a strong spherical structure. The traumatic force is absorbed and dispersed. Thus, skull base fractures will lead to fracture lines extending into the calvaria or, vice versa, fractures of the calvaria extend into the skull base. However, fractures of the cranium normally do not continue into the midface region. Bending fractures in the frontal bone region typically process as impression fractures towards the region of the crista galli, the cribriform plate or ethmoidal bone and the orbital roof, thus directing traumatic energy to the facial skeleton.

4.2  Frontofacial: Frontobasal Fractures

4.2.1  Fracture Mechanism

Forces acting directly on the frontofacial skeleton lead to fractures of the thin bony plates in the frontal skull base. The structural difference in thickness and elasticity of the skull bone varies in each individual. The bony struts fracture or disrupt at the connecting sutures with the facial skeleton, whereas the thin bone plates of the frontal skull base will be splintered to fragments.

In frontofacial trauma, mainly the roof of the ethmoidal cells, the medial wall, and floor of the orbits are affected (Probst 1971; Probst and Tomaschett 1990). In 78% of the cases, the system of the paranasal sinuses close to the skull base is involved (Probst 1971, 1986). In severe trauma, the optic nerve canal and the sphenoid bone can be involved (Kessel et al. 1971; Probst 1971; Dutton and Al Qurainy 1991) Rohrbach et al. 2000)

In such a trauma the medial aspect of the sphenoid cap is exceptionally endangered. Here, the thin osseous plate of the lamella orbitalis of the sphenoid is connected with the cribriform plate and the orbital part of the frontal bone (Boenninghaus 1974; Probst 1986; Theissing 1996). In comparison with the thin bony structures of the orbital walls, the bony structure of the cribriform plate and the crista galli are relatively strong. This is the anatomical explanation for fracture lines encircling and dislocating the ethmoid complex “en bloc” (Probst 1971; Mathog 1992; Mathog et al. 1995).

This kind of injury mechanism is often seen in traffic accidents and extreme falls (Probst and Tomaschett 1990; Spangenberg et al. 1997), but only rarely in sport (Panzoni et al.1983; Crow 1991; Gassner et al. 1999) or occupational accidents (Hill 1982; Hill et al. 1984).

A rare, but typical fracture mechanism leading to severe, life-threatening injuries occurs with boxing: the so-called “upper-cut.” A direct punch aimed at the chin or nose inferiorly can result in a fracture of the central part of the anterior skull base in the region of the cribriform plate with dislocation of bony fragments into the anterior cerebral fossa.

4.3  Midfacial: Frontobasal Fractures

The midface is defined as the connecting link between the frontobasal and maxillo-mandibular compartment. The aerated paranasal sinuses, the nasal passage and the orbits are energy absorbing structures protecting the skull base and the brain from direct trauma. Central and centro-­ lateral midface fractures can be associated with fractures of the walls of the frontal sinus. The frontal and/or posterior wall of the sinus may be affected.

High midface fractures can be associated with fractures of the frontal skull base. They occur as isolated complex nasofrontal fractures. The strong basis of the nose is dislocated into the anterior and middle part of the ethmoidal cells. Naso-orbito-ethmoidal (NOE) injuries with a severe impact on the high midfacial level may result in a dislocation of the crista galli and the cribriform plate into the anterior cranial cavity. This complicated injury is often seen in severe comminuted midface fractures (Lädrach et al. 1999).

•Fractures extend as direct bending fractures and as indirect burst fractures into the frontal skull base, the walls of the frontal sinus, into the frontal calvarial bones, but also towards the temporal bone

4.3.1  Trauma Factors

The severity of skeletal midfacial injuries is determined by a combination of various factors (Endo 1966; Bowerman 1985; Haskell 1985; Rowe and Williams 1985; Hardt et al. 1994). The localization, extent, and eventual damage to the visceral cranium depend on the impact force, the vector of the force, the impact point or contact area, and the level at which the injury is inflicted.

The potential damage is also determined by the form, surface structure and size of the injuring object, as well

as depending on the resistance and energy absorption of the skeletal structures, and the position of the head in the moment of the accident. Corresponding to the factors mentioned above, one can distinguish different patterns of injuries to the midface skeleton.

4.3.2  Impact Forces and Vectors

The skeleton of the midface is resistant to enormous forces approaching the midface region from below as the mandible absorbs a part of the traumatic energy.

Impact vectors that hit the midface from a craniocaudal or lateral direction can lead to shear fractures dislocating parts of the midface or the complete midface complex.

Massive forces with an impact vector directed horizontally towards the midface result in comminuted fractures pushing the bony midface framework against the strong bone extensions of the skull base, e.g., the sphenoid bone. The whole midface complex can be separated from the skull base and dislocated en bloc backwards and downwards. The typical clinical appearance is called “dish-face deformity.”

Impact vectors directed at the infranasal region can result in fractures of the anterior alveolar process, but also in Le Fort I fractures, sometimes in combination with sagittal split fractures of the maxilla.

Impact vectors from a superior direction towards the upper part of the midface in most cases result in dislocated fractures of the NOE complex, if the head is in a normal position. This may be so if the contact surface is small, otherwise it might also lead to a shear fracture of the midface complex on the Le Fort III level.

Impact vectors from a lateral direction towards the midface typically lead to fractures of the zygomatic complex. Depending on the cranial or caudal direction of the vector a cranial rotation or caudal dislocation of the zygomatic complex may result. The zygomatic arch absorbs energy directed against the posterior aspect of the lateral midface. Depending on the energy applied, unilateral Le Fort II fractures may result in a combination of fractures of the orbital floor and the lateral alveolar process of the maxilla. Usually the lateral midface block rotates around a sagittal axis.

Horizontal impact forces may result in fractures of the lateral midface with extensions towards the nasomaxillary complex and the zygomatico-orbital complex.

The zygomatic arch may be broken down. Mild, but punctually directed forces can lead to isolated fractures of the homolateral alveolar process (Rowe and Williams 1985).

If the head is fixed at the moment of impact to the skull, laterally applied forces can result in fractures of the lateral skull bone in the region of the infratemporal fossa. As a rule, the zygomatico-maxillary complex is then impressed with a clear rotation around a vertical axis or central dislocation.

4.3.3  Structural Resistance and Energy

Absorption

The impact energy is absorbed in different ways by the bony and soft tissue structures of the midface. The absorption is based on a variable bone resistance and strength as well as on the projection of the head at the moment of the impact (Nahum 1975; Hoffman and Krause 1991). A great variety of fracture patterns occur in the subcranial compartment related to the affecting kinetic energy (Rowe and Williams 1985; Bowerman 1985) (Fig. 4.1).

The following graphic illustration shows different absorption models. The magnitude of the kinetic energy applied has a direct influence on the fracture pattern, respectively to which extent the impact force can be absorbed by the midface complex (Fig. 4.2).

4.3.3.1  Degrees of Absorption

•Degree 1: A frontal impact with moderate force will result in multiple fractures of the prominent anatomical structures of the nasal complex and the midface. The central dislocation of fractured elements of the midface will absorb energy and helps to avoid skull base fractures

•Degree 2: In a frontal impact with considerable force, tear-off fractures and comminuted fractures of the anterior upper midface complex will occur, involving the naso-ethmoidal structures and sometimes the skull base

•Degree 3: Excessive force on frontal impact may result in comminuted fractures of the anterior and posterior upper midface complex

According to Lädrach et al. (1999), there are two different categories of complex cranio-orbito-maxillary fractures possible:

•Type I concerns a complex fracture that is limited to the external midface structure (no injury of the skull base)

•Type II (high-velocity trauma) concerns fractures of the external and internal midface structures, including­

tear-off fractures of the midface complex, comminution of the bony midface framework and central dislocation of the anterior and posterior midface column with multi-fragmentary fractures of the skull base. Intracranial injuries may result. Type II fractures can lead to multiple dural lacerations, brain damage and herniation of the cerebral tissues into the paranasal sinuses or even the orbits (Fig. 4.3)