Simple anisotropic model of Bone Adaptation - SAMBA.

Bone presents the ability to adapt itself to the evolving mechanical environment. A simple anisotropic model for bone adaptation allowing reproducing the evolution of the elastic properties and the reorientation of the anisotropy frame is proposed is this work. The elastic properties are related to the value of the bone apparent density. The evolution law of the density is described via two functions reflecting the activities of the osteoclast and osteoblast cells. The anisotropy of the elastic properties of the bone is assumed evolving continuously between those of trabecular and compact tissues. The existence of a target material frame is assumed to describe its reorientation. The rate of rotation or spin of the material frame is supposed to be proportional to the target orientation angle and to the activity of the osteoclasts and osteoblasts. The mechanical stimulus governing the evolution of the apparent density is defined as the ratio between the current strain energy density and its critical value corresponding to the initiation of bone damage. The simulations showed that this simple model can reproduce some essential phenomena observed during bone adaptation process.

Case study: Lesions due to forced ritual scarification in Cameroon - A warning from cultural anthropology to forensic medicine.

Asylum seekers and refugees are constantly increasing worldwide because of human rights' violations and political-related abuses. As a result, some of them show scars due to torture and other forms of maltreatments. In addition, they may also present scars due to ethnical practices, namely ritual scarifications. This case study presents a victim who did not give consent to perform such ethnical practices on her body. The authors aim to enlighten the difficulty to understand the origin and the purpose of these specific injuries and the importance to know how to distinguish them from other forms of abuse. Indeed, it appears that such lesions follow a cultural path, meaning that the lesions are performed methodically and may show macroscopic differences compared to others. The story narrated by the victim can be helpful for the experts' assessment, regardless, they may present memory-loss issues. This represents the value of a correct injuries' diagnosis and the importance of cultural anthropology-related analyses. The cultural and social background are relevant since the injuries have their own signification because of their symbolism. Therefore, a multidisciplinary approach with a cultural anthropologist may have the possibility to help the forensic experts in understanding and interpreting such stories fostering their ability to better assess asylum seekers stories and their reliability.

An analytical modeling with experimental validation of bone temperature rise in drilling process.

Predicting the bone thermal response in a surgical operation remains a major challenge. In the previous works, metal machining theory has frequently been used to predict bone temperature in drilling process. However, several experimental studies demonstrate that the chip formation process is very complex compared to metal cutting. In the present study, a simplified analytical model based on the moving heat source approach combined with the method of image sources is developed. The heat source due to the drill-bit tip was supposed to be proportional to the cutting energy. The friction at the tool-hole contact was also considered. An experimental study was performed on fresh femur pig bone for cutting speeds from 2 to 20 m/min. Temperature rise, drilling forces and bone volume fraction were measured. The experimental validation showed that the model reproduces satisfactorily the increase in temperature up to the maximum value while it overestimates the temperature during the cooling stage. A parametric study (thermal boundary conditions, lateral friction) was also performed. From the predicted results, it appears that the model can be improved by considering the effects of the bone volume fraction which can present a significant variation in the bone sample.

Morphological validation of a novel bi-material 3D-printed model of temporal bone for middle ear surgery education.

BACKGROUND: A new model of 3D-printed temporal bone with an innovative distinction between soft and hard tissues is described and presented in the present study. An original method is reported to quantify the model's ability to reproduce the complex anatomy of this region. METHODS: A CT-scan of temporal bone was segmented and prepared to obtain 3D files adapted to multi-material printing technique. A final product was obtained with two different resins differentiating hard from soft tissues. The reliability of the anatomy was evaluated by comparing the original CT-scan and the pre-processed files sent to the printer in a first step, and by quantifying the printing technique in a second step. Firstly, we evaluated the segmentation and mesh correction steps by segmenting each anatomical region in the CT-scan by two different other operators without mesh corrections, and by computing distances between the obtained geometries and the pre-processed ones. Secondly, we evaluated the printing technique by comparing the printed geometry imaged using µCT with the pre-processed one. RESULTS: The evaluation of the segmentation and mesh correction steps revealed that the distance between both geometries was globally less that one millimeter for each anatomical region and close to zero for regions such as temporal bone, semicircular canals or facial nerve. The evaluation of the printing technique revealed mismatches of 0.045±0.424 mm for soft and -0.093±0.240 mm for hard tissues between the initial prepared geometry and the actual printed model. CONCLUSIONS: While other reported models for temporal bone are simpler and have only been validated subjectively, we objectively demonstrated in the present study that our novel artificial bi-material temporal bone is consistent with the anatomy and thus could be considered into ENT surgical education programs. The methodology used in this study is quantitative, inspired by engineer sciences, making it the first of its kind. The validity of the manufacturing process has also been verified and could, therefore, be extended to other specialties, emphasizing the importance of cross-disciplinary collaborations concerning new technologies.

In vivo study of human mandibular distraction osteogenesis. Part II: Determination of callus mechanical properties.

Distraction Osteogenesis (DO) is a surgical technique used to reconstruct bone defects. To improve the current treatment protocols, the knowledge of the mechanical properties of the bone regenerate is of major interest. The aim of this study, constituting the second part of our paper previously published in Acta of Bioengineering and Biomechanics, was to identify the elastic and viscous properties of bone callus. This is done in the case of a mandibular DO by analyzing the experimental measurements of the forces imposed on bone regenerate by a distraction device. The bone transport forces were evaluated thanks to strain gauges glued on the distraction device. A rheological model describing the callus constitutive behavior was developed and the material constants involved were identified. The time-dependent character of the bone regenerate mechanical behavior was confirmed. The viscous response of the mesenchymal tissue was described by two characteristic times. The first one describing the viscoelastic callus behavior was estimated to be 140 seconds and the second one representing the permanent bone callus lengthening was evaluated to be 5646 seconds. An average value of 0.35 MPa for the regenerate Young's modulus was deduced. The elastic properties of mesenchymal tissue found are in agreement with the rare data available in the literature.

In vivo study of human mandibular distraction osteogenesis. Part I: bone transport force determination.

Distraction Osteogenesis (DO) is a surgical technique used to reconstruct bone defects. The evolution of forces acting during DO is known to be strongly influencing the clinical issue of the treatment. The aim of this study was to determine experimentally the time-dependent forces imposed on bone regenerate by a distraction device in the case of a mandibular DO consecutive to a gunshot wound. To evaluate the bone transport forces, some fixing pins of the distraction device were equipped with strain gauges. Measurements were done during the first weeks of the treatment. An equilibrium analysis was achieved to determine the forces acting in bone regenerate from strains in the pins. Those quantities evolved during the records approximately from 5 N to 3-4 N and 2 N to 0-0.3 N for the tension and shear forces, respectively, depending on the record duration. For the longest record, the callus lengthening reached 0.17 mm during 75 minutes. This decrease of force and simultaneous callus extension can be attributed to the viscosity of regenerate and the elastic energy release of the device. Essential data were obtained concerning forces, extension and their evolution during mandibular DO. The low force level obtained was attributed to the absence of resistance of the soft tissues in the case of ballistic trauma restoration.