Osteology of the facial skeleton and naso-ethmoidal complex in relation to trauma

Core Procedures

Surgical exposure of fracture articulations
Reduction of displaced facial fractures
Osteosynthesis of fracture sites

The facial skeleton provides a framework for housing the special senses of vision, taste and olfaction; the muscle attachment of the sphincters of the orbit and mouth; and the articulating apparatus that allows movement of the mandible against the maxilla to facilitate mastication.

Facial appearance and symmetry depend in part on the scaffolding effect of the facial skeleton that supports the overlying complex arrangement of soft tissue attachments (ligamentous, adipose and muscular).

In direct parallel with the bony orbit, the facial skeleton is made up of a complex arrangement of bones divided into a number of functional regions ( Fig. 4.1 ). Biomechanically, each of these regions responds in stereotypical ways to an escalation of energy transfer, which present different reconstructive aims and surgical objectives. With severe energy transfer there is extension of fracture configuration between these surgical zones; reconstruction of such injuries is therefore extremely complex.

Surgical surface anatomy

The craniofacial skeleton provides support for the muscles of facial expression, and ligamentous attachment and support for named collections of fat that modify facial appearance. The facial bones are relatively superficial in most individuals and bony landmarks may be palpated readily ( Fig. 4.2 ). Key landmarks enable the skin marking for anatomical incisions appropriate for the surgical exposure of fracture sites. The landmarks for the mandible include the symphysis, lower border, angle and temporomandibular joint (TMJ); collectively, they facilitate skin marking of approaches to the entire lower border of the mandible and the neck of the condyle. The lateral canthus of the eye and palpation of Whitnall's tubercle facilitate identification of the frontozygomatic suture, a key surgical fixation site in both lateral and central fractures of the middle third of the face. The supraorbital and infraorbital margins must be sought during physical examination to diagnose fractures of the orbit. The zygomatic projection and zygomatic arch are superficial and readily palpated.

Three foramina (supraorbital, infraorbital and mental) transmit sensory nerves. These foramina may be identified on each side by a line drawn from the supraorbital notch and the junction of the medial and middle thirds of the supraorbital rim (which is palpable) through to the region between the lower premolar teeth. At rest, the maxillary incisors are covered by the upper lip, which lifts 2–4 mm on smiling.

Surgical anatomy and classification of fractures of the mandible

The mandible articulates with the temporal bone at the TMJ ( Ch. 10 ). Surgically, the mandible is subdivided into anatomical regions ( Fig. 4.3 ) that fail in stereotypical ways when subjected to an increasing volume of energy transfer: the consequences of these failures are fixed according to standardized protocols. Muscle attachments are consistent and the action of the muscles directly influences the magnitude and direction of bony displacement.

$Fig. 4.3, Anatomically, the mandible may be divided into eight segments: condyle (purple), coronoid (brown), ramus (yellow), angle (orange), body (red), parasymphysis (green), symphysis (blue) and dentoalveolar (not coloured). The inherent tension, torsion and compression forces are unique for each segment. Fractures anterior to the angle involving the dentoalveolar segment are classed as compound fractures.$

Disturbance of the anatomical integrity of the mandible produces an established constellation of physical signs. The inferior alveolar nerve emerges from the infratemporal fossa, enters the mandible at the mandibular foramen and passes ventrally to exit at the mental foramen. Any fracture between these two foramina is likely to cause a neurological deficit manifest by altered sensation of the lower lip and chin up to the midline.

In dentate patients, fractures passing through the periodontal ligament are de facto compound to the oral cavity and therefore at risk of infection. Displacement of fractures through the alveolar bone causes pathological mobility of the affected teeth, and loss of the three-dimensional anatomy compromises the dental occlusion. Subperiosteal bleeding is common with extension into the lingual soft tissues; a sublingual haematoma is pathognomonic of a fracture of the mandible. The stability of a fracture depends on a number of factors: an intact periosteum; the degree of comminution of the fracture articulations; the number of fractures; and the direction of the fracture lines.

Favourable and unfavourable fracture patterns

Following cortico-cancellous disruption, the mandible will demonstrate abnormal mobility across the fracture site. The degree of instability and subsequent displacement depends on the direction of the fracture, which is influenced by the vector of muscle action.

The historical discussion of favourable versus unfavourable fractures was highly relevant when established treatment was intermaxillary fixation (wiring the jaws together using interdental fixtures) but is less relevant in contemporary surgical practice where the imperative is toward anatomical fixation using titanium bone plates. The terms horizontal and vertical are defined from the viewpoint of the observer ( Figs 4.4 and 4.5 ). Horizontally favourable fractures extend from the upper border of the mandible downward and forward; unfavourable fractures run from the upper border downward and backward, and the displacement is influenced by the elevators of the mandible, masseter and temporalis. Vertically favourable fractures run from the buccal plate anteriorly and backward through the lingual plate; unfavourable fractures run from the lingual plate posteriorly to the buccal plate. Medial pterygoid exerts a significant displacing force. Displacement is more common when there are both vertically and horizontally unfavourable fracture lines.

$Fig. 4.4, The fracture characteristics of the mandible in the horizontal (sagittal) plane. The orange fracture line has no body resistance or undercut on the superior margin to withstand the tendency of masseter to lift the proximal fragment. The blue line depicts a favourable fracture pattern. The actions of masseter are illustrated by the green arrow which will impact upon the stability of the fracture pattern.$

$Fig. 4.5, The orientation of the fracture in the vertical (axial) plane will determine whether the proximal fragment of the fracture will be displaced medially by medial pterygoid. The blue line represents a favourable fracture with the most proximal bone lingually on the distal fragment preventing displacement. A fracture along the orange line will predispose to displacement. The actions of the pterygoid muscles are illustrated by the green arrows which will impact upon the stability of the fracture pattern.$

Combination mandibular fracture

The mandible is a ring-type structure, which means that there is a high probability of synchronous fractures, and therefore a second fracture must be actively sought. Typically, there will be a primary ‘direct’ fracture and a secondary ‘indirect’ fracture. The common combination fractures occur at the parasymphysis and contralateral condylar neck or angle.

High-energy mandibular fractures

Escalation of energy transfer across the mandible changes the fracture pattern from that of a simple linear nature with predictable combinations to unpredictable segmentation of fracture articulations and multiple different fracture sites. Of particular surgical significance is segmentation of the lower border of the mandible, a biomechanically strong structure, which dictates the fundamental approach to reconstruction. Sagittal splitting of the buccal and lingual cortices results in a very unstable construct and surgical reconstruction requires a more robust superstructure ( Figs 4.6 and 4.7 ).

$Fig. 4.6, A high-energy mandibular fracture. Note the long length of the fracture paths (orange arrows), which are atypical and extend along the biomechanically robust areas. There is segmentation of the lower border.$

$Fig. 4.7, Inferior view of the mandible shown in Fig. 4.6 demonstrating a fractured and segmented lower border (orange arrows), a displaced fractured condyle (green arrows) and splitting of the buccal and lingual cortices (blue arrows). This fracture pattern is highly complex and difficult to reconstruct.$

Osteosynthesis of the mandible

The muscle attachments of the mandible cause zones of tension and compression across a fracture site that influence the efficiency of osteosynthesis. This phenomenon was first described by Michelet and Champy, and are well known to surgeons as Champy lines ( Fig. 4.8 ). It is essential to understand that the mandible anterior to the mental foramina is subject to both lateral and rotational forces and so it is necessary to equalize these forces with two plates. Fractures of the parasymphysis require a miniplate above the mental foramen and one below, procedures that are technically challenging. There is often a loop of the mental nerve anteriorly that may be damaged inadvertently by passing a screw to the canal. Fractures of the body and angle of the mandible can be managed predictably with a single mandibular plate.

$Fig. 4.8, Champy's lines (orange broken lines). Masticatory forces impose tension, compression and torsional forces on the mandible. A single osteosynthesis plate on the tension line in the body and angle region in linear fractures in a dentate patient provides adequate fixation. Two plates are advised anterior to the mental foramen and in the condylar segment to address the additional torsional forces.$

Failure of fixation is predictable; there are several patient- and management-related aetiological factors. Complex fractures involving tissue loss and pathological lesions may be managed by more rigid fixation involving bicortical fixation and screws that lock into both the bone and the plate itself.

Intraoral access to fractures of the body, angle and symphysis can be achieved with a linear buccal mucoperiosteal incision down to the fracture. The incision should be 3–5 mm below the mucogingival junction to aid suture closure. With fractures involving the parasymphysis, the mental nerve must be protected. The nerve exits the mental foramen approximately 5 mm apical to the root apices of the first and second premolars; occasionally there are two foramina. An incision anterior or distal to the premolar region will allow blunt dissection and identification of the mental foramen and protection of the nerve prior to completing the incision superior to these structures. Care must be taken not to avulse the nerve through excessive retraction. Periosteal and perineurial release will allow further mobility.

Fragility fracture of the mandible

Loss of dental tissue will result in loss of the bone associated with the teeth, and ultimately to a mandible consisting of the bare skeletal basal bone construct; fractures of this bone produce some of the most unpredictable patterns to manage surgically. There is a variation in the amount of resorption observed in the edentulous mandible. Height directly influences prognosis: the thinnest mandibles demonstrate the poorest prognosis with failure of bone union. The atrophic mandible is subject to the same vectors of muscle pull as in the dentate mandible, but because of the relatively reduced surface area at the fracture site, these patterns tend to be extremely unstable. Bruce recognized the poor outcomes likely after fixation and demonstrated in his retrospective and prospective studies that prognosis was worse in the more atrophic mandibles. This concept was refined by Luhr, who designated three groups that predicted prognosis and influenced fixation techniques ( Fig. 4.9 ).

$Fig. 4.9, A three-dimensional CT scan of a bilateral fracture of an edentulous mandible, known as a ‘bucket-handle’ fracture. The injury has resulted in telescoping of the mandible and loss of support for the insertions of the genioglossi, with subsequent loss of the airway; hence the need for intubation. Blue and purple arrows indicate a split maxillary fracture, which is not formally defined by the Le Fort classification.$

Fractures of the mandibular condyle

The temporomandibular (glenomandibular) joint is diarthrodial: that is, it is subdivided into upper and lower joint spaces by a fibrocartilaginous articular disc ( Ch. 10 ). The mandible enjoys a unique freedom of movement because this arrangement allows each joint to rotate and translate in concert with the contralateral articulation.

The TMJ should be considered as part of an anatomical unit that consists of the articular surface of the mandibular condyle and the ramus of the mandible, known as the ramus–condyle unit (RCU). This concept is central to the management of condylar fractures because reconstruction of the joint must restore not only the articulation, but also the posterior vertical height of the mandible. Historically, these injuries were managed by re-establishing the dental occlusion by wiring the maxillary and mandibular teeth together and thereby ‘controlling the malunion’ of the RCU.

Classification of fractures of the RCU

Fractures of the RCU have been classified in a number of ways but none has achieved universal acceptance and international implementation. Important factors related to management strategies that were initially summarized by Lindahl take into account the location of the fracture, the degree of displacement of the fracture, and whether or not the head of the condyle is in the glenoid fossa. The integrity of the condyle–ramus height and of the TMJ relates to the preservation of the lateral pole of the condylar head. Long-term, fractures of the medial pole alone, with or without displacement, may minimally compromise this arrangement. However, where fractures run within or lateral to the lateral pole there is a threat to ipsilateral TMJ function and the vertical height of the condyle–ramus. Open reduction and fixation of the latter is advised to limit TMJ disability and malocclusion ( Figs 4.10 and 4.11 ).

$Fig. 4.10, Classification of condylar fractures. A line is placed tangentially along the posterior border of the ramus and condyle (blue line) and a second line is placed perpendicular to this line, passing through the sigmoid notch (yellow line). When more than 50% of the fracture line is above the perpendicular line (green line), a high condylar fracture or neck fracture is diagnosed. Low condylar or condylar base fractures are fractures in which more than 50% of the fracture is below the line (orange line). Diacapitular or intracapsular fractures are fractures above the condylar neck.$

$Fig. 4.11, Intracapsular or condylar head fractures. Fractures running through the lateral pole (yellow and orange lines) predispose to functional disability of the temporomandibular joint and loss of condylar height. Multifragmented or severely dislocated or displaced fragments may predispose to avascular necrosis. The blue line divides the condyle into lateral and medial poles.$

The displacement of the fracture can be described in terms of shortening of the neck of the condyle and angulation. Attempts have been made to quantify these parameters to influence the decision to operate; with increased surgical experience it has been recognized that more predictable results are achieved even with small displacements.

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