Characterising and Modelling Calvarial Growth and Bone Formation in Wild Type and Craniosynostotic Type Mice

The newborn mammalian cranial vault consists of five flat bones that are joined together along their edges by soft tissues called sutures. The sutures give flexibility for birth, and accommodate the growth of the brain. They also act as shock absorber in childhood. Early fusion of the cranial sutures is a medical condition called craniosynostosis, and may affect only one suture (non-syndromic) or multiple sutures (syndromic). Correction of this condition is complex and usually involves multiple surgical interventions during infancy. The aim of this study was to characterise the skull growth in normal and craniosynostotic mice and to use this data to develop a validated computational model of skull growth. Two oncogenic series of normal and craniosynostosis (Crouzon) mice were microCT scanned and various morphological features of their skulls was characterised at postnatal days (P) 3, 7 and 10. Finite element model of a normal mouse at P3 was developed and used to predict the radial expansion of the skull and the pattern of bone formation at the sutures at P7 and P10. A series of sensitivity tests were carried out. Note the specific ages used in this study correspond to the age that this condition is diagnosed and treated in human. Results highlighted a good agreement between the finite element results and the ex vivo data both in terms of the radial expansion of the skull and the pattern of bone formation at the sutures. Nonetheless, the FE results were sensitive to the choice of input parameters. The modelling approach and the platform that was developed and validated here has huge potentials to be applied to human skull and to optimise the management of various forms of this condition

Application of Far Cortical Locking Technology in Periprosthetic Femoral Fracture Fixation: A Biomechanical Study

© 2016 Elsevier Inc. Background Lack of fracture movement could be a potential cause of periprosthetic femoral fracture (PFF) fixation failures. This study aimed to test whether the use of distal far cortical locking screws reduces the overall stiffness of PFF fixations and allows an increase in fracture movement compared to standard locking screws while retaining the overall strength of the PFF fixations. Methods Twelve laboratory models of Vancouver type B1 PFFs were developed. In all specimens, the proximal screw fixations were similar, whereas in 6 specimens, distal locking screws were used, and in the other six specimens, far cortical locking screws. The overall stiffness, fracture movement, and pattern of strain distribution on the plate were measured in stable and unstable fractures under anatomic 1-legged stance. Specimens with unstable fracture were loaded to failure. Results No statistical difference was found between the stiffness and fracture movement of the two groups in stable fractures. In the unstable fractures, the overall stiffness and fracture movement of the locking group was significantly higher and lower than the far cortical group, respectively. Maximum principal strain on the plate was consistently lower in the far cortical group, and there was no significant difference between the failure loads of the 2 groups. Conclusion The results indicate that far cortical locking screws can reduce the overall effective stiffness of the locking plates and increase the fracture movement while maintaining the overall strength of the PFF fixation construct. However, in unstable fractures, alternative fixation methods, for example, long stem revision might be a better option

Characterizing and Modeling Bone Formation during Mouse Calvarial Development

© 2019 American Physical Society. The newborn mammalian cranial vault consists of five flat bones that are joined together along their edges by soft fibrous tissues called sutures. Early fusion of these sutures leads to a medical condition known as craniosynostosis. The mechanobiology of normal and craniosynostotic skull growth is not well understood. In a series of previous studies, we characterized and modeled radial expansion of normal and craniosynostotic (Crouzon) mice. Here, we describe a new modeling algorithm to simulate bone formation at the sutures in normal and craniosynostotic mice. Our results demonstrate that our modeling approach is capable of predicting the observed ex vivo pattern of bone formation at the sutures in the aforementioned mice. The same approach can be used to model different calvarial reconstruction in children with craniosynostosis to assist in the management of this complex condition

Predicting calvarial growth in normal and craniosynostotic mice using a computational approach

© 2017 Anatomical Society During postnatal calvarial growth the brain grows gradually and the overlying bones and sutures accommodate that growth until the later juvenile stages. The whole process is coordinated through a complex series of biological, chemical and perhaps mechanical signals between various elements of the craniofacial system. The aim of this study was to investigate to what extent a computational model can accurately predict the calvarial growth in wild-type (WT) and mutant type (MT) Fgfr2 C342Y/+ mice displaying bicoronal suture fusion. A series of morphological studies were carried out to quantify the calvarial growth at P3, P10 and P20 in both mouse types. MicroCT images of a P3 specimen were used to develop a finite element model of skull growth to predict the calvarial shape of WT and MT mice at P10. Sensitivity tests were performed and the results compared with ex vivo P10 data. Although the mod els were sensitive to the choice of input parameters, they predicted the overall skull growth in the WT and MT mice. The models also captured the difference between the ex vivoWT and MT mice. This modelling approach has the potential to be translated to human skull growth and to enhance our understanding of the different reconstruction methods used to manage clinically the different forms of craniosynostosis, and in the long term possibly reduce the number of re-operations in children displaying this condition and thereby enhance their quality of life

Mechanical loading of cranial joints minimizes the craniofacial phenotype in Crouzon syndrome

Children with syndromic forms of craniosynostosis undergo a plethora of surgical interventions to resolve the clinical features caused by the premature fusion of cranial sutures. While surgical correction is reliable, the need for repeated rounds of invasive treatment puts a heavy burden on the child and their family. This study explores a non-surgical alternative using mechanical loading of the cranial joints to prevent or delay craniofacial phenotypes associated with Crouzon syndrome. We treated Crouzon syndrome mice before the onset of craniosynostosis by cyclical mechanical loading of cranial joints using a custom designed set-up. Cranial loading applied to the frontal bone partially restores normal skull morphology, significantly reducing the typical brachycephalic appearance. This is underpinned by the delayed closure of the coronal suture and of the intersphenoidal synchondrosis. This study provides a novel treatment alternative for syndromic craniosynostosis which has the potential to be an important step towards replacing, reducing or refining the surgical treatment of all craniosynostosis patients

Modelling human skull growth: a validated computational model

© 2017 The Author(s) Published by the Royal Society. All rights reserved. During the first year of life, the brain grows rapidly and the neurocranium increases to about 65% of its adult size. Our understanding of the relationship between the biomechanical forces, especially from the growing brain, the craniofacial soft tissue structures and the individual bone plates of the skull vault is still limited. This basic knowledge could help in the future planning of craniofacial surgical operations. The aim of this study was to develop a validated computational model of skull growth, based on the finite-element (FE) method, to help understand the biomechanics of skull growth. To do this, a two-step validation study was carried out. First, an in vitro physical three-dimensional printed model and an in silico FE model were created from the same micro-CT scan of an infant skull and loaded with forces from the growing brain from zero to two months of age. The results from the in vitro model validated the FE model before it was further developed to expand from 0 to 12 months of age. This second FE model was compared directly with in vivo clinical CT scans of infants without craniofacial conditions (n = 56). The various models were compared in terms of predicted skull width, length and circumference, while the overall shape was quantified using three-dimensional distance plots. Statistical analysis yielded no significant differences between the male skull models. All size measurements from the FE model versus the in vitro physical model were within 5%, with one exception showing a 7.6% difference. The FE model and in vivo data also correlated well, with the largest percentage difference in size being 8.3%. Overall, the FE model results matched well with both the in vitro and in vivo data. With further development and model refinement, this modelling method could be used to assist in preoperative planning of craniofacial surgery procedures and could help to reduce reoperation rates

Unravelling the structural variation of lizard osteoderms

Vertebrate skin is a remarkable organ that supports and protects the body. It consists of two layers, the epidermis and the underlying dermis. In some tetrapods, the dermis includes mineralised organs known as osteoderms (OD). Lizards, with over 7,000 species, show the greatest diversity in OD morphology and distribution, yet we barely understand what drives this diversity. This multiscale analysis of five species of lizards, whose lineages diverged ∼100–150 million years ago, compared the micro- and macrostructure, material properties, and bending rigidity of their ODs, and examined the underlying bones of the skull roof and jaw (including teeth when possible). Unsurprisingly, OD shape, taken alone, impacts bending rigidity, with the ODs of Corucia zebrata being most flexible and those of Timon lepidus being most rigid. Macroscopic variation is also reflected in microstructural diversity, with differences in tissue composition and arrangement. However, the properties of the core bony tissues, in both ODs and cranial bones, were found to be similar across taxa, although the hard, capping tissue on the ODs of Heloderma and Pseudopus had material properties similar to those of tooth enamel. The results offer evidence on the functional adaptations of cranial ODs, but questions remain regarding the factors driving their diversity

Evaluation of the stress pattern in the resin-based composite restoration of an endodontically treated premolar tooth: a finite element analysis study

This study aimed to assess the stress values in an endodontically treated maxillary premolar restored with a direct placement of adhesive composite restoration. An ortho-grade root-treatment was performed on a single-rooted maxillary premolar. Three types of cavities were prepared as follow: (1) O: Occlusal access cavity (one surface), (2): MO: access cavity with mesial extension equal to one third of bucco-palatal cusp width and 1 mm above the cementoenamel junction (two surfaces), (3) MOD: access cavity with mesial and distal extensions equal to one third of buccopalatal cusp width and 1 mm above the cementoenamel junction (three surfaces). After each restorative procedure, the restored-tooth complex was scanned using a micro-computed tomography scanner. A three-dimensional (3D) structure for each individual layer, including the enamel, dentine, composite restoration, and the gutta-percha of the restored tooth complex, was generated with interactive medical image processing software, whereas the biomechanical behavior and stress pattern distribution were evaluated using a finite element analysis software programme. The results revealed that the MO-restored tooth complex showed lower stress values than the onesurface (O) and three-surface (MOD) restored cavities. The generated stress values in the twosurface (MO) restored cavity in the present study were less than that of the one-surface (O) or three-surface (MOD) restored cavities. It can be concluded that, by increasing the C-factor, higher stress values are more likely to occur in the restored tooth. Greater stress values were observed in endodontically treated tooth with MOD restoration, which might have negative consequences on the fracture strength of the whole structure

Biomechanical behaviour of lizard osteoderms and skin under external loading

International audienceABSTRACT Many species of lizards are partially enveloped by a dermal armour made of ossified units called osteoderms. Lizard osteoderms demonstrate considerable species-specific variation in morphology and histology. Although a physical/protective role (against predators, prey, conspecifics and impact loading during falls) is frequently advanced, empirical data on the biomechanics of lizard osteoderms are scarce, limiting our understanding of form–function relationships. Here, we report deformation recorded at the surface of temporal osteoderms during controlled external loading of preserved specimens of 11 lizard species (Tiliqua rugosa, Tiliqua scincoides, Corucia zebrata, Pseudopus apodus, Timon lepidus, Matobosaurus validus, Broadleysaurus major, Tribolonotus gracilis, Tribolonotus novaeguineae, Heloderma horridum and Heloderma suspectum). Based on the strain recorded in situ and from isolated osteoderms, the skin of the species investigated can be ranked along a marked stiffness gradient that mostly reflects the features of the osteoderms. Some species such as T. rugosa and the two Heloderma species had very stiff osteoderms and skin while others such as T. lepidus and P. apodus were at the other end of the spectrum. Histological sections of the osteoderms suggest that fused (versus compound) osteoderms with a thick layer of capping tissue are found in species with a stiff skin. In most cases, loading neighbouring osteoderms induced a large strain in the instrumented osteoderm, attesting that, in most species, lizard osteoderms are tightly interconnected. These data empirically confirm that the morphological diversity observed in lizard osteoderms is matched by variability in biomechanical properties