both field strengths between all structural and fuzzy logic parameters (r up to 0.92). Correlations between histomorphological or fuzzy logic parameters and calcaneal BMD were mostly significant (r up to 0.78). ROC analyses demonstrated that standard structural parameters were able to differentiate persons with and without vertebral fractures (area under the curve [A(Z)] up to 0.73). However, none of the parameters obtained in the 1.5-T images and none of the fuzzy logic parameters discriminated persons with and without vertebral fractures. Significant correlations were found between fuzzy or structural parameters and femoral fracture load. Using multiple regression analysis, none of the structural or fuzzy parameters were found to add discriminative value to BMD alone. In summary significant correlations were obtained at both field strengths between all structural and fuzzy logic parameters. However, fuzzy logic-based calcaneal parameters were not well suited for vertebral fracture discrimination. Although significant correlations were found between fuzzy or structural parameters and femoral fracture load, multiple regression analysis showed limited improvement for estimating femoral failure load in addition to femoral BMD alone. Local femoral measurements are still needed to estimate femoral bone strength. Overall, parameters obtained at 3.0 T performed better than those at 1.5 T.

Tibial geometry is associated with failure load ex vivo: a MRI, pQCT and DXA study

We studied the relations between bone geometry and density and the mechanical properties of human cadaveric tibiae. Bone geometry, assessed by MRI and pQCT, and bone density, assessed by DXA, were significantly associated with bone's mechanical properties. However, cortical density assessed by pQCT was not associated with mechanical properties.

INTRODUCTION

The primary objective of this study was to determine the contribution of cross-sectional geometry (by MRI and pQCT) and density (by pQCT and DXA) to mechanical properties of the human cadaveric tibia.

METHODS

We assessed 20 human cadaveric tibiae. Bone cross-sectional geometry variables (total area, cortical area, and section modulus) were measured with MRI and pQCT. Cortical density and areal BMD were measured with pQCT and DXA, respectively. The specimens were tested to failure in a four-point bending apparatus. Coefficients of determination between imaging variables of interest and mechanical properties were determined.

RESULTS

Cross-sectional geometry measurements from MRI and pQCT were strongly correlated with bone mechanical properties (r(2) range from 0.55 to 0.85). Bone cross-sectional geometry measured by MRI explained a proportion of variance in mechanical properties similar to that explained by pQCT bone cross-sectional geometry measurements and DXA measurements.

CONCLUSIONS

We found that there was a close association between geometry and mechanical properties regardless of the imaging modality (MRI or pQCT) used.

Quantitative trait locus that determines the cross-sectional shape of the femur in SAMP6 and SAMP2 mice

We segregated a QTL on chromosome 11 that affects femoral cross-sectional shape during growth by generating a congenic strain and an additional 16 subcongenic strains of the senescence-accelerated mouse strain, SAMP6. The QTL region was narrowed down to a 10.0-Mbp region.

INTRODUCTION

Genetic background is known to affect bone characteristics. However, little is known about how polymorphic genes modulate bone shape. In a previous study using SAMP2 and SAMP6 mice, we reported a quantitative trait locus (QTL) on chromosome (Chr) 11 that had significant linkage to peak relative bone mass in terms of cortical thickness index (CTI) in male mice. We named it Pbd1. Here we aimed to clarify the effects of Pbd1 on skeletal phenotype in male mice and to narrow down the QTL region.

MATERIALS AND METHODS

We generated a congenic strain named P6.P2-Pbd1(b), carrying a 39-cM SAMP2-derived Chr11 interval on a SAMP6 genetic background. Sixteen subcongenic strains with smaller overlapping intervals on the SAMP6 background were generated from P6.P2-Pbd1(b) to narrow the region of interest. The effects of Pbd1 on bone properties were determined. Gene expression analysis of all candidate genes in Pbd1 was performed using real-time RT-PCR.

RESULTS

The CTI of strain P6.P2-Pbd1(b) at 16 wk was higher than that of SAMP6. This was not caused by differences in cortical thickness but by cross-sectional shape. Morphological analysis by microCT revealed that the femoral cross-sectional shape of P6.P2-Pbd1(b) (and the other subcongenic strains with higher CTI or bone area fraction [BA/TA]) was more compressed anteroposteriorly than that of SAMP6, which was associated with superior mechanical properties. This feature was formed during bone modeling up to 16 wk of age. Subcongenic strains with a higher CTI showed significant increases in endocortical mineral apposition rate and significant reductions in periosteal mineral apposition rate at 8 wk compared with those of the SAMP6. The Pbd1 locus was successfully narrowed down to a 10.0-Mbp region, and the expression analysis suggested a candidate gene, Cacng4.

CONCLUSIONS

The Pbd1 affects femoral cross-sectional shape by regulating the rate of endocortical and periosteal bone formation of the femur during postnatal growth.

In vitro replication of spontaneous fractures of the proximal human femur

Spontaneous fractures (i.e. caused by sudden loading and muscle contraction, not by trauma) represent a significant percentage of proximal femur fractures. They are particularly relevant as may occur in elderly (osteoporotic) subjects, but also in relation to epiphyseal prostheses. Despite its clinical and legal relevance, this type of fracture has seldom been investigated. Studies concerning spontaneous fractures are based on a variety of loading scenarios. There is no evidence, nor consensus on the most relevant loading scenario. The aim of this work was to develop and validate an experimental method to replicate spontaneous fractures in vitro based on clinically relevant loading. Primary goals were: (i) repeatability and reproducibility, (ii) clinical relevance. A validated numerical model was used to identify the most critical loading scenario that can lead to head-neck fractures, and to determine if it is necessary to include muscle forces when the head-neck region is under investigation. The numerical model indicated that the most relevant loading scenario is when the resultant joint force is applied to the head at 8 degrees from the diaphysis. Furthermore, it was found that it is not essential to include the muscles when investigating head-neck fractures. The experimental setup was consequently designed. The procedure included high-speed filming of the fracture event. Clinically relevant fracture modes were obtained on 10 cadaveric femurs. Failure load should be reported as a fraction of donor's body-weight to reduce variability. The proposed method can be used to investigate the reason and mechanism of failure of natural and operated proximal femurs.

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

INTRODUCTION

Magnetic resonance imaging (MRI) is a promising medical imaging technique that we used to assess femoral neck cortical geometry.

OBJECTIVES

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.

MATERIALS AND METHODS

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).

RESULTS AND OBSERVATIONS

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).

CONCLUSION

We report that MRI holds considerable promise for measuring cortical bone geometry in the femoral neck and for predicting strength at the proximal femur.

Bone geometry and skeletal fragility

Although low bone mineral density is among the strongest risk factors for fracture, a number of clinical studies have demonstrated the limitations of bone mineral density measurements in assessing fracture risk and monitoring the response to therapy. These observations have brought renewed attention to the broader array of factors that influence skeletal fragility, including bone size, shape, and microarchitecture. This article reviews the relationship between bone geometry and skeletal fragility, focusing on the impact of bone geometry on bone strength and fracture risk. It also reviews recent data on the effect of osteoporosis therapies on femoral geometry. It is clear that characteristics of a bone's size and shape strongly influence its biomechanical strength, but there is no consensus as to the geometric parameters that improve prediction of fracture risk. Recent data from hip structure analysis indicate that antiresorptive and anticatabolic treatments alter femoral geometry, but this observation depends on several assumptions that have not been tested in subjects treated with osteoporosis therapies. Current knowledge is limited, in part, by the predominant use of two-dimensional techniques to assess bone geometry. Additional studies that incorporate three-dimensional imaging are needed to better define the relationship between bone geometry and skeletal fragility, and to establish the clinical utility of bone geometry measurements.