c-spine-interpretation

Mandibular Fractures

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This article provides an overview of mandibular fractures including relevant anatomy, aetiology, investigations, clinical features and management options.


Mandibular anatomy

The mandible is the bone of the lower jaw, carrying the lower teeth and forming part of the temporomandibular joint with the temporal bones of the skull. The main function of the mandible is to facilitate mastication (chewing) and all of the muscles of mastication attach to the mandible.

The main anatomical areas of the mandible are the symphysis, the parasymphysis, the body, the angle, the ramus passing upwards, the condylar process comprising the head and neck at the upper posterior aspect of the ramus, and the coronoid process, at the upper anterior end of the ramus (Figure 1 and 2).  The alveolar process is the part of the bone that bears the teeth, and this is resorbed when teeth are lost.

Nerves

The mandible is closely related to some important neurovascular structures that need to be considered when managing a patient with maxillofacial trauma.

Trigeminal nerve (CNV)

The trigeminal nerve is responsible for sensation to the face and for motor functions such as mastication. It has three branches – the ophthalmic, maxillary and mandibular branches. The mandibular branch of the trigeminal nerve (CNV3) exits the skull via the foramen ovale and the main trunk then divides into:

  • Motor branches to the medial pterygoid, tensor veli palatine and tensor tympani muscles
  • Sensory meningeal branch

The main branch of CNV3 then divides into an anterior and a posterior branch.

Anterior branch of CNV3

The anterior branch of CNV3 provides motor supply to the muscles of mastication and sensory supply to the inside of the cheek (buccal mucosa) via the buccal branch.

Posterior branch of CNV3

The posterior branch of CNV3 further divides into the auriculotemporal nerve, lingual nerve and inferior alveolar nerve.

The auriculotemporal nerve runs alongside the superficial temporal artery, providing sensation to the auricle, the external auditory meatus, the outer portion of the tympanic membrane and the skin in the temporal region. It also gives off a few branches that go on to supply the temporomandibular joint.

The lingual nerve lies on the medial aspect of the mandible and provides general sensation to the anterior two-thirds of the tongue. It is joined by the chorda tympani, a branch of the facial nerve, which provides taste sensation to the anterior two-thirds of the tongue.

The inferior alveolar nerve provides sensory supply to the lower teeth and, via its mental branch exiting at the mental foramen, the lower lip and chin. This nerve also provides motor innervation to the mylohyoid muscle and the anterior belly of the digastric muscle.

After branching off from the posterior division, the inferior alveolar nerve (and accompanying vasculature) enters the mandible at the lingula on its medial aspect. It runs through the inferior alveolar canal, providing sensation to the lower teeth. This can be seen on an orthopantomogram as a radiolucent channel inferior to the teeth (Figure 6, No. 15). Anteriorly, at approximately the first and second premolar teeth, the nerve emerges from the mental foramen, supplying sensation to the front of the chin and lower lip as well as the labial gingivae of the mandibular anterior teeth and the premolars.

The inferior alveolar nerve is one of the most important clinical considerations when assessing a patient with a suspected mandibular fracture. Mandibular fractures can traumatise the inferior alveolar nerve, leading to sensory deficits in the areas described above. Patients may volunteer that they feel numb but it is worth testing and comparing bilaterally by touching the patient’s lips and chin; any numbness should increase suspicion of an underlying mandibular fracture.

Facial nerve (CN VII)

The facial nerve’s principal function is to control the muscles of facial expression. The main trunk of this nerve with its two main divisions (temporofacial and cervicofacial) cross the mandibular ramus at the posterior border in the condylar neck region. The facial nerve has five terminal branches: the temporal, zygomatic, buccal, marginal mandibular and cervical branches. These can be injured in penetrating injuries, so it is important to carry out a facial nerve assessment when presented with these types of injuries in the head and neck.

Vasculature

The main blood supply to the mandible itself comes from the inferior alveolar artery, a branch of the maxillary artery, itself a branch of the external carotid artery. It supplies the pulps of the teeth, the chin, and the mylohyoid. There is also significant supply from the periosteum, particularly in older age. The facial artery, also a branch of the external carotid, crosses the inferior border of the mandible at the level of the anterior border of the masseter muscle and supplies a variety of structures in the face and neck via its facial and cervical branches.

Muscles of the mandible

There are many muscles that attach to and move the mandible. For the purposes of this article, they are included more for orientation relative to other structures, such as the relationship between the facial artery and the masseter described above. Full descriptions of all muscles of mastication and facial expression are beyond the scope of this article.

 

The four main muscles of mastication are the masseter, temporalis, and the medial and lateral pterygoid muscles. Unlike the majority of the facial muscles, the muscles of mastication are innervated by the trigeminal nerve, more specifically the mandibular division (CNV3). The masseter, temporalis and medial pterygoid muscles are responsible for jaw closure. The lateral pterygoid opens the mandible, assisted in this action in the initial stages by the digastric, mylohyoid and geniohyoid muscles. Lateral movements of the mandible are controlled by the pterygoid muscles; the movement of the mandible to the left involves the left lateral pterygoid and the right medial pterygoid.


Aetiology

Mandibular fractures are typically the result of assault and road traffic accidents, though fracture can occur as a consequence of falls, trips and sports. There is notable age, gender and indeed cultural/geographical inter-variability when looking at the pattern and incidence of mandibular fractures. Men are more likely to be involved in assaults; women more likely to suffer fractures secondary to trips and falls. Interpersonal violence is often the cause in Western cultures; road traffic accidents contribute more frequently in the Middle East.

They can be associated with overlying soft tissue injury/loss, such as in stabbings or gunshot wounds. Underlying hard tissue trauma must be identified or ruled out where there is soft tissue injury.

Classification

Typically, mandibular fractures are classified according to their site. This is useful as both the signs and symptoms as well as the management are often dependent upon the location of the fracture. As mentioned above, the mandible can be sub-categorised into different areas. The exact delineations are beyond the scope of this article, but the image below roughly highlights them.

Figure 5. Anatomical areas of the mandible. 3

The most common sites of fracture include the angle, parasymphysis and condyle. Coronoid fracture is very rare, accounting for about 1% of mandibular fractures (they are well-protected laterally by the zygoma). Anatomical location of fractures often reflects the cause. Interpersonal violence often results in angle fracture (imagine a blow to the side of the face) whilst falls typically result in condylar fracture (a fall onto the chin can drive the condyles into their fossae). Angle fractures usually occur through the wisdom tooth socket and parasymphysis fractures commonly through the canine socket. Bilateral condyle fracture is commonly accompanied by a true symphyseal fracture (midline) – a so-called Guardsman’s fracture, the result of falling on the point of the chin. Table 1 summarises the relative incidence and pattern of mandibular fractures.

Table 1. Incidence/pattern of mandibular fracture.

Anatomical area

Incidence (%)

Symphysis/parasymphysis

38.9

Condyle

26

Angle

14.3

Body

14.3

Ramus

6.6

Coronoid

1

 


Clinical features

Once cleared of all other life-, limb- or sight-threatening injuries (a visual acuity score is a prerequisite for an OMFS referral if mid-face trauma is also suspected), a more detailed history and examination of suspected mandibular fracture can take place.

Alongside the usual medical and social history, it is important to determine the date and mechanism of injury. There will likely be a history of trauma. The patient may report that they cannot bite their teeth together in a manner which is normal for them. Disturbances in the patient’s occlusion (how the teeth meet), as well as a sublingual haematoma, are almost pathognomonic for mandibular fracture. Any paraesthesia in the distribution of CNV3 is highly suggestive of mandibular fracture, as the inferior alveolar nerve, and its mental branch, supply sensation to the lower teeth, the lower lip and the chin. A bilateral comparison should be carried out and any discrepancies noted. Any suspicion of non-accidental injury may require safeguarding escalation; in children, this is usually determined from the history rather than the examination itself. Facial fractures in children occur less frequently than in adults as a result of an increased skull-to-face ratio, the extent of sinus development and the structure of the bone itself and underlying soft tissues.

Extraoral examination of the face may reveal bruising, swelling or lacerations over the fracture site. As above, any laceration and a history of trauma should raise suspicion of underlying bony injury. Be sure to examine the whole face for lacerations, including under the chin (submental). Lacerations can be missed here, particularly in those with significant facial hair. Palpation of the TMJs may cause acute pain, whilst gentle palpation of the mandible may reveal step deformities, crepitus and tenderness. Most patients with mandibular fractures have some degree of trismus secondary to pain.

Intra-oral examination may reveal haematomas, lacerations and blood-stained saliva. Gently clean/suction the mouth free of any clots and carefully examine the lingual (on the side of the tongue) and buccal (towards the cheeks) sulcus (the most inferior aspect of the gums on either side of the teeth). Palpation in both areas may reveal steps or deformities.

There may be evidence of current or prior bleeding from the sockets around the teeth, which is suggestive of open fracture. There may also be a “step” in the occlusion in the same areas. Gentle movement either side of the suspected fracture site may elicit mobility.

If teeth/dentures appear fractured, it is critical to ascertain if this is normal for the patient. If the patient cannot account for the location of any broken teeth/denture fragments, a chest X-ray is indicated to rule out aspiration.

Make careful notes of any findings, including which teeth you think are fractured or involved in the fracture.


Investigations

When a mandibular fracture is suspected, an X-ray should be performed as the first-line investigation. An X-ray is necessary for accurate diagnosis and can be useful in determining management (e.g. surgical approach to repair).

An orthopantomogram and a PA mandible are the essentials for assessment. CT may be indicated for more accurate surgical planning but this would usually be ordered by the OMFS team.

It is useful to know the normal structures you might see on an orthopantomogram.

Figure 6. Orthopantomogram and radiographic anatomy. 4
Mandibular fracture example

This series of images relate to a patient who suffered a fracture of the left angle of the mandible and right body of the mandible. The dashed line (Figure 7) represents the pharyngeal airspace which appears as a radiolucency on an orthopantomogram; it is sometimes misdiagnosed as a fracture. 

 


Differential diagnoses 

Possible differential diagnoses of a mandibular fracture include:

  • Pharyngeal airspace may be misdiagnosed as a mandibular fracture.
  • Superimposition of the pterygoid plates (No. 14 in Figure 6) may be misdiagnosed as a fracture of the mandibular coronoid processes.

Management

Initial management

As with any acute fracture, you should adopt an ABCDE approach as part of your initial assessment. If abnormalities are encountered, these should be dealt with appropriately.

Analgesia is often required to manage the significant pain associated with mandibular fracture.

Antibiotics should be administered if the fracture involves a tooth-bearing area (i.e. communicating with the oral cavity).

Patients with a suspected mandibular fracture should be urgently referred to the OMFS team for further assessment and management.

OMFS management

Further management by the OMFS team depends on many factors but some typical examples include:

  • Undisplaced, non-mobile fractures are typically treated conservatively.
  • Displaced or mobile fractures of the tooth-bearing region usually require open reduction internal fixation (ORIF).
  • Displaced condyles with angulation/overlap are usually treated with ORIF or intermaxillary fixation (arches, ligatures or screws which are attached to the dental arches).
  • Coronoid fractures are usually treated conservatively.

Typically, any fracture that does require surgical intervention is admitted and treated with ORIF followed by 6 weeks of soft diet and avoidance of contact sports for 3 months. In any case, this is a decision for the OMFS team but a good examination and referral can optimise the process.


Reviewer

Mhairi Little

OMFS Consultant

James Cook University Hospital


References

  1. Lorenzo Iafrate. Annotated skull images created for geekymedics.com.
  2. Lorenzo Iafrate. Licenced muscles of mastication images modified for geekymedics.com 
  3. AO Surgery Reference, www.aosurgery.org. Copyright by AO Foundation, Switzerland.
  4. Lorenzo Iafrate. Licenced OPG images adapted for geekymedics.com.
  5. County Durham and Darlington NHS Foundation Trust. Pre-operative orthopantomogram and PA mandible for use on geekymedics.com.
  6. South Tees Hospitals NHS Foundation Trust. Post-operative orthopantomogram for use on geekymedics.com. 
  7. Alcalá-Galiano A, Arribas-García I, Martín-Pérez M, Romance A, Montalvo-Moreno Juncos J (2008). Pediatric Facial Fractures: Children Are Not Just Small Adults. RadioGraphics 28:441-461.
  8. Cienfuegos R, Cornelius C, III E, Kushner G, Figari M, Aniceto G et al. (2020). AO Surgery Reference: Mandible. Available at: [LINK]
  9. Natu S, Pradhan H, Gupta H, Alam S, Gupta S, Pradhan R et al. (2012). An Epidemiological Study on Pattern and Incidence of Mandibular Fractures. Plastic Surgery International 2012:1-7.
  10. Rashid A, Eyeson J, Haider D, van Gijn D, Fan K (2013). Incidence and patterns of mandibular fractures during a 5-year period in a London teaching hospital. British Journal of Oral and Maxillofacial Surgery 51:794-798.

 

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