Biomechanical aspects of craniofacial sutures

Abstract

“Sutures” are articulations connecting the bones of the head each other’s through a fibrous sutural ligament. Their anatomical analysis is fundamental for the understanding of craniofacial development, and their biomechanical behaviour is relevant because of osteogenesis potential associated to the distraction of the sutural ligament i.e., the sutural distraction osteogenesis. Furthermore, maxillary sutures play an essential role because of the relevance of therapies such as the rapid maxillary expansion for the correction of craniofacial anomalies of the upper jaw. Thus, in this PhD thesis, a review has been done to analyse the mechanical parameters characterising sutures, revealing that little information was known about the biomechanical behaviour of the sutural ligament under loading. Subsequently, a swine (Sus scrofa) model was utilised throughout the thesis to investigate the relationship between the anatomy of the sutures and their position in the skull, and mechanical properties were assessed during distraction. Sutures were surgically removed and analysed by micro-computed tomography to measure sutural width, interdigitation, and ossification. Samples were then subjected to mechanical testing in tension together with acoustic emission analysis to characterise the distraction process under load. This seminal anatomical comparison of most of the sutures in the craniofacial skeleton, revealed that morphological parameters are different in distinct areas of the skull. Furthermore, acoustic emissions showed a significant relationship with mechanical behaviour of the sutural ligament. Additionally, attention was focused on the midpalatal suture and suture samples were collected from the anterior, median, and posterior regions of the palate. Histological, radiological, and biomechanical characterisations were performed to assess variations of the sutural width, interdigitation, ossification, bone mineral density, flexural stress, flexural strain and elastic modulus. A progressive increase in flexural stress and reduction in elasticity was exhibited along the rostro-caudal direction, and variations were related to interdigitation and ossification. Finally, the acoustic emission technique was applied during rapid maxillary expansion to evaluate the reaction of the craniofacial skeleton to the splitting of the midpalatal suture. Interestingly, although in the swine model the soft tissues create possible attenuation of the signal, acoustic emissions could be detected during rapid maxillary expansion with sensors positioned on the skin. Ultimately, these studies showed peculiar mechanical properties and anatomy of most of the sutures of the skull, stressing the importance of the application of specific criteria during the distraction osteogenesis of each suture. With regards to the midpalatal suture, the present findings also characterised its growth pattern, showing progressive ossification and reduced elasticity toward the caudal region, and applied novel techniques to analyse its reaction during rapid maxillary expansion.