The role of soft tissues in cranial biomechanics - an investigation using advanced computer modelling techniques

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The skull forms a protective shell that encloses the brain and major sense organs. However, it is not an inert structure. During development, the interplay between cranial tissues helps to shape adult skull structure, and even in adult life there is an intimate dialogue between bone and cranial soft tissues that continues to modify and maintain cranial shape. Bone responds to strains, be they from feeding movements/jaw muscles, neck muscles, or the pressures exerted by blood vessels and other structures within the head. In recent years, the application of mechanical engineering software to biomechanics (by ourselves and others) has increased our understanding of the level and distribution of stresses experienced by the skull by everyday activities. However, it has become clear that the skulls of mammals and reptiles respond in different ways to similar stresses. Part of this difference may relate to skull shape - the enclosed shell-like skull of mammals versus the frame-like skull of many reptiles. However, none of these previous studies have taken into consideration a major component of cranial anatomy - the soft tissues that cover the skull on the one hand and are enclosed by it on the other. Together skull and soft tissues make up what some researchers have deemed a 'functional matrix'. Our objective is to examine the role of different parts of that matrix and determine whether they differ in mammal and reptile skulls.Our research group is interdisciplinary, with expertise in reptile and mammalian anatomy and evolution, biomechanical engineering, and the analysis of shape in relation to function. We have established a strong track-record and have pioneered an approach that combines the use of dynamic 3-D models (multibody dynamics analysis) and stress analysis (finite element analysis). This yields detailed, anatomically accurate working computer models of animal skulls, including joints (mobile and sutural) and muscles (jaw and neck). Through our previous funded research, we have built up a collection of detailed, anatomically correct, dynamic 3-D models of reptiles and mammals in which the skull, sutures, and both jaw and neck musculature are accurately rendered. These have been validated with in vivo analysis. These models will form the basis for the new project with the addition of accurately rendered soft tissue structures including periosteum, dura and cranial fascia; orbital contents; brain; and oral contents. The data for the anatomical work will be generated by dissection, contrast-stained CT scanning and MRI, and histological examination of fascial fibre types and arrangement.