Simulative investigation of the required level of geometrical individualization of the lumbar spines to predict fractures.

Injury mechanisms of the lumbar spine under dynamic loading are dependent on spine curvature and anatomical variation. Impact simulation with finite element (FE) models can assist the reconstruction and prediction of injuries. The objective of this study was to determine which level of individualization of a baseline FE lumbar spine model is necessary to replicate experimental responses and fracture locations in a dynamic experiment.Experimental X-rays from 26 dynamic drop tower tests were used to create three configurations of a lumbar spine model (T12 to L5): baseline, with aligned vertebrae (positioned), and with aligned and morphed vertebrae (morphed). Each model was simulated with the corresponding loading and boundary conditions from dynamic lumbar spine experiments. Force, moment, and kinematic responses were compared to the experimental data. Cosine similarity was computed to assess how well simulation responses match the experimental data. The pressure distribution within the vertebrae was used to compare fracture risk and fracture location between the different models.The positioned models replicated the injured spinal level and the fracture patterns quite well, though the morphed models provided slightly more accuracy. However, for impact reconstruction or injury prediction, the authors recommend pure positioning for whole-body models, as the gain in accuracy was relatively small, while the morphing modifications of the model require considerably higher efforts. These results improve the understanding of the application of human body models to investigate lumbar injury mechanisms with FE models.

Subject-Specific Geometry of FE Lumbar Spine Models for the Replication of Fracture Locations Using Dynamic Drop Tests.

For traumatic lumbar spine injuries, the mechanisms and influence of anthropometrical variation are not yet fully understood under dynamic loading. Our objective was to evaluate whether geometrically subject-specific explicit finite element (FE) lumbar spine models based on state-of-the-art clinical CT data combined with general material properties from the literature could replicate the experimental responses and the fracture locations via a dynamic drop tower-test setup. The experimental CT datasets from a dynamic drop tower-test setup were used to create anatomical details of four lumbar spine models (T12 to L5). The soft tissues from THUMS v4.1 were integrated by morphing. Each model was simulated with the corresponding loading and boundary conditions from the dynamic lumbar spine tests that produced differing injuries and injury locations. The simulations resulted in force, moment, and kinematic responses that effectively matched the experimental data. The pressure distribution within the models was used to compare the fracture occurrence and location. The spinal levels that sustained vertebral body fracture in the experiment showed higher simulation pressure values in the anterior elements than those in the levels that did not fracture in the reference experiments. Similarly, the spinal levels that sustained posterior element fracture in the experiments showed higher simulation pressure values in the vertebral posterior structures compared to those in the levels that did not sustain fracture. Our study showed that the incorporation of the spinal geometry and orientation could be used to replicate the fracture type and location under dynamic loading. Our results provided an understanding of the lumbar injury mechanisms and knowledge on the load thresholds that could be used for injury prediction with explicit FE lumbar spine models.

The Documentation of Injuries Caused by Traffic Accidents.

BACKGROUND: Persons injured in traffic accidents may have injuries of characteristic types that are of significance for the complex reconstruction of the accident and whose medicolegally sound clinical documentation is highly important. This is of particular relevance for the approximately 55 000 persons who are severely injured in traffic accidents in Germany each year. Gaps in documentation are often disadvantageous for the injured persons. METHODS: This review is based on pertinent publications retrieved by a selective literature review, with additional consideration of relevant textbooks in traffic medicine and legal medicine, as well as the guidelines of the AWMF (Association of the Scientific Medical Societies in Germany). RESULTS: Injuries in traffic accidents typically differ depending on the mode of participation of the injured person in traffic. They must be examined with a view toward the sequence of events of the accident and documented in medicolegally sound fashion. In particular, because of the different mechanical forces involved, it is important to document the seat that the injured person occupied in the automobile, the nature of the collision (pedestrian vs. automobile; bicycle, e-bike, e-scooter, and motorcycle accidents), and the protective devices that were in use. CONCLUSION: The precise documentation of injuries and examination findings, with critical consideration of their plausibility in relation to the sequence of events of the accident as far as it is known, is an important duty of the physician. This documentation serves as the basis for further judicial steps leading to compensation when legally appropriate.

Kinematic response of seated male volunteers in various reclined postures on a sled subjected to a braking pulse.

Vehicle occupants expect greater postural flexibility with the introduction of highly automated vehicles, such as reclined postures. Experiments have been conducted with post mortem human subjects to study the risk of injury under impact conditions in reclined postures. However, the influence of the pre-crash phase on the kinematics in reclined postures has not yet been thoroughly studied. The aim of the present study is to investigate human responses under low g braking conditions focusing on different backrest angles in a generic sled environment. Three 50th percentile male volunteers were recruited to participate in a sled experiment. Each of them was subjected to a total of fourteen trials under a braking pulse with a maximum acceleration of 0.7 g for 700 ms. Different sitting postures were investigated: from 23° to 45°, 60° and 75° backrest tilt with respect to the vertical axis. In addition, two different seat pan tilt angles were considered: a 16° tilt angle for 23°, 45° and 60° backrest inclination and a 36° tilt angle for 60° and 75° backrest inclination. Measurements of volunteer kinematics, muscle activation and interaction forces between the volunteers and the sled, among others, were acquired. Initial results show a significant reduction in maximum forward head displacement from the upright to the reclined postures (p < 0.02), with the exception of the 45° reclined posture. However, no significant difference in maximum head displacement was found between the different reclined postures (p > 0.1). Seat pan tilt angle did significantly influence forward head excursion when considering the same seatback inclination (p < 0.01). It is of great importance to investigate occupant kinematics during the pre-crash phase to understand its influence on the potential injuries that may occur with a reclined posture in the event of a collision.

Experimental characterisation of porcine subcutaneous adipose tissue under blunt impact up to irreversible deformation.

A deeper understanding of the mechanical characteristics of adipose tissue under large deformation is important for the analysis of blunt force trauma, as adipose tissue alters the stresses and strains that are transferred to subjacent tissues. Hence, results from drop tower tests of subcutaneous adipose tissue are presented (i) to characterise adipose tissue behaviour up to irreversible deformation, (ii) to relate this to the microstructural configuration, (iii) to quantify this deformation and (iv) to provide an analytical basis for computational modelling of adipose tissue under blunt impact. The drop tower experiments are performed exemplarily on porcine subcutaneous adipose tissue specimens for three different impact velocities and two impactor geometries. An approach based on photogrammetry is used to derive 3D representations of the deformation patterns directly after the impact. Median values for maximum impactor acceleration for tests with a flat cylindrical impactor geometry at impact velocities of 886 mm/s, 1253 mm/s and 2426 mm/s amount to 61.1 g, 121.6 g and 264.2 g, respectively, whereas thickness reduction of the specimens after impact amount to 16.7%, 30.5% and 39.3%, respectively. The according values for tests with a spherically shaped impactor at an impact velocity of 1253 mm/s are 184.2 g and 78.7%. Based on these results, it is hypothesised that, in the initial phase of a blunt impact, adipose tissue behaviour is mainly governed by the behaviour of the lipid inside the adipocytes, whereas for further loading, contribution of the extracellular collagen fibre network becomes more dominant.

Complementing femur model validation with a variability-focused approach.

OBJECTIVE: This short communication presents an approach as an objective means to validate that population variability is potentially incorporated into human body models in an accurate way, complementing existing validation techniques based on individual experiment-simulation comparison. This shall provide a further option for the assessment of the quality of large-number statistical simulations with human body models regarding their biofidelic behavior. METHODS: This population-based approach uses mathematical clustering methods to group similar curves of a combined population of numerical simulation results and experimental curves together. The resulting clusters can be used to assess the biofidelic behavior of numerical simulations, also with characteristics substantially differing from the experimental objects. This developed population-based approach was tested on a reference load case, the dynamic 3-point bending of the femur (Forman et al. 2012). RESULTS: The clustering approach rendered a distinction into 4 groups of response curves. For this small number, the grouping can be manually assessed as plausible. All experimental, and most numerical responses were grouped into one cluster. Three result curves constitute a cluster of their own, with their meta-data ranking on the margins of the population in at least one of the crucial biomechanical parameters. Such a result can be considered in accordance with the included experimental and anthropometric data. CONCLUSIONS: The feasibility of using such a cluster analysis without individual comparisons is demonstrated on a small set of results. It is used to judge whether a finite element model including aspects of the variation in a population is in agreement with experimental and anthropometric data. For experiments as the femur bending addressed here, it is of high importance to firstly ensure a gross match of curve shapes between experiments and simulation, i.e., capturing the relevant biomechanical aspects.

Potential effect of pre-activated muscles under a far-side lateral impact.

OBJECTIVE: The goal of this study is to evaluate the potential effect of muscle pre-activation under a lateral impact scenario, in this case focusing on a far-side impact, using an Active Human Body Model. METHODS: In total fourteen simulations were run, out of these, twelve were computed with an Active Human Body Model and two with a passive one. The models were subjected to a far-side impact scenario reaching up to 14 g's. Two different pre-crash scenarios were analyzed with the Active Human Body Model: (1) constant velocity, and (2) braking deceleration. During the pre-crash phase a lambda control based on the muscle length computed the muscle activation. Since there is no available data concerning the neuromuscular strategy of the occupants subjected to high accelerations, six different control strategies were analyzed during the in-crash phase. Besides, rib fracture and brain injury risk were analyzed, since they are the two most relevant body regions in this simplified far-side crash scenario. RESULTS: The pre-activation of the muscles showed an effect on both the occupant kinematics and estimated injury risks. Depending on the considered muscle strategy, the head lateral excursion varied up to 75 mm, specifically for the scenario with constant velocity. Moreover, the rib fracture probability and the brain injury indicator revealed higher injury risks for the passive Human Body Model. When applying the constant velocity during pre-crash, the fracture probability for two or more ribs ranged from 9.91 to 46.06% for the Active Human Body Model, whereas it reached 84.3% for the passive model. The brain injury indicator was reduced by about 10% when using the active model compared to the passive one. CONCLUSIONS: The numerical results show that the pre-activation of the muscles affects the kinematic and injury outcomes in car crashes. In this study, six muscular control strategies have been proposed. The two muscular controls that may be most realistic are: constant activation after the in-crash phase starts, by trying to hold the position prior to the crash, or no stimulation, by not responding to the upcoming in-crash event.

Subcutaneous adipose tissue thickness around the ASIS area for human body models in reclined positions.

OBJECTIVE: Subcutaneous adipose tissue (SAT) thickness above the anterior superior iliac spine (ASIS) influences belt fit of a vehicle occupant. To improve finite element (FE) human body models and their application assessing future seating positions in cars, there is a need for more detailed data. METHODS: Anthropometric input data were used to statistically model a lower limit of the SAT thickness in the area around the ASIS (at the ASIS or in the groin) extracted from 102 postmortem computed tomography (pmCT) data sets (56 males and 46 females). Additionally, 2 pmCT scans of 1 male individual in both supine and sitting conditions were used to estimate change in SAT thickness by position. RESULTS: Distributions and locations of minimum values for SAT thickness were derived for males and females. Sex, age, and body mass index (BMI) remained in a linear regression model for the minimum SAT thickness in the ASIS area. Thirty-seven percent of the variance in the SAT distribution of the sample can be explained by these input variables. The individual with data in supine and sitting positions showed an SAT thickness value above the ASIS 6 times higher in the sitting position than in the supine position. CONCLUSIONS: Individual factors influence SAT thickness around the ASIS in addition to BMI, sex, and age. The presented values need to be regarded as a lower limit of SAT thickness, because in 63% the minimum was found in the groin area and the measurements were performed in a supine position. The increase in SAT thickness in a sitting position compared to supine seen in the case example shows the need for further data acquisition to establish a transfer function interpolating between both positions. The SAT thickness minimum values in the ASIS area shown in this study can provide valuable input for soft tissue modeling in human body models with the aim to analyze seat belt fit and to computationally assess lap belt and occupant interaction sensitivity to SAT tissue thickness under load. This might be crucial in reclined sitting positions in automated driving.

Comparison of Upper Neck Loading in Young Adult and Elderly Volunteers During Low Speed Frontal Impacts.

Cervical pain and injuries are a major health problem globally. Existing neck injury criteria are based on experimental studies that included sled tests performed with volunteers, post-mortem human surrogates and animals. However, none of these studies have addressed the differences between young adults and elderly volunteers to date. Thus, this work analyzed the estimated axial and shear forces, and the bending moment at the craniocervical junction of nine young volunteers (18-30 years old) and four elderly volunteers (>65 years old) in a low-speed frontal deceleration. Since the calculation of these loads required the use of the mass and moment of inertia of the volunteers' heads, this study proposed new methods to estimate the inertial properties of the head of the volunteers based on external measurements that reduced the error of previously published methods. The estimated mean peak axial force (Fz) was -164.38 ± 35.04 N in the young group and -170.62 ± 49.82 N in the elderly group. The average maximum shear force (Fx) was -224.42 ± 54.39 N and -232.41 ± 19.23 N in the young and elderly group, respectively. Last, the estimated peak bending moment (My) was 13.63 ± 1.09 Nm in the young group and 14.81 ± 1.36 Nm in the elderly group. The neck loads experienced by the elderly group were within the highest values in the present study. Nevertheless, for the group of volunteers included in this study, no substantial differences with age were observed.

Multiscale Validation of Multiple Human Body Model Functional Spinal Units.

A validation comparing five human body model (HBM) lumbar spines is carried out across two load cases, with the objective to use and apply HBMs in high strain rate applications such as car occupant simulation. The first load case consists of an individual intervertebral disc (IVD) loaded in compression at a strain rate of 1/s by a material testing machine. The second load case is a lumbar functional spine unit (FSU) loaded in compression using a drop tower setup, producing strain rates of up to 48/s. The IVD simulations were found to have a better agreement with the experiments than the FSU simulations, and the ranking of which HBMs matched best to the experiment differed by load case. These observations suggest the need for more hierarchical validations of the lumbar spine for increasing the utility of HBMs in high strain rate loading scenarios.

Biological variability of cell-free DNA in healthy females at rest within a short time course.

INTRODUCTION: Alterations in cell-free DNA concentration (cfDNA) over time have been studied in diseased or injured patients or analyzed in athletes during exhaustive exercise. However, no fluctuations have been examined over a short time course in healthy humans at rest so far, wherefore the aim of this study was to examine individual variations at different time points within 75 min. METHODS: Serial blood drawing was performed in 14 healthy female volunteers at rest within 75 min. Plasma DNA was quantified by real-time qPCR, and absolute levels were analyzed together with relative variations. cfDNA alterations were moreover analyzed in consideration of potential volunteer-related impact factors (e.g., pulse) and were compared to alterations of plasma CK and AST. RESULTS: Absolute cfDNA concentration ranged from 0.6 to 3.4 ng/ml. Regarding alterations over time, positive and negative variations were identified, whereby the interdecile range of fold changes was from 0.5 to 1.4. The maximum fold change was determined at 10 min. No relations were found between cfDNA levels and the analyzed individual factors. CONCLUSION: We evidenced the variability of cfDNA in healthy humans at rest within a short time course. The determined variations should serve in future studies to distinguish small cfDNA increases after minor trauma from natural fluctuations. Without such reference of intra-individual variation at rest, it would not be feasible to distinguish an injury from a fluctuation with certainty. Thus, a basis was established for the application of cfDNA as biomarker for the detection of mild injuries in forensic biomechanics.

Maximum tensile stress and strain of skin of the domestic pig-differences concerning pigs from organic and non-organic farming.

The purpose of this work has been to determine differences in biomechanical properties of porcine skin from organic and non-organic farming as porcine skin is widely used as a model for human skin. A test apparatus was used, using gravity to stretch and finally tear a dumbbell-shaped specimen of prepared abdominal skin with a testing surface area of 25 × 4 mm. A total of 32 specimens were taken from seven individual pigs, three from organic and four from non-organic farming, in different orientations with respect to the Langer's lines. The tests were performed at a dynamic speed of around 1.66 m/s (corresponding to a nominal strain rate of 67 s-1). Engineering strain at rupture was higher in pig skin from non-organic farming with values up to 321% as opposed to 90% in organic pig skin. The maximum tensile stress found in non-organic pig skin was lower than in pig skin from organic farming with maximum values of 34 MPa as opposed to 58 MPa. The reason for the difference in biomechanical properties is unclear; the effect of sunlight is discussed as well as other factors like age and exercise. It seems that the biomechanical properties of porcine skin from organic farming are more similar to those of human skin.

Feasibility study of a safe sled environment for reclined frontal deceleration tests with human volunteers.

Objective: The goal of the study was to assess the feasibility of a safe crash environment for volunteer tests in reclined seating positions. An iterative multimodal approach was chosen, consisting of full-body human body model (HBM) simulations, anthropomorphic test device (ATD) physical testing, and volunteer testing.Methods: To estimate a noninjurious deceleration pulse, the iterative inclination of the seat was supported through HBM simulations and physical ATD testing. One male volunteer was exposed to 5 low-speed frontal sled impacts with stepwise reclined seat angles. The volunteer was restrained with a non-pretensioned 3-point seat belt. All procedures were approved by the relevant ethics boards.Results: Volunteer sled tests in 3 different seat configurations were performed with one volunteer at noninjurious deceleration levels. Inclination of the seat and the absence of a footrest resulted in elevated axial seat reaction forces and almost pure translational motion of the human body.Conclusions: A maximum speed of 7.1 km/h and peak deceleration of 3.0 g was found to be a safe pulse for volunteer testing in frontal impacts with a rigid reclined seat. Larger soft tissue deformations were observed when reclined, possibly associated with higher shear loads within the soft tissue. Preliminary results highlight trade-offs between the degree of seat angulation, friction force, and restraint capability of a 3-point seat belt, thus causing forward translation and/or axial spinal compression of the occupant that may need to be addressed in the future.

A priori prediction of the probability of survival in vehicle crashes using anthropomorphic test devices and human body models.

Objective: In the development of restraint systems, anthropomorphic test devices (ATDs) and human body models (HBMs) are used to estimate occupant injury risks. Due to conflicting objectives, this approach limits an injury severity risk tradeoff between the different body regions. Therefore, we present and validate a protocol for the aggregation of injury risks of body regions to a probability of survival (PoS). Methods: Injuries were clustered in regions similar to ATD or HBM investigations and the most severe injury as rated by the Maximum Abbreviated Injury Scale (MAIS) per body region was determined. Each injury was transformed into a dichotomous variable with regard to the injury severity level (e.g., MAIS 3+) whose injury risk was computed using the German In-Depth Accident Study (GIDAS) and NASS-CDS databases. Without loss of generality, we focus on 2 body regions-Head/face/neck (HFN) and chest (C)-at the MAIS 3+ level. The PoS was calculated using injury outcomes from the databases. The method of predicting PoS was validated by stratifying the database by crash type and technical crash severity. Results: The PoS of occupants injured in both HFN and C at the AIS 3+ level was found to be lower, at a statistically significant level, than that of occupants with AIS 3+ injuries to just one of the body regions. Focusing on occupants with only one body region injured at the AIS 3+ level, HFN injuries tended to decrease PoS more than chest injuries. For the validation cases, observed PoS could be reproduced in the majority of cases. When comparing predicted to observed values, a correlation of R2 = 0.92 was observed when not taking the restraint system into account. Focusing on frontal crashes, the correlation was R2 = 0.89. Considering only belted occupants, R2 increased to 0.93, whereas for cases with deployed airbag systems the R2 decreased to 0.68. The PoS for side crashes is reproduced with R2= 0.97 independent of the restraint system; it was 0.95 with belted occupants and 0.55 when also factoring in airbag deployment. Conclusions: The method showed an excellent predictive capability when disregarding the restraint system, or restraint-specific subgroups, for the considered validation cases.

Quantitative analysis of individual cell-free DNA concentration before and after penetrating trauma.

INTRODUCTION: Cell-free DNA (cfDNA) elevations were remarked in the blood of trauma patients. Published increases refer to comparative values of a healthy control group, ignoring thereby inter- and intra-individual differences under normal conditions. The aim of this study was to quantify cfDNA in patients in the time course of a planned orthopedic surgery, which constitutes the advantage of obtaining individual pre- and post-trauma values for each patient. By this approach, a basis should be established for the potential future application of cfDNA as biomarker for the detection of mild injuries related to volunteer experiments in forensic biomechanics. METHODS: Plasma samples of ten patients obtaining knee or hip arthroplasty were analyzed quantitatively for cfDNA by real-time qPCR the day prior operation (Prior), immediately afterwards (Day0), and the day after the surgery (Day1). RESULTS: Prior values exhibited a broad range, indicating pronounced inter-individual differences in the basic level of cfDNA. After surgery, levels were significantly elevated on both days (Wilcoxon test p = 0.002). In nine patients, highest values were measured on Day0, whereby a fold change of 19 was remarked once. After Day0, values decreased, though they did not reach Prior values until Day1 in nine patients. CONCLUSION: Endoprosthesis surgery represents a well-defined trauma scenario for the measurement of individual cfDNA elevations. The analysis of pre- to post-trauma alterations lay the groundwork for the application of cfDNA as biomarker for the detection of minor injuries in the field of forensic biomechanics.

Chest injuries of elderly postmortem human surrogates (PMHSs) under seat belt and airbag loading in frontal sled impacts: Comparison to matching THOR tests.

OBJECTIVE: The goal of the study was to develop experimental chest loading conditions that would cause up to Abbreviated Injury Scale (AIS) 2 chest injuries in elderly occupants in moderate-speed frontal crashes. The new set of experimental data was also intended to be used in the benchmark of existing thoracic injury criteria in lower-speed collision conditions. METHODS: Six male elderly (age >63) postmortem human subjects (PMHS) were exposed to a 35 km/h (nominal) frontal sled impact. The test fixture consisted of a rigid seat, rigid footrest, and cable seat back. Two restraint conditions (A and B) were compared. Occupants were restrained by a force-limited (2.5 kN [A] and 2 kN [B]) seat belt and a preinflated (16 kPa [A] and 11 kPa [B]; airbag). Condition B also incorporated increased seat friction. Matching sled tests were carried out with the THOR-M dummy. Infra-red telescoping rod for the assessment of chest compression (IRTRACC) readings were used to compute chest injury risk. PMHSs were exposed to a posttest injury assessment. Tests were carried out in 2 stages, using the outcome of the first one combined with a parametric study using the THUMS model to adjust the test conditions in the second. All procedures were approved by the relevant ethics board. RESULTS: Restraint condition A resulted in an unexpected high number of rib fractures (fx; 10, 14, 15 fx). Under condition B, the adjustment of the relative airbag/occupant position combined with a lower airbag pressure and lower seat belt load limit resulted in a reduced pelvic excursion (85 vs. 110 mm), increased torso pitch and a substantially lower number of rib fractures (1, 0, 4 fx) as intended. CONCLUSIONS: The predicted risk of rib fractures provided by the THOR dummy using the Cmax and PC Score injury criteria were lower than the actual injuries observed in the PMHS tests (especially in restraint condition A). However, the THOR dummy was capable of discriminating between the 2 restraint scenarios. Similar results were obtained in the parametric study with the THUMS model.

Fatal falls in the elderly and the presence of proximal femur fractures.

Fatal falls are frequent and seem to be an increasing problem in the elderly. Especially ground level falls (GLFs) and falls on or from stairs and steps (stairs falls) are worth examining for forensic classification and in order to improve the development of preventive measures. We retrospectively analyzed 261 fatal falls of elderly age 65 + years, which were autopsied at the Institute of Legal Medicine in Munich between 2008 and 2014. After careful screening, the sub-set of all 77 GLFs and 39 stairs falls were analyzed towards socio-demographic characteristics, fall circumstances, injuries, and circumstances of death. A subsequent analysis of GLF cases regarding the presence of proximal femur fractures (PFF) was performed. The injury pattern of the GLFs and the stairs falls clearly differ with a higher share of injuries to the lower extremities in the GLFs. However, the most severely injured body region was the head in both groups (62% of the stairs cases, 49% of the GLF cases). Alcohol as contributing to the fall was seen more frequently in the stairs falls. PFF were not seen in the stairs falls, but then in 18 GLF cases. Yet, for 17 among them (22% of 77), their hip fracture was the only serious injury leading to hospitalization and death. Only one GLF case was already found dead. This finding indicates a potential of avoiding up to 22% of the GLF fatalities by preventing hip fractures by optimized hip protectors or other measures, especially for the elderly aged 75 + years.

Development of a Patient-Specific Finite Element Model for Predicting Implant Failure in Pelvic Ring Fracture Fixation.

Introduction. The main purpose of this study is to develop an efficient technique for generating FE models of pelvic ring fractures that is capable of predicting possible failure regions of osteosynthesis with acceptable accuracy. Methods. Patient-specific FE models of two patients with osteoporotic pelvic fractures were generated. A validated FE model of an uninjured pelvis from our previous study was used as a master model. Then, fracture morphologies and implant positions defined by a trauma surgeon in the preoperative CT were manually introduced as 3D splines to the master model. Four loading cases were used as boundary conditions. Regions of high stresses in the models were compared with actual locations of implant breakages and loosening identified from follow-up X-rays. Results. Model predictions and the actual clinical outcomes matched well. For Patient A, zones of increased tension and maximum stress coincided well with the actual locations of implant loosening. For Patient B, the model predicted accurately the loosening of the implant in the anterior region. Conclusion. Since a significant reduction in time and labour was achieved in our mesh generation technique, it can be considered as a viable option to be implemented as a part of the clinical routine to aid presurgical planning and postsurgical management of pelvic ring fracture patients.

Corrigendum to "Development of a Patient-Specific Finite Element Model for Predicting Implant Failure in Pelvic Ring Fracture Fixation".

[This corrects the article DOI: 10.1155/2017/9403821.].

Development of a strain rate dependent material model of human cortical bone for computer-aided reconstruction of injury mechanisms.

Computer-aided methods such as finite-element simulation offer a great potential in the forensic reconstruction of injury mechanisms. Numerous studies have been performed on understanding and analysing the mechanical properties of bone and the mechanism of its fracture. Determination of the mechanical properties of bones is made on the same basis used for other structural materials. The mechanical behaviour of bones is affected by the mechanical properties of the bone material, the geometry, the loading direction and mode and of course the loading rate. Strain rate dependency of mechanical properties of cortical bone has been well demonstrated in literature studies, but as many of these were performed on animal bones and at non-physiological strain rates it is questionable how these will apply in the human situations. High strain-rates dominate in a lot of forensic applications in automotive crashes and assault scenarios. There is an overwhelming need to a model which can describe the complex behaviour of bone at lower strain rates as well as higher ones. Some attempts have been made to model the viscoelastic and viscoplastic properties of the bone at high strain rates using constitutive mathematical models with little demonstrated success. The main objective of the present study is to model the rate dependent behaviour of the bones based on experimental data. An isotropic material model of human cortical bone with strain rate dependency effects is implemented using the LS-DYNA material library. We employed a human finite element model called THUMS (Total Human Model for Safety), developed by Toyota R&D Labs and the Wayne State University, USA. The finite element model of the human femur is extracted from the THUMS model. Different methods have been employed to develop a strain rate dependent material model for the femur bone. Results of one the recent experimental studies on human femur have been employed to obtain the numerical model for cortical femur. A forensic application of the model is explained in which impacts to the arm have been reconstructed using the finite element model of THUMS. The advantage of the numerical method is that a wide range of impact conditions can be easily reconstructed. Impact velocity has been changed as a parameter to find the tolerance levels of injuries to the lower arm. The method can be further developed to study the assaults and the injury mechanism which can lead to severe traumatic injuries in forensic cases.