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Due to the adverse impacts of hip fractures on patients’ lives, it is crucial to enhance the identification of people at high risk through accessible clinical techniques. Reconstructing the 3D geometry and BMD distribution of the proximal femur could be beneficial in enhancing hip fracture risk predictions; however, it is associated with a high computational burden. It is also not clear whether it provides a better performance than 2D model analysis. Therefore, the purpose of this study was to compare the 2D and 3D model reconstruction’s ability to predict hip fracture risk in a clinical population of patients. The DXA scans and CT scans of 16 cadaveric femurs were used to create training sets for the 2D and 3D model reconstruction based on statistical shape and appearance modeling. Subsequently, these methods were used to predict the risk of sustaining a hip fracture in a clinical population of 150 subjects (50 fractured, and 100 non-fractured) that were monitored for five years in the Canadian Multicentre Osteoporosis Study. 3D model reconstruction was able to improve the identification of patients who sustained a hip fracture more accurately than the standard clinical practice (by 40%). Also, the predictions from the 2D statistical model didn’t differ significantly from the 3D ones (p > 0.76). These results indicated that to enhance hip fracture risk prediction in clinical practice implementing 2D statistical modeling has comparable performance with lower associated computational load.

A new technique to enhance hip fracture risk prediction in older adults was presented and assessed. The new method dramatically improved prediction at high specificity levels using only a standard clinical diagnostic scan. This has the potential to be implemented in clinical practice to enhance patient fragility diagnosis. Diagnosis of osteoporosis is based on the measurement of bone mineral density (BMD) using dual-energy X-ray absorptiometry (DXA) scans. However, studies have shown this to be insufficient to accurately predict hip fractures. Therefore, complementary methods are needed to enhance hip fracture risk prediction to identify vulnerable patients. Hip DXA scans were obtained for 192 subjects from the Canadian Multicenter Osteoporosis Study (CaMos), 50 of whom had experienced a hip fracture within 5 years of the scan. 2D statistical shape and appearance modeling was performed to account for the effect of the femur’s geometry and BMD distribution on hip fracture risk. Statistical shape modeling (SSM), and statistical appearance modeling (SAM) were also used separately to predict the fracture risk based solely on the femur’s geometry and BMD distribution, respectively. Combined with BMD, age, and body mass index (BMI), logistic regression was performed to estimate the fracture risk over the 5-year period. Using the new technique, hip fractures were correctly predicted in 78% of cases compared with 36% when using the T-score. The accuracy of the prediction was not greatly reduced when using SSM and SAM (78% and 74% correct, respectively). Various geometric and BMD distribution traits were identified in the fractured and non-fractured groups. 2D SSAM can dramatically improve hip fracture prediction at high specificity levels and estimate the year of the impending fracture using standard clinical images. This has the potential to be implemented in clinical practice to estimate hip fracture risk.

Each year in the US more than 300,000 older adults suffer from hip fractures. While protective measures exist, identification of those at greatest risk by DXA scanning has proved inadequate. This study proposed a new technique to enhance hip fracture risk prediction by accounting for many contributing factors to the strength of the proximal femur. Twenty-two isolated cadaveric femurs were DXA scanned, 16 of which had been mechanically tested to failure. A function consisting of the calculated modes from the statistical shape and appearance modeling (to consider the shape and BMD distribution), homogeneity index (representing trabecular quality), BMD, age and sex of the donor was created in a training set and used to predict the fracture load in a test group. To classify patients as "high risk" or "low risk", fracture load thresholds were investigated. Hip fracture load estimation was significantly enhanced using the new technique in comparison to using t-score or BMD alone (average R² of 0.68, 0.32, and 0.50, respectively) (P 0.05). Using a fracture cut-off of 3400 N correctly predicted risk in 94% of specimens, a substantial improvement over t-score classification (38%). Ultimately, by identifying patients at high risk more accurately, devastating hip fractures can be prevented through applying protective measures.

Ballistic shields are used by military and police members in dangerous situations to protect the user against threats such as gunfire. When struck, the shield material deforms to absorb the incoming kinetic energy of the projectile. If the rapid back-face deformation contacts the arm, it can potentially impart a large force, leading to injury risk, termed behind armor blunt trauma (BABT). This work characterized the loading profiles due to the contact between the deforming back-face of the shield and the arm using a modified upper extremity anthropomorphic test device (ATD). This ATD measured forces at the hand, wrist, forearm, and elbow to compare the locational effects of the force transfer for future investigations of fracture risk. Two composite ballistic shields, both with the same ballistic protection rating, were investigated and had statistically different responses to the same impact conditions, indicating a further need for shield safety evaluation. Additionally, ballistic force curves were compared among stand-off distances, defined as the distance between the back-face of the shield and the front of the force sensor, where the peak impact force significantly decreased with increased stand-off. This study presents the first highly instrumented ATD upper limb capable of evaluating BABT and characterization of these loading profiles. This work demonstrates the importance of realistic boundary conditions as loading varies by anatomical location. Stand-off distance is an effective method to reduce loading and should be considered in future shield design iterations and standards that are developed using this device.

Foot injuries as a result of automotive collisions are frequent and impactful. Anthropomorphic test devices (ATDs), used to assess injury risk during impact scenarios such as motor vehicle collisions, typically assess risk of foot/ankle injuries by analyzing data in tibia load cells. The peak axial force and the tibia index are metrics commonly used to evaluate risk of injury to the lower extremity but do not directly account for injury risk to the foot, or the risk of injury associated with out-of-position loading. Two ATDs, the Hybrid III lower leg and the Military Lower Extremity, were exposed to axial impacts at seven different ankle postures. An array of piezoresistive sensors located on the insole of a boot was employed during these tests to assess the load distribution variations among postures and between ATD models on the plantar surface of the foot. Both posture and ATD model affected the load distribution on the foot, highlighting the need for regional injury risk assessments in this vulnerable anatomical region. The increase in forefoot loading during plantarflexion was not reflected in the standard industry metrics of peak axial force or tibia index, suggesting that increased fracture risk to the forefoot would not be detected. The variations in load distribution between the models could also alter injury risk assessment in frontal collisions based on differences in attenuation. These data could be used for regional foot injury assessment and to inform the design of an improved ATD foot.

Comminuted proximal tibia fractures are an ongoing surgical challenge. This "proof of concept" study is the first step in designing a new percutaneous plate for this injury under toe-touch weight-bearing as prescribed after surgery. Finite element simulations generated design curves for overall stiffness, bone and implant stress, and interfragmentary motion using 3 fixations (no, 1, or 2 "kickstand" (KS) screws across the fracture gap) over a range of plate elastic moduli (E

This study presents a new protocol for preparing bone samples for scanning electron microscopy (SEM) using a room temperature ionic liquid (RTIL) treatment method. RTIL-based solutions can be adopted as an alternative to lengthy and laborious traditional means of preparation for SEM due to their unique low-vapour pressure and conductive properties. Applied to biological samples, RTILs can be used quickly and efficiently to observe hydrated, unfixed structures in typical SEM systems. This first-time feasibility study of the optimization of this protocol for bone was explored through various SEM modalities using two distinct ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMI][BF4]) and 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMI][BF4]), at varying concentrations of 5, 10, and 25% v/v in aqueous solution through an addition-based method. Based on qualitative observations in the SEM, a 60-second solution addition treatment of 10% v/v [BMI][BF4] performed the best in imaging hydrated, unfixed bone samples, resulting in minimal charge buildup and no solution pooling on the surface. The treatment was applied effectively to a variety of bone samples, notably flat and polished, as well as highly topographical bone fracture surfaces of both healthy and osteoporotic human bone samples. In comparison to conventionally dehydrated bone, the RTIL treatment better preserved the natural bone structure, resulting in minimal microcracking in observed structures.

Various bone abnormalities, including osteoporosis, have been associated with chronic arsenic and cadmium exposure in experimental animal models, but information regarding the bone pathology of wild population of small mammals breeding in contaminated environment is limited. This present study was conducted to comparatively assess the prevalence and pattern of skeletal abnormalities in free ranging snowshoe hares inhabiting an area heavily contaminated by arsenic and other trace metals, near the vicinity of the abandoned Giant mine, and in a reference location approximately 20km from the city of Yellowknife, Northwest Territories, Canada. The femur and vertebrae of snowshoe hares from the mine area and reference location were subjected to bone densitometry examination and biomechanical testing using dual energy X-ray absorptiometry (DXA) and 3-point bending test. t-test results indicated that femoral densitometry parameters such as bone mineral density (BMD) (p=0.5), bone mineral content (BMC) (p=0.675), bone area (BA) (p=0.978) and tissue area (TA) (p=0.549) were not significantly different between locations. All densitometry parameters of the vertebrae (BMD, BA and TA) differed between locations (p

The lower legs are at risk of substantial injury during events such as frontal automotive crashes and antivehicular mine blasts. Loading to occupants can be assessed using an instrumented anthropomorphic test device (ATD), whose measurements can be compared to established injury criteria. NATO's AEP-55 STANAG 4569 recognizes two surrogates for lower leg injury assessments from impacts with intruding floor pans resulting from underbelly blast loads; (1) the rigid Hybrid III instrumented lower leg, and; (2) the compliant MILitary Lower eXtremity (MIL-LX). The established injury criterion for the Hybrid III leg specifies a maximum lower tibia compressive load of 5.4 kN, whereas the MIL-LX limit is 2.6 kN measured at the upper tibia for similar injury severity levels. The difference in compliance between the two legs could affect the evaluation of protection levels, resulting in an over- or under-estimation of the force attenuation of energy attenuating (EA) floor mats.The responses of the two lower leg surrogates were evaluated at impact velocities up to 12 m/s, representing floor intrusions during antivehicle mine blasts. An air cannon was used to accelerate a rigid or padded floor plate into the sole of the surrogate lower legs, loading them axially, in order to assess the protective capability of commercial EA floor mats. The peak load from the lower and upper load cells in the Hybrid III and MIL-LX legs were compared to identify at what point their respective injury criteria would be exceeded in both the padded and unpadded conditions.Comparisons of the surrogate legs' responses resulted in different evaluations of risk, with the Hybrid III leg exceeding its limit at an impact speed of 6.0 m/s, and the MIL-LX exceeding its limit at 5.5 m/s (for tests including an EA product). Furthermore, the inclusion of an EA mat had a greater relative protective effect on the Hybrid III than the MIL-LX leg, with padding reducing the force to 17 to 34% of the unpadded condition for the Hybrid III, versus 67 to 89% of the unpadded condition for the MIL-LX. The load reduction was found to be velocity dependent for both surrogates.These results indicate that the two surrogates are not equivalent in their assessment of protective capability. Therefore, the selection of ATD leg for testing of EA mats (and other protective devices) will influence the evaluation of these systems, and more robust metrics are required to identify which is the most appropriate surrogate for evaluating injury to the lower limb.

© 2020, © 2020 Taylor & Francis Group, LLC. Objective: The tibia is the most commonly fractured long bone in a pedestrian-vehicle collision. The standard injury assessment tool is the “legform,” a device that mimics the human lower limb under impact loads. These devices are designed to identify the impact load that will cause the onset of injury, rather than replicate the type and severity of fracture. Thus, this study is the first to determine if composite tibias made by Sawbones (Pacific Research Labs, Vashon, WA, USA) designed for orthopedic biomechanics research, could also potentially be used for traffic safety research by simulating both the damage tolerance of human cadaveric tibias for peak force and bending moment and the fracture patterns themselves, thereby more accurately predicting injury type during real-world pedestrian-vehicle collisions. Methods: Synthetic tibias (n = 6) and human cadaveric tibias (n = 6) were impacted at midshaft at 8.3 m/s (i.e., 30 km/h) under 3-point bending using a pneumatic impacting apparatus. Fracture force, bending moment, and fracture patterns were compared between the two groups, and Weibull survivability curves generated for force and moment results, to identify injury risk thresholds. Results: There was no difference for synthetic vs. cadaveric tibias regarding impact force (4271+/-938 N vs. 4889+/-993 N, p = 0.44) or bending moment at fracture (275+/-64 Nm vs. 302+/-107 Nm, p = 0.69). Force-time curves for all tibias were similar in shape based on the first three Principal Components (p > 0.14). Weibull survivability curves had differences in shape and in the 10% risk of fracture limits, with force thresholds of 2873 N for the synthetic vs. 3386 N for the cadaveric, and bending moment limits of 180 Nm for the synthetic compared to 157 Nm for the cadaveric. All fracture patterns were clinically realistic, but not consistent between groups. The coefficient of variation for synthetic tibias was >0.2 for both peak force and bending moment, which precludes their use as a reproducible test surrogate for injury prediction. Conclusions: Synthetic composite tibias offer the potential for developing a frangible test surrogate, and matched cadaveric response in several respects. However, the repeatability was not high enough for them to be used in their present form for injury prediction.

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

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.

Environmental loadings of polycyclic aromatic compounds (PACs) and trace elements are increasing in areas with marked oil and gas extraction, such as in the Athabasca oil sands region, Alberta, Canada. Some of these chemicals are recognized as potent endocrine disrupting compounds (EDCs). The impacts of co-exposure to PACs and metals on free-ranging wildlife is of considerable concern. River otters (Lontra canadensis) are sentinel species of aquatic ecosystem health. The baculum (penile bone) is an important part of the reproductive system in otters that ensures successful copulation. Although baculum health is critical to male reproductive success and is sensitive to exposure to EDCs, there is no information available regarding the impact of PAC and metal exposures on measures of baculum health. River otter baculum and livers were dissected from carcasses obtained from the fur trade. Trace element and PAC analyses were carried out in liver with matching baculums subjected to dimensional analysis, bone mineral density (BMD) and mechanical loading testing. Trace elements and select PACs exhibited both protective and deleterious effects on baculum bone health metrics. Alkylated four ring PACs were negatively associated with baculum bone material properties (ex: C4-Chrysene and C4-pyrene). The same compounds have been shown to exhibit strong anti-androgenic activities. Few comparable studies exist related to contamination and adverse effects of PACs in wild terrestrial mammals. Baculum health metrics may be an important tool to include in biomonitoring studies as to date, there are limited means to assess male reproductive performance in wildlife biomonitoring programs.

Osteoporosis is a disease prevalent in older adults, characterized by high porosity in bone and subsequent decrease in fracture resistance. This demographic is also the population that most frequently receives devices such as hip implants. However, high porosity complicates surgery and reduces the fixation and effectiveness of orthopaedic devices, which are typically designed using cadaveric specimens from the general population. Synthetic bones are also used in the design of such devices but need to represent the properties of the patient population. Thus, the mechanical response of two iterations of novel synthetic femurs were evaluated for their ability to represent osteoporotic cadaveric specimens and were tested and compared against cadaveric specimens across four loading modes. The first iteration had reduced density and wall thickness compared to standard models and was typically too rigid or too stiff to be a feasible alternative to cadaveric specimens. The second iteration, with similarly reduced wall thickness and further reduced density, was quite representative, with no statistical differences identified against the cadaveric specimens in any loading mode, except in screw pullout. Such a model can provide a foundation for the development of orthopaedic devices better suited to osteoporotic bone, potentially improving surgical outcomes, reducing medical expense, and improving quality of life for patients.

Anthropomorphic test devices (ATDs) are used to assess real injury risk to occupants of vehicles during injurious events. In the lower leg, values from load cells are compared to injury criteria developed in cadaveric studies. These criteria are typically developed with the leg in a neutral posture, whereas the ATD may assume a wide range of postures during safety evaluation tests. The degree to which the initial posture of an ATD has an effect on the measured forces and moments in the lower leg is unknown.A Hybrid III ATD lower leg was impacted in a range of postures under conditions representing a crash test, and peak axial force and adjusted tibia index injury measures were evaluated. Ankle posture was varied in 5° increments using a custom-made footplate, and dorsi/plantarflexion (20° DF to 20° PF) and in/eversion (20° IV to 5° EV) were evaluated. Tibia angle was also varied (representing knee flexion/extension) by ±10° from neutral.Peak axial force was not affected by ankle flexion or tibia angulation. Adjusted tibia index was lowest for plantarflexion, as well as for tibia angles representative of knee extension. Both peak axial force and adjusted tibia index were lowest for postures of great inversion and were highest in neutral or near-neutral postures.The range of postures tested herein spanned published injury criteria and thus would have made the difference between pass and fail in a safety evaluation. In/eversion had the largest influence on injury metrics, likely due to the change in axial stiffness and altered impact durations in these postures. Results suggest increased injury risk at neutral or near-neutral postures, whereas previous cadaveric studies have suggested that in/eversion does not influence injury risk. It is unclear whether the ATD appropriately represents the natural lower leg for impacts in out-of-position testing. Great care must be taken when initially positioning ATDs for safety evaluations, because small perturbations in posture were shown herein to have large effects on the measured injury risk using this tool.

Lower leg injuries commonly occur in frontal automobile collisions, and are associated with high disability rates. Accurate methods to predict these injuries must be developed to facilitate the testing and improvement of vehicle safety systems. Anthropomorphic test devices (ATDs) are often used to assess injury risk by mimicking the behavior of the human body in a crash while recording data from sensors at discrete locations, which are then compared to established safety limits developed by cadaveric testing. Due to the difference in compliance of cadaveric and ATD legs, the force dissipating characteristics of footwear, and the lack of direct measurement of injury risk to the foot and ankle, a novel instrumented insole was developed that could be applied equally to all specimens both during injury limit generation and during safety evaluation tests. An array of piezoresistive sensors were calibrated over a range of speeds using a pneumatic impacting apparatus, and then applied to the insole of a boot. The boot was subsequently tested and compared to loads measured using ankle and toe load cells in an ATD, and found to have an average error of 10%. The sensors also provided useful information regarding the force distribution across the sole of the foot during an impact, which may be used to develop regional injury criteria. This work has furthered the understanding of lower leg injury prediction and developed a tool that may be useful in developing accurate injury criteria in the future for the foot and lower leg.

Axial impacts to the lower leg during debilitating events such as frontal automotive collisions and military underbody blasts can cause significant injuries to the tibia. Several studies have conducted axial impact tests to determine the injury limits of the lower leg, mostly focused on automotive intrusions, resulting in an established force criterion for injury assessments. Due to the viscoelastic properties of bone, it remains unclear whether results from automotive experiments can be applied to higher-rate military blasts. Twelve male isolated cadaveric tibias (from six pairs, mean age: 62 ± 8 years) were subjected to axial impact loads using a custom-built pneumatic impactor, with one specimen from each pair tested at velocity and impact durations representative of a military blast condition, and the contralateral under conditions representing an automotive collision. Impacts were applied in increasing levels of intensity (defined using energy levels) until fracture occurred. Fracture risk was influenced by projectile velocity, kinetic energy, impulse, and load rate, and there was a significant difference in peak force (p = 0.023), impulse (p = 0.09), and load rate (p = 0.025) between the automotive and military test conditions causing fracture. A 10% risk of fracture corresponded to an impact force of 9.0kN for the automotive condition and 12.2kN for the military condition. These results suggest that fracture tolerances developed in studies that simulate automotive impacts cannot be directly applied to military impacts of shorter duration. The number of factors identified to predict injury also suggests that fracture is not controlled by a single variable.

The purpose of this work was to develop and validate a finite element model of the distal radius to simulate impact loading. Eight-node hexahedral meshes of the bone and impactor components were created. Three separate impact events were simulated by altering the impact velocity assigned to the model projectile (pre-fracture, crack and fracture). Impact forces and maximum and minimum principal strains were calculated and used in the validation process by comparing with previously collected experimental data. Three measures of mesh quality (Jacobians, aspect ratios and orthogonality) and four validation methods (validation metric, error assessment, fracture comparisons and ensemble averages) assessed the model. The element Jacobians, aspect ratios and orthogonality measures ranged from 0.08 to 12, 1.1 to 26 and −70° to 80°, respectively. The force and strain validation metric ranged from 0.10 to 0.54 and 0.35 to 0.67, respectively. The estimated peak axial force was found to be a maximum of 28.5% greater than the experimental (crack) force, and all forces fell within ±2 standard deviation of the mean experimental fracture forces. The predicted strains were found to differ by a mean of 33% across all impact events, and the model was found to accurately predict the location and severity of bone damage. Overall, the model presented here is a valid representation of the distal radius subjected to impact.

Human bones are vulnerable to injury from a wide range of events, such as falls, automotive crashes, and sporting collisions, to name a few. In order to evaluate protective measures, the injury limits of whole bones need to be established through impact testing, which is typically done on cadavers. This allows investigation of the factors that influence injury, and using statistical methods, safety limits can be established, which are used by industry to assess risk during various events. Furthermore, the injury tolerance of whole bones must be identified and translated to measures obtained using surrogates, such as anthropomorphic test devices (ATDs, or “crash test dummies”), in order to be used outside of the research lab environment. Lastly, an understanding of the factors that influence fracture allows development of better protective measures, thus reducing the incidence and severity of these debilitating injuries. Therefore, this chapter explains high-speed impact testing of whole bone, as well as how to analyze, present, and interpret results.

During a frontal collision, there are a range of lower extremity postures that the vehicle's occupant may assume, potentially changing the way load is transmitted to this region of the body. While most experimental studies on the tibia's injury tolerance assume that load is directed along the leg's long axis, the effects of off-axis loading due to non-standard postures have not been well quantified, and commonly-cited injury criteria such as the Tibia Index do not directly account for posture. Therefore, twelve cadaveric tibias (paired from six donors) were subjected to off-axis impact loading in a custom-built test apparatus. One specimen from each pair was held at an angle of 15° relative to the direction of loading, while the contralateral was held at an angle of 30°, with these angles representing ankle plantarflexion and corresponding knee extension in a vehicle occupant. Specimens held at 30° fractured at lower forces than the specimens held at 15° (mean force = 5.8 vs. 7.5 kN). This indicates that posture should be incorporated into injury criteria for the tibia in future safety assessments instead of using a single force value based on axial impacts.

The foot/ankle complex is frequently injured in many types of debilitating events, such as car crashes. Numerical models used to assess injury risk are typically minimally validated and do not account for ankle posture variations that frequently occur during these events. The purpose of this study was to evaluate a finite element model of the foot and ankle accounting for these positional changes. A model was constructed from computed tomography scans of a male cadaveric lower leg and was evaluated by comparing simulated bone positions and strain responses to experimental results at five postures in which fractures are commonly reported. The bone positions showed agreement typically within 6° or less in all anatomical directions, and strain matching was consistent with the range of errors observed in similar studies (typically within 50% of the average strains). Fracture thresholds and locations in each posture were also estimated to be similar to those reported in the literature (ranging from 6.3 kN in the neutral posture to 3.9 kN in combined eversion and external rotation). The least vulnerable posture was neutral, and all other postures had lower fracture thresholds, indicating that examination of the fracture threshold of the lower limb in the neutral posture alone may be an underestimation. This work presents an important step forward in the modeling of lower limb injury risk in altered ankle postures. Potential clinical applications of the model include the development of postural guidelines to minimize injury, as well as the evaluation of new protective systems.

The foot–ankle complex is frequently injured in a wide array of debilitating events such as car crashes. Numerical models and experimental tests have been used to assess injury risk, but most do not account for the variations in ankle posture that frequently occur during these events. In this study, the positions of the bones of the foot–ankle complex (particularly, the hindfoot) were quantified over a range of postures. Computed tomography scans were taken of a male cadaveric leg under axial loading with the ankle in five postures in which fractures are commonly reported. The difference in the location of the talus and calcaneus between the neutral and each repositioned posture was quantified, and substantial rotations and displacements were observed for all postures tested (talus: 3°–21.5°, 1.5–10.5 mm; calcaneus: 10°–20°, 1.5–24.5 mm). Strains were also recorded at six locations on bones of the ankle during testing and were found to be highest in the calcaneus during inversion-external rotation and highest in the talus during eversion-external rotation. Postural changes likely affect the load pathway of the foot–ankle complex, potentially altering the stress and strain fields from that of the neutral case and changing the location of fracture. This highlights the need for injury-predicting studies examining the effect of these positional changes and to develop revised injury criteria accounting for the most vulnerable conditions.

Lower leg injury risk is commonly assessed using an anthropomorphic test device (ATD). The current standard leg (the HIII) has been shown to have low biofidelity due to its geometry and material properties. A new surrogate (the MIL-Lx) was developed to address these issues, specifically for anti-vehicular mine blast scenarios but with potential applications to high-force crashes in the automotive industry. Before it is adopted for use, the MIL-Lx must be evaluated under impact loading to ensure that it represents the natural lower leg response.Axial impact loads were applied to both the HIII and the MIL-Lx at impact velocities of 2 to 7 m/s using a pneumatic impacting device. Testing was also conducted with the foot removed from both surrogates to enable comparison with previous tests of isolated cadaveric tibias at noninjurious and injurious (i.e., fracture) levels. To evaluate the effect of a boot on load attenuation, the HIII was impacted with and without a hiking boot.Forces in the MIL-Lx were between 25 and 100 percent of those in the HIII (depending on impact conditions). The use of a boot reduced the peak force by approximately 65 percent at the highest impact velocities. The MIL-Lx fit the data from noninjurious cadaveric tibia tests with R(2) = 0.83.The MIL-Lx is a new surrogate that represents the response of the natural tibia under axial impact loading better than the HIII. The inclusion of a boot has a significant effect on loads in the leg and may influence injury assessment results. The MIL-Lx will be a useful tool for predicting lower leg injury risk over a wide range of impact velocities.

Purpose Anterior flanges have been added to the humeral components of some total elbow arthroplasty systems to improve load transfer to the humerus and thereby reduce stress shielding in an effort to decrease the incidence of loosening. Either a wedge of bone or bone cement is placed between the anterior surface of the humerus and the flange. The purpose of this study was to quantify the cortical strains in the humerus as a function of these implantation options. Methods Five cadaveric distal humeri were fitted with bending strain gauges at 2 levels on the diaphysis and axial strain gauges at 1 level. Each specimen was subjected to cantilevered bending and axial compressive loads. Subsequently, a humeral prosthesis was inserted, and testing was repeated with 3 materials behind the flange: no graft (simulating an implant with no flange), a wafer of cancellous bone, and a block of bone cement. Results The presence of an anterior flange had no significant effect on load transfer through the distal humerus regardless of graft material. This was found to be consistent for both bending and axial loading modes at all gauge levels; however, the supporting collar effect of the implant may have influenced axial compression results. Conclusions These results suggest that for the Latitude humeral component studied, the placement of bone or bone cement behind the anterior flange may not influence the cortical strains in the distal humerus under bending loads. However, a flange may still influence cortical strains using another implant with different geometric and material properties than the currently studied design.

Finite element models apply material properties using experimentally derived density–modulus equations and computed tomographic image data, yet numerous different equations exist in the literature. The purpose of this study was to experimentally evaluate the distribution of mechanical properties through the proximal tibia and compare with those predicted using existing density–modulus equations. Indentation testing was performed on five cadaveric tibiae, with four slices removed from the proximal epiphysis and metaphysis of each. Elastic modulus and yield strength were identified for each test and grouped into nine transverse regions. These regions were identified on computed tomographic scans, and four density–modulus equations from the literature applied. Errors between measured and predicted modulus were then calculated. Elastic modulus and yield strength varied regionally, with the bone located closest to the joint and in the condyles being strongest and the intercondylar region the weakest. The optimal relationship for predicting modulus varied depending on anatomical region, but generally was best predicted by the Goulet equation. The regions of high strength identified in this study (condyles and proximal regions) can serve as improved sites of attachment for orthopedic devices and should be preserved during surgery, if possible. The substantial regional variations observed herein (almost a threefold change in modulus across different regions) should be incorporated into finite element models and applied using the Goulet density–modulus equation.

Background Current stabilization methods for periprosthetic fractures of the distal femur are inadequate in achieving fracture fixation, with complication rates as high as 29%. A major contributor to poor outcomes is that these methods rely only on screw purchase in the bone to maintain fracture reduction. We designed, manufactured and evaluated a novel plating method that utilizes the femoral prosthesis to enhance stability for treatment of distal femoral periprosthetic fractures. Methods Medial and lateral plates were designed and manufactured based on geometry of a synthetic femur and femoral prosthesis. The two plates were linked via a compression screw and a small tab on each plate that inserted into pre-existing slots on the prosthesis. Mechanical tests (500 N compression or 250 N anterior directed cantilever bending), were performed on synthetic femurs with simple transverse fractures (3 mm gap) just superior to the distal femoral prosthesis that were stabilized using either the prototype plates or a single lateral plate. Translational movements of the fracture site during loading were measured using 3D motion tracking. Findings With the single lateral plate, the distal fragment experienced a resultant displacement of 0.40 mm under cantilever bending and 0.61 mm under compression (13% and 20% respectively of fracture gap width). With the bilateral plates, fracture gap motion was significantly reduced to 0.13 mm under bending and compression (4.3% of the fracture gap). Interpretation Our results indicate that a bilateral plating method is capable of improving stabilization of periprosthetic fractures compared to the traditional lateral plating technique.

During an anti-vehicular landmine event, the lower legs are particularly vulnerable to injury. Energy-attenuating (EA) floor mats are appealing in their potential to protect against the high-rate loading associated with such events, while consuming minimal space within the vehicle. To examine the efficacy of these mats, five commercially-available EA products were subjected to loading in an impact testing machine against an Anthropomorphic Test Device (ATD) leg. Over a range of test velocities, the ability of the mats to reduce axial tibial force in the ATD leg was quantified. Several of the mats reduced the tibial force by approximately 75% at the highest impact speed tested; however, when the results were extrapolated to the level of previously reported floor velocities, the injury threshold would be exceeded for all materials. EA floor mats are able to dissipate much of the energy from a blast, but cannot mitigate all of the loading to the lower legs during a landmine blast event.

BACKGROUND:: Impulse loading of the lower leg during events such as ejection seat landings or in-vehicle land mine blasts may result in devastating injuries. These impacts achieve higher forces over shorter durations than car crashes, from which experimental results have formed the current basis for protective measures of an axial force limit of 5.4 kN, as registered by an anthropomorphic test device (ATD). The hypotheses of this study were that the injury tolerance of the isolated tibia to short-duration axial loading is higher than that previously reported and that secondary parameters such as momentum or kinetic energy are significant for fracture tolerance, in addition to force. METHODS:: Seven pairs of cadaveric tibias were impacted using a pneumatic testing apparatus, replicating short-duration axial impulse events. One specimen from each pair was impacted with a light mass and the contralateral impacted with a heavy mass, to investigate the effects of momentum and kinetic energy, as well as force, on injury. Impacts were applied incrementally until failure. RESULTS:: Force, kinetic energy, age, and height were shown to be significant factors in the probability of fracture. A 10% risk of injury corresponded to an impact force of 7.9 kN, with an average kinetic energy of 240 J. In comparison, this same impact level applied to an ATD would register a force of 16.2 kN because of the higher stiffness of the ATD. CONCLUSIONS:: These results suggest that the current injury standard may be too conservative for the tibia during high-speed impacts such as in-vehicle land mine blasts and that factors in addition to force should be taken into consideration. Language: en

Composite synthetic bones are a commercially available substitute for cadaveric specimens, and they have previously been validated to replicate natural bone under quasi-static, non-destructive testing. Synthetic tibias could be used to analyse injury risk to the lower leg during impact events, but their failure mode must be validated by way of comparative tests to human bone. Synthetic tibias were instrumented with strain gauges and subjected to axial impact loading. Two different projectile masses were used for the tests, and the effects of force, momentum, and energy on failure were compared with previous cadaveric data. The composite tibias failed at forces between 37—45 per cent of those from cadavers, and failed via cortical delamination in combination with fracture. A Weibull analysis generated a survivability curve based on axial force at failure, and was shown to be lower than previous cadaveric curves. Failure was dependent on both the momentum and energy applied. Strain distributions through the synthetic tibias were significantly different from those of cadavers. The convex distal articular surface of the synthetic bones may partially account for the lower fracture tolerance. As a result of the many differences in response, these synthetic tibias are not recommended for use in impact fracture studies.

Composite synthetic bones are widely used in orthopaedic research. They offer many advantages over post mortem human specimens, including low inter-specimen variability in both geometry and material properties, ready availability, and ease of handling, storage and disposal. Fourth generation models of Sawbones® (Pacific Research Laboratories, Inc., Vashon, WA, USA) are made using a short glass fiber reinforced epoxy resin injected around a core of rigid polyurethane foam. These composite bones have been previously validated to replicate natural bone response at a quasi-static rate [1].Copyright © 2010 by ASME

Axial loading of the lower leg during impact events can cause significant fractures of the tibia. The magnitude of lower leg axial loading that occurs during short-duration high-impulse events, such as antivehicular landmine blasts, can lead to life-altering injuries. These events achieve higher forces over shorter durations than car crashes, the current standard used for protective measures. In order to determine appropriate injury limits for the lower limb, a testing apparatus has been designed that can simulate these types of events for testing of anthropomorphic test device (ATD) lower legs as well as cadaveric specimens. Moreover, the design allows for the velocity at which the specimen is struck to be varied independently of the force applied, thus allowing independent investigation into the effect of momentum or energy on fracture strength. Test specimens are supported on a low-friction bearing system, and receive the controlled impulse from a projectile of variable mass that is accelerated using pneumatics. The apparatus includes velocity sensors, a six-degree-of-freedom load cell, and an accelerometer to completely quantify the loading event. The apparatus’ performance was validated against an ATD lower leg. It was able to create impulse events with forces from 0.5 kN to 17.0 kN, and projectile speeds of 2.3–13.9 m/s. Various momenta could be achieved at a constant force level by varying the mass of the projectile, with a maximum difference of 65%, whereas kinetic energy was inherently linked to the impact force. This apparatus will be useful in future studies for determining the appropriateness of currently used injury limits for the lower limb to high-impulse events, as well as for quantifying the relationship between cadaveric fracture response and ATD measurements. This device can also be readily applied to other bones of the body, to create realistic fracture patterns for known injury mechanisms.

Purpose Implant design parameters can greatly affect load transfer from the implant stem to the bone. We have investigated the effect of length or material of distal ulnar implant stems on the surrounding bone strains. Methods Eight cadaveric ulnas were instrumented with 12 strain gauges and secured in a customized jig. Strain data were collected while loads (5–30 N) were applied to the medial surface of the native ulnar head. The native ulnar head was removed, and a stainless steel implant with an 8-cm–long finely threaded stem was cemented into the canal. After the cement had cured, the 8-cm stem was removed, leaving a threaded cement mantle in the canal that could accept shorter threaded stems of interest. The loading protocol was then repeated for stainless steel stems that were 7, 5, and 3 cm in length, as well as for a 5-cm–long titanium alloy (TiAl 6 V 4 ) stem. Other stainless steel stem lengths between 3 and 7 cm were tested at intervals of 0.5 cm, with only a 20 N load applied. Results No stem length tested matched the native strains at all gauge locations. No significant differences were found between any stem length and the native bone at the 5th and 6th strain gauge positions. Strains were consistently closer to the native bone strains with the titanium stem than the stainless steel stem for each gauge pair that was positioned on the bone overlying the stem. The 3-cm stem results were closer to the native strains than the 7-cm stem for all loads at gauges locations that were on top of the stem. Conclusions The results from this study suggest that the optimal stem characteristics for distal ulnar implants from a load transfer point of view are possessed by shorter (approximately 3 to 4 cm) titanium stems.