Automatic anthropometric personalization of a digital human model from a set of subject's photographs.

The objective of the work is to develop a method for automatic dimensioning of a digital human model (DHM) from a set of calibrated photographs of the subject under study. Fifteen subjects (10 males, 5 females, mean age 27) wearing surface retro-reflective markers at major bony landmarks and standing inside a calibrated space, were photographed by means of low cost main stream digital cameras (face, left and right views). The DHM software used is based on a skeletal structure surrounded by contours defined by cross sections along the skeletal links. Specific points corresponding to bony landmarks are defined in body linkage local reference frames. The photograph calibration method (DLT) allows to superimpose a picture of the DHM on the subject's photographs. A specific algorithm adjusts the length of the manikin skeletal links in function of the measured distance between markers attached to these links (e.g. knee and ankle for the lower leg). Then the contour sections dimensions were adjusted to fit subject's silhouette extracted from the photographs. The results obtained within a few seconds of calculation consist of a personalized DHM representing the subject with an error less than 2% for stature and less than 4% for weight.

Clavicle fracture prediction: simulation of shoulder lateral impacts with geometrically personalized finite elements models.

BACKGROUND: Human body numerical models can help to develop protection devices against effects of road crashes. In the context of a side impact, a shoulder model able to predict shoulder injuries and more especially clavicle fracture would be helpful. METHODS: A shoulder model derived from an existing finite element model of the human body representing an average male (50th percentile), HUMOS1, has been upgraded. An isolated clavicle model was assessed thanks to experimental corridors derived from dynamic tests up to failure. Then, the whole upgraded shoulder model was evaluated by comparison with results from experimental side impact tests on the shoulder. Eventually, the upgraded model was geometrically personalized toward the anthropometry of the subjects and its ability to simulate fractures was assessed. RESULTS: The isolated clavicle model was assessed as validated. The upgraded 50th percentile shoulder model provided accurate results in the subinjurious domain. At higher velocities, the personalized models produced realistic shoulder injuries: clavicle fracture was accurately predicted in four cases of six, the model was conservative for the two other cases. CONCLUSION: The upgraded shoulder model presented here was successfully submitted to a rigorous assessment process. Once geometrically personalized, it provided positive results for clavicle fracture prediction. As clavicle fracture is the major shoulder injury, this model could help the design of safety devices for shoulder protection. Furthermore, this study enhances the need for geometrical personalization methods when using finite element model for injury risk prediction.

3D deformation and dynamics of the human cadaver abdomen under seatbelt loading.

According to accident analysis, submarining is responsible for most of the frontal car crash AIS 3+ abdominal injuries sustained by restrained occupants. Submarining is characterized by an initial position of the lap belt on the iliac spine. During the crash, the pelvis slips under the lap belt which loads the abdomen. The order of magnitude of the abdominal deflection rate was reported by Uriot to be approximately 4 m/s. In addition, the use of active restraint devices such as pretensioners in recent cars lead to the need for the investigation of Out-Of-Position injuries. OOP is defined by an initial position of the lap belt on the abdomen instead of the pelvis resulting in a direct loading of the abdomen during pretensioning and the crash. In that case, the penetration speed of the belt into the abdomen was reported by Trosseille to be approximately 8 to 12 m/s. The aim of this study was to characterize the response of the human abdomen in submarining and OOP. A total of 8 PMHS abdomens were loaded using a lap belt. In order to investigate the injury mechanisms, the abdominal deflection rate and the compression were imposed such that they were not correlated. The specimens were seated upright in a fixed back configuration. The lap belt was placed at the level of the mid-umbilicus, between the iliac crest and the 12th rib. The belt was pulled horizontally along the sides of the specimens causing a symmetrical loading of the abdomen. In addition to the local parameters such as the belt and back forces or the belt displacements, the 3D external deformation of the abdomen was recorded. The forces measured between the back of the cadaver and the seat showed that a mass effect should be taken into account in the abdominal behaviour in addition to viscosity. The back force was greater than the belt force in low speed (submarining like) tests while it was lower for high-speed (OOP like) tests. A lumped parameter model was developed to confirm the experimental results and to be able to compare the load penetration characteristics to the results reported in the literature. The injury outcomes are provided and compared to all the published data. The PMHS sustained MAIS2-3 abdominal injuries in the low speed tests and MAIS2-4 injuries in the high speed tests. Finally, the dynamic 3D deformation of the abdominal wall was reconstructed and is provided for further validation of finite element models of the human abdomen.

Influence of geometrical personalization on the simulation of clavicle fractures.

Finite element body models enable the evaluation of car occupant protection. In general, these models represent average males and inter-individual geometry variability is not taken into account. As the most frequent shoulder injury during car lateral accidents is a clavicle fracture, the purpose of this study is to investigate whether clavicle geometry has an influence on bone response until failure, and whether geometrical personalization of clavicle models is required. Eighteen clavicles from 9 subjects (5 males and 4 females, mean age: 76 +/- 12 years) were harvested. Six clavicles were scanned, enabling the development of subject-specific models and the quantification of geometrical features defining shape and cortical thickness. Bone mineral densities (BMD) were measured through double X-ray absorptiometry. Then, the general clavicle responses to dynamic compression until failure were studied. Simulations of the compression tests were carried out with the subject-specific models to assess the sensitivity of force-deflection clavicle responses to geometrical features. Clavicle fractures occurred at an average velocity of 1.41 +/- 0.4 ms(-1), with a fracture force of 1.48 +/- 0.46 kN and a deflection of 5.4 +/- 1.1 mm. A significant difference was found between male and female clavicle force values at rupture although their BMDs were not significantly different. Simulations with subject-specific models led to the conclusion that cortical bone thickness and bone shape have large effects on bone responses until failure and on fracture location. This study highlights the need for a geometrical personalization of clavicle models in order to take into account both gender discrepancies concerning clavicle shape and aging effects affecting cortical thickness.

Proportion of skin surface area of children and young adults from 2 to 18 years old.

When studying the density of skin lesions, calculations of relative density are based on charts of proportion of skin surface area. However, the current source of information is derived from skewed data obtained at the beginning of the twentieth century. Using more recent data from a population-based sample of children in the United States, we propose a new set of tables. Data from measurements taken in the United States in the 1970s for design and safety were applied to the computer-based model MAN3D. This model, originally created for ergonomic studies in the automotive industry, allowed us to obtain a precise estimate of the main surface areas of children. Compared with previously published studies, our estimates increased the relative proportion of arms and of the trunk and allowed for differentiation of these proportions by sex. New tables are proposed for epidemiological studies of skin lesion density in children.

Finite element modeling of the head skeleton with a new local quantitative assessment approach.

The present study was undertaken to build a finite element model of the head skeleton and to perform a new assessment approach in order to validate it. The application fields for such an improved model are injury risk prediction as well as surgical planning. The geometrical reconstruction was performed using computed tomography scans and a total of 4680 shell elements were meshed on the median surface of the head skeleton with the particular characteristic of adapted mesh density and real element thickness. The assessment protocol of the finite element model was achieved using a quasi-static experimental compression test performed on the zygomatic bone area of a defleshed isolated head. Mechanical behavior of the finite element model was compared to the real one and the assessment approach was divided into two steps. First, the mechanical properties of the anatomical structure were identified using the simulation and then the simulated displacement field was compared to local displacement measurement performed during test using a digital correlation method. The assessment showed that the head skeleton model behaved qualitatively like the real structure. Quantitatively, the local relative error varied from 8% up to 70%.

Comparison of Hybrid III, Thor-alpha and PMHS Response in Frontal Sled Tests.

Two series of nine frontal sled tests were conducted to evaluate the behavior of the Hybrid III and Thor-alpha dummies. The first series was conducted at 50 kph with airbag and 4 kN force-limited shoulder belt and the second series at 30 kph and only a 4 kN force-limited shoulder belt. In each series, three replicate tests were conducted with each dummy and compared with three PMHS. The data provided by the same instrumentation located at the same position were compared to assess the biofidelity of both dummies. The results were mass scaled in order to account for the differences between the anthropometry of the cadaver. The good test-to-test repeatability for each dummy permitted to compare the mean value of each recorded parameter. Based on the cadaver response, the results show that the Thor-alpha provides responses that are more similar to those of PMHS than the Hybrid III. The flexible joints in the thoracic spine, the sternum design and the more humanlike ribcage give more similar accelerations than the Hybrid III as compared to those of the PMHS. Nevertheless, some parts have to be improved in order to better follow the behavior of the human subject. The head-neck complex, the chest, the shoulder and the pelvis of the Thor-alpha have a more humanlike behavior but some differences remain. The distribution of the deceleration between the components is sometimes different compared to those of the cadaver, even if the resultants are similar. The dummies and most particularly the Hybrid III are less sensitive to the change in restraint systems and tests conditions than a cadaver.