Mechanisms of Craniofacial Fractures

4.1  Fractures of the Skull Base

Longitudinal and transversal struts of the skull base form a framework of strong bone pillars similar to that existing in the face. The longitudinal strut starts at the central origin of the lesser wing of the sphenoid bone and runs through the middle and posterior cranial fossa, forming the foramen magnum, and tapers into the occipital bone. The two axes of the transversal strut run anteriorly through the region of the lesser wing of the sphenoid bone and posteriorly through the region of the petrous part of the temporal bone, forming ridges, which strengthen the skull base.

Fractures of the skull almost exclusively develop through deformation of the skull along established weak points (Kretschmer 1978). Depending on the direction and force of the impact, burst or bending fractures occur. The anatomical classification differentiates between skull fractures as each of these groups presents distinct clinical findings, specific aspects of management, risks, and complications.

Burst fractures, for instance, are typical fractures of the anterior skull base and bear the risk of brain injuries through bone fragments impinging on the brain.

4.1.1  Burst Fractures

A broad impact on the skull may cause comminuted fractures directly at the impact site or the energy may be dispersed and lead to a compression of the skull and skull base, developing comminuted fractures indi rectly. The fine bone plates connecting the bony framework of the skull base are less elastic than the stronger bone struts. Thus, most skull base fractures

must be considered to be comminuted fractures. A transverse impact will result mostly in transverse fractures of the skull base, damaging the fifth and sixth cranial nerves where they emerge from the skull base. Longitudinal forces often result in comminuted fractures in the frontal base of the skull. Here, the optic and olfactory nerves are at risk to be damaged in the region of the optic canal and the roof of the ethmoidal cells (lamina cribrosa) (Probst 1971, 1986).

•Forces with a broad impact surface on the skull lead to compression, resulting in burst fractures of the skull base (Ernst et al. 2004)

4.1.2  Bending Fractures

Bending fractures occur preferably in the diploic bone architecture of the calvaria and are rarely seen in the skull base. A substantial force directed at a limited part of the skull bone can result in a typical impression fracture with the risk of brain damage or intracranial hematomas. High velocity impacts against the skull lead to comminuted fractures, blowout fractures, combined fractures of the skull and skull base or even fissures and bending fractures at the opposite side of the impact (Probst and Tomaschett 1990; Spangenberg et al.1997).

•Forces with a small impact surface on the skullcap can lead either to fissure fractures or to bending fractures in the base area (Ernst et al. 2004)

•Forces with a small impact surface on the facial skeleton may lead to bending fractures of the frontal skull base with dislocation of bone fragments into the cranium

The convexity of the skull, the anatomical stability of the diploic calvarial bone and the skull base form