Biomechanical Characterization of Complex Thin Bone structures in The Human Craniofacial Skeleton

In spite of burgeoning of new technologies in the field of maxillofacial surgery, such as novel methods for osteosynthesis, bone substitution and bone regeneration, the reconstruction of the craniofacial skeleton (CFS) remains a challenge. Complications and failure in existing technologies and treatments for the CFS may be attributed in part to an incomplete understanding of the biomechanical environment in which these technologies are expected to perform. Characterizing the morphology and biomechanical behaviour of this complex and unique structure is important to understanding its global response to mechanical demands. This thesis aims to characterize the biomechanical behaviour of thin bone regions and sutures in the CFS. We investigated the impact of image degradation in CT scans on the ability to develop accurate specimen-specific FE models. Image degradation resulted in large increases in cortical thickness and decreases in scan intensity, which corresponded to significant changes in maximum principal strains in the FE models. A new semi-automated connectivity technique was developed to quantify the degree of fusion in sutures and revealed varying degrees of connectivity and interdigitation depending on the suture location. Morphological features characterized using this technique were incorporated into idealized suture FE models and analysed under multiple loading directions. The idealized FE models revealed that the impact of the number of interdigitations on the strain energy absorption in the suture/bone complex is dependent on the loading direction (inversely related under pressure and directly related under perpendicular and pressure loading); similar behaviour was seen in a μCT based specimen-specific FE model. Three-point bending tests on bone samples containing sutures revealed a positive correlation between the number of interdigitations and bending strength. Finally, experimental testing of full cadaveric heads demonstrated inter-specimen consistency in strain magnitude and direction under muscle loading in spite of morphological differences. Overall, these findings provide new insight into the complex morphology of the CFS, limitations of current clinical imaging and the biomechanical behaviour of thin bone structures and their articulations. This work forms a solid foundation for future development of image analysis, modeling and experimental investigations focused on characterizing the global behaviour of the CFS.Ph