Method for Evaluating Cortical Bone Young's Modulus: Numerical Twin Reconstruction, Finite Element Calculation, and Microstructure Analysis.

The determination of bone mechanical properties remains crucial, especially to feed up numerical models. An original methodology of inverse analysis has been developed to determine the longitudinal elastic modulus of femoral cortical bone. The method is based on a numerical twin of a specific three-point bending test. It has been designed to be reproducible on each test result. In addition, the biofidelity of the geometric acquisition method has been quantified. As the assessment is performed at the scale of a bone shaft segment, the Young's modulus values obtained (between 9518.29 MPa and 14181.15 MPa) are considered average values for the whole tissue, highlighting some intersubject variability. The material microstructure has also been studied through histological analysis, and bone-to-bone comparisons highlighted discrepancies in quadrants microstructures. Furthermore, significant intrasubject variability exists since differences between the bone's medial-lateral and anterior-posterior quadrants have been observed. Thus, the study of microstructures can largely explain the differences between the elastic modulus values obtained. However, a more in-depth study of bone mineral density would also be necessary and would provide some additional information. This study is currently being setup, alongside an investigation of the local variations of the elastic modulus.

Sudden death after facial impacts: Is the brainstem involved?

Three deaths following facial impacts in the presence of witnesses and resulting in brain lesions that were visualized only on pathological examination were studied at the forensic medicine institute of Marseille. Craniofacial impacts, even of low intensity, received during brawls may be associated with brain lesions ranging from a simple knock-out to fatal injuries. In criminal cases that are brought to court, even by autopsy it is still difficult to establish a direct link between the violence of the impact and the injuries that resulted in death. During a facial impact, the head undergoes a movement of violent forced hyperextension. Death may thus be secondary to the transmission of forces to the brain, either by a mechanism involving nerve conduction that may be termed a reflex mechanism (for example by vagal hyperstimulation) or by injury to the central nervous system (axonal damage). In such situations, autopsy does not make it possible to determine the cause of death, but only to suspect it in a context of voluntary violence in the presence of witnesses, with or without violent injury observed on external examination or on superficial incisions to determine the extent of bruises or hematoma. Systemic and comprehensive investigation involving pathology and toxicology is essential in any medicolegal case for positive interpretation and discrimination of other causes of death.

Characterization of the perinatal mandible growth pattern: preliminary results.

PURPOSE: The fetal development of the mandible is nowadays quite understood, and it is already known that craniofacial growth reaches its highest rate during the first 5 years of postnatal life. However, there are very few data focusing on the perinatal period. Thus, the present article is addressing this concern by studying the mandible morphology and its evolution around the birth with a morphometric method. METHODS: Thirty-one mandibles modelled in three dimensions from post-mortem CT-scans were analyzed. This sample was divided into two subgroups composed of, respectively, 15 fetuses (aged from 36 gestational weeks), and 16 infants (aged to 12 postnatal weeks). 17 distances, 3 angles, and 8 thicknesses were measured via the prior set of 14 landmarks, illustrating the whole mandible morphology. RESULTS: Although this methodology may depend on the image reconstruction quality, its reliability was demonstrated with low variability in the results. It highlighted two distinct growth patterns around birth: fetuses mandibles do not significantly evolve during the perinatal period, whereas, from the second postnatal weeks, most of the measurements increased in a homogeneous tendency and in correlation with age. CONCLUSIONS: The protocol developed in this study highlighted the morphologic evolution of the mandible around birth, identifying a different growth pattern from 2 postnatal weeks, probably because of the progressive activation of masticatory muscles and tongue. However, considering the small sample size, these results should be thorough, so identification and management of anatomic abnormalities could eventually be achieved.

Characterization of the very young child's palatal vault growth pattern: how do its size and shape evolve?

AIM: This study aimed to characterise the palatal vault evolution during the first years of life, both in terms of shape and size. MATERIALS: The study sample was composed of 168 healthy children aged less than 4 years. Twenty-one measurements of distances and 6 angles were taken from 7 fixed landmarks set on the palatal vaults 3D surfaces reconstructed from CT-scans. To analyse only the shape evolution, the "sizefree" log-shape ratio of those measurements were computed and the global shape of the palatal vault and their transversal curve were plotted. Statistical analyses were performed to highlight the shape and size differences separately. CONCLUSION: The shape and size evolution of the palatal vault during the first years of life was not only correlated with deciduous dentition development. We assumed that the progressive orofacial muscles activation and tongue movements in the oral cavity may also explain these results as they induced strains on the palatal vault, warping it in various ways.

Traction mechanical characterization of porcine mitral valve annulus.

The Mitral Annulus (MA) is an anisotropic, fibrous, flexible and dynamical structure. While MA dynamics are well documented, its passive mechanical properties remain poorly investigated to complete the design of adequate prostheses. Mechanical properties in traction on four sections of the MA (aortic, left, posterior and right segments) were assessed using a traction test system with a 30 N load cell and pulling jaws for sample fixation. Samples were submitted to a 1.5 N pre-load, 10 pre-conditioning cycles. Three strain rates were tested (5 %/min, 7 %/min and 13 %/min), the first two up to 10 % strain and the last until rupture. High-resolution diffusion-MRI provided microstructural mapping of fractional anisotropy and mean diffusion within muscle and collagen fibres. Ten MA from porcine hearts were excised resulting in 40 tested samples, out of which 28 were frozen prior to testing. Freezing samples significantly increased Young Moduli for all strain rates. No significant differences were found between Young Moduli at different strain rates (fresh samples 2.4 ± 1.1 MPa, 3.8 ± 2.2 MPa and 3.1 ± 1.8 MPa for increasing strain rates in fresh samples), while significant differences were found when comparing aortic with posterior and posterior with lateral (p < 0.012). Aortic segments deformed the most (24.1 ± 9.4 %) while lateral segments endured the highest stress (>0.3 MPa), corresponding to higher collagen fraction (0.46) and fractional anisotropy. Passive machinal properties differed between aortic and lateral segments of the MA. The process of freezing samples altered their mechanical properties. Underlying microstructural differences could be linked to changes in strain response.

Macrocrack propagation in a notched shaft segment of human long bone: Experimental results and mechanical aspects.

Experimenting with crack propagation in human cortical tissue is a necessary prerequisite for developing a cracking model. A three-point bending test on a shaft section of a notched human long bone is presented. A procedure for carrying out the experimental test, including unloading/reloading cycles, is implemented. The results obtained are analyzed regarding the physical mechanisms which occur in the different phases of the test, and during the cycles. The prominent role of cracking is highlighted. In addition a hypothesis is proposed concerning the potential effect of initial internal residual stresses, due to bone remodelling, on the significant residual notch openings after unloading and on the cycles' shape.

Modeling one-handed grip strangulation: Intentionality of the gesture and age influence.

Strangulation is a violent act which can be lethal and is often studied in forensic context. The neck includes several anatomical elements that can evolve with aging. We therefore created a numerical human neck model including the main anatomical elements and simulated one-handed grip strangulation cases. In addition, we created 3 models each representing age groups: 20-30 years old, 30-50 years old and over 50 years old. The main changes between the different age groups are the ossification of the cartilages and the muscles mechanical properties. Several initial and boundary conditions have been tested to perform a realistic simulation of one-handed grip strangulation. Stress analysis and fracture observation were compared with the grip strength of an average man, 552 N, to look at the intentionality of the gesture. In each age group, the results show no model fracture for a force of 552 N. It is necessary to reach a minimum of 1406 N before observing a first fracture on the hyoid bone. However, it is possible to get stresses on the hyoid bone and on the thyroid cartilage way before 552 N. It thus appears that the force created by one-handed grip strangulation is not sufficient to cause fractures of the bony elements of the neck, but it remains sufficient to compress the larynx and at least reduce airflow.

Preliminary results on the impact of simultaneous palatal expansion and mandibular advancement on the respiratory status recorded during sleep in OSAS children.

INTRODUCTION: The study aimed to evaluate the evolution of the respiratory status during sleep of OSAS children treated with a custom-made device combining maxillary expansion and mandibular advancement. MATERIAL AND METHODS: Sleep studies were performed before and after the treatment for 103 children presenting an initial OSAS and Class II malocclusion. Sleep questionnaires were also addressed to parents several years after the end of the treatment to evaluate its long-term effects. RESULTS: After nine months of treatment, the sleep breathing quality significantly improved: the Apnea/Hypopnea Index systematically decreased ≤5. According to the sleep questionnaires results, 84% of the patients did not show any loud or troubled breathing several years after the end of the treatment. DISCUSSION: Simultaneous maxillary expansion and mandibular advancement induced an increase of the oral space in the three spatial dimensions, helping in the significant improvement of the OSAS symptoms, with long-terms effects on the sleep breathing quality.

Finite element analysis of the human orbit. Behavior of titanium mesh for orbital floor reconstruction in case of trauma recurrence.

INTRODUCTION: The authors' main purpose was to simulate the behavior of a titanium mesh implant (TMI) used to reconstruct the orbital floor under the stress of a blunt trauma. MATERIALS AND METHODS: The orbital floor of a previously validated finite element model (FEM) of the human orbit was numerically fractured and reconstructed by a simplified TMI. Data from a CT scan of the head were computed with MICMICS (Materialise, Louvain, Belgium) software to re-create the skull's geometry. The meshing production, the model's properties management and the simulations of blunt traumas of the orbit were conducted on HYPERWORKS® software (Altair Engineering, Detroit, MI, USA). Some of the elements of the orbital floor were selected and removed to model the fracture; these elements were duplicated, their characteristics being changed by those of titanium to create a TMI covering this fracture. A 3D FEM composed of 640,000 elements was used to perform 21 blunt trauma simulations on the reconstructed orbit. RESULTS: In 90.4% (19/21) of the tests conducted, the TMI, whether free from any bony attachment or screwed to the orbital rim, has tended to move in the orbit and/or to deform. DISCUSSION: In the event of traumatic recurrence, which is not rare, TMIs may deform in a "blow-in" motion and threaten intra-orbital structures.

Development and validation of an optimized finite element model of the human orbit.

INTRODUCTION: The authors' main purpose was to develop a detailed finite element model (FEM) of the human orbit and to validate it by analyzing its behavior under the stress of blunt traumas. MATERIALS AND METHODS: A pre-existing 3D FEM of a human head was modified and used in this study. Modifications took into account preliminary research carried out on PubMed database. Data from a CT scan of the head were computed with Mimics® software to re-create the skull geometry. The mesh production, the model's properties and the simulations of blunt orbital traumas were conducted on Hyperworks® software. RESULTS: The resulting 3D FEM was composed of 640 000 elements and was used to perform blunt trauma simulations on an intact orbit. A total of 27 tests were simulated. Fifteen tests were realized with a metallic cylinder impactor; 12 tests simulated a hit by a closed fist. In all the tests conducted (27/27), the orbital floor was fractured. Fracture patterns were similar to those found in real clinical situations according to the buckling and hydraulic theories of orbital floor fractures. DISCUSSION: The similitude between the fracture patterns produced on the model and those observed in vivo allows for a validation of the model. This model constitutes, at the authors knowledge, the most sophisticated one ever developed.

Biomechanical study of the thyroid cartilage: A model of bi-digital strangulation.

The presence of fracture on neck elements is an indication of violence. Both the hyoid bone and the larynx can be damaged by a strangulation mechanism. Thyroid cartilage, more specifically, may present lesions in response to this mechanical stress. These lesions result in fractures at the bases of the horns of the thyroid cartilage. This study focuses on the thyroid cartilage behavior in cases of bi-digital strangulation, using an anthropometric and biomechanical approach. To develop a biomechanical model, we performed an anthropometric study taking into account 14 distances measurements as well as 3 measurements of angles. These measures allowed us to determine a significant sexual dimorphism between individuals. Then, we define 6 morphologies models, composed of 3 females and 3 males individuals. In order to visualize the ossification of the cartilage, each model has been tested with bone properties. Strangulation cases were simulated by applying an imposed velocity of 0.4m/s then 1m/s. We observed different behaviors of the thyroid cartilage according to the sex and the morphology.