Mandibular fractures

"The mandible breaks like a polo mint"

It is important to understand how mandibles fracture. To gain an appreciation of this we must consider the shape of the mandible, muscles of mastication as well as the general shape.
When forces are applied to the mandible, zones of tension and compression are created. The superior portion of the mandible is a tension zone and the inferior portion is the compression zone. In terms of how the mandible will deform, this is largely dependent on the muscles involved in its movement, namely masseter, temporalis, lateral and medial pterygoid. The mandible is the strongest at the symphysis and weakest at the condyles.
Accounting for the fact the condyle sits in the glenoid fossa, if there is an impact to the body of the mandible, the force is transmitted to the condyles and due to their limitation of movement, they will fracture. Therefore, it is important to bear in the mind the direction of the impact e.g. if there is an impact on the right body of the mandible, look for a contralateral condylar fracture. Similarly, a bilateral condylar fracture may be indicative of a midline impact.
For this reason if you see if a parasymphysis fracture, always look for another fracture on the contralateral side. This is why surgeons say “The mandible breaks like a polo mint.”

Fractures of the mandible can also be characterised as favourable and unfavourable. This is largely determined by the location and extent of the fracture relative to the pull/contraction of the muscles. A favourable fracture is defined as passive reduction of the fractured components when the relevant musculature is engaged. Conversely, an unfavourable fracture is separation of the fracture when the relevant musculature is engaged.

Figure 1. Favourable vs unfavourable fractures [1]

Mandible fractures can also be categorised by type of fracture and it useful to know the terminology when you are describing the fracture to a senior:
1) Greenstick: Incomplete fracture, frequently seen in children
2) Simple: separation of the bone with no/minimal fragmentation
3) Comminuted: Bone has been fragmented usually in line with high velocity impacts
4) Open: the fracture communicates with the outside environment e.g. the mouth. If you have an angle fracture for example and it is not visible in the mouth but on the OPG you can see it is crossing or communicating with the PDL of the wisdom teeth this would be regarded as a open fracture

Signs and symptoms

• Numbness of the lip and chin (V3)
• Malocclusion e.g. open bite/premature contact
• Trismus
• Mobility of the fractured segment
• Haematoma in floor of mouth – this is pathognomonic of a mandibular fracture until proven otherwise
• Lacerations overlying fracture
• Anterior open bite
• Step between teeth either side of fracture (ensure no teeth are missing)

Figure 2. Clinical picture of a mandibular fracture [2]

Special Investigations

For a confirmed diagnosis of a mandibular fracture, you must have at least two views at right angles to each other. Therefore, the radiographic imaging of choice usually is an OPG and a PA mandible. Fractured condyles can be more difficult to identify radiographically, therefore it may be helpful to look for:
• Shortened condylar-ramus length
• Radiolucent fracture line
• Radiopaque density (overlapping of fractured segments)
• Premature contact on side of fracture
It is uncommon for CT scans to be taken for mandibular fractures however they can be taken in the following situations:
• Significant displacement/dislocation
• Significant communition
• Suspicion of mechanical obstruction caused by a condylar fracture
• Patient unable to sit or stand upright for OPG/PA mandible
• Suspected pathological fracture of mandible

Figure 3. PA mandible showing left
parasymphysis and contralateral
condyle fracture [3]

Figure 4. OPG showing left parasymphysis fracture [4]

Treatment

Mandibular fractures can be managed in a number of ways but can broadly be categorised into conservative/non-surgical and surgical management. Note open fractures are not treated conservatively most of the time.
To manage the fracture conservatively and successfully, it is dependent on several factors:
• Patient is dentate and has a normal occlusion
• Undisplaced fracture
• Favourable fracture with regards to location, extent and pull of musculature
• Good oral hygiene and compliance e.g soft diet
• Compliance with regular post-injury follow-up

Surgical management broadly involves two main treatment modalities.

Closed Reduction

This method involves the use of inter-maxillary fixation (IMF) which immobilises the fractured segments to allow for bony healing. This technique is reserved for favourable, closed fractures and in patients with a full dentition, stable occlusion and good compliance. It is also commonly used in unilateral condylar neck fractures.
Another method which can used for closed reduction is the usage of arch bars. The arch bars are secured to the teeth by wires which wrap around the teeth to hold the arch bars firmly in place. Elastic bands can be fitted between the top and lower jaws to manoeuvre the bite into the ideal position. They do not prevent you from opening your jaws. Arch bars are temporary and the length of time required is dependent upon their use. Typically trauma cases may require arch bars for two to four weeks before removal.

Figure 5.Arch bars following mandibular fracture [5]

Open Reduction and internal fixation (ORIF)

As with closed reduction, intermediary IMF is used in the form of screws which are wired together to demonstrate the correct occlusion when reducing the fracture (less frequently arch bars or the hand held approach). The approach used is dependent on the location of the fracture. Angle fractures tend to use a transbuccal approach once the fracture is exposed, symphysis/parasymphysis fractures can be exposed through a vestibular/crevicular incision. Large, rigid plates are used for comminuted fracture and these may need to be prepared pre-operatively in the lab. However in most cases, mini-plates are used to ensure reduction of the fracture site.
The anatomical placement and choice of plate for surgical reduction is governed by Champy's lines of osteosynthesis. The literature has demonstrated that two points of fixation (2 plates) provides greater stability than one as seen in Figure 7. The general principle suggests when the plates are placed along the ideal lines of osteosynthesis they provide maximum stability and proper osteosynthesis. Further reading is recommended on this topic.

What do you need to do?

Pre-operatively

• Ensure you have the relevant imaging – OPG + PA mandible
• Bloods – FBC, U&Es, Clotting screen, G&S
• Cannula
• Prescribe antibiotics in line with trust protocol e.g. 1.2g co-amoxiclav IV
• Prescribe analgesia and CHX mouthwash
• Consent (only consent for the procedure if you are competent to do so)

Post-operatively

• Post-op imaging – OPG + PA mandible
• Soft diet 4-6 weeks
• Continue IV antibiotics and prescribe oral antibiotics for the patient to take home
• Prescribe analgesia and CHX mouthwash on the TTO
• Provide education and elastics for those in IMF
• Follow-up in clinic

References

[1] Mandibular Fractures [Internet]. Ento Key. 2020. Available from: https://entokey.com/mandibular-fractures/
[2] Treatment Of Mandibular Fracture (Broken Lower Jaw) - PORTAL MyHEALTH [Internet]. PORTAL MyHEALTH. 2020. Available from: http://www.myhealth.gov.my/en/treatment-mandibular-fracture-broken-lower-jaw/
[3] Naeem A, Gemal H, Reed D. Imaging in traumatic mandibular fractures. Quantitative Imaging in Medicine and Surgery. 2017;7(4):469-479.
[4] Bhagol A, Singh V, Singhal R. Management of Mandibular Fractures. A Textbook of Advanced Oral and Maxillofacial Surgery. 2013;.
[5] Doran J. Arch Bars, Leonard Buttons & Inter-Maxillary Fixation Screws Removal [Internet]. Exodontia.info. Available from: http://www.exodontia.info/Archbar_Removal.html
[6] Anslem O, Eyituoyo O, Olabode O, Ademola O, Adesina A. A comparative study of intermaxillary fixation screws and noncompression miniplates in the treatment of mandibular fractures: a prospective clinical study. Oral and Maxillofacial Surgery. 2017;21(2):233-240.
[7] Facial Fracture Management Handbook - Mandible fractures | Iowa Head and Neck Protocols [Internet]. Medicine.uiowa.edu. 2020. Available from: https://medicine.uiowa.edu/iowaprotocols/facial-fracture-management-handbook-mandible-fractures