Displaced parasymphysis fracture after assault: assessment and fixation decisions
A 26-year-old man is brought to the emergency department after an alleged assault. He is alert, GCS 15, haemodynamically stable, with no vomiting or loss of consciousness. There is a 3 cm laceration over the left chin, swelling and tenderness over the left parasymphysis, and a palpable step in the 31–33 region. His teeth no longer meet as they did: there is an anterior open bite on the left and premature contact of the right molars. Mouth opening is 26 mm. Light touch sensation is reduced over the left lower lip and chin. There is no sublingual haematoma, no dysphagia, and the airway is patent. An OPG and CT facial bones show a displaced, mobile left parasymphysis fracture with about 6 mm displacement; both condyles appear intact. He is otherwise fit and well, takes no medication and smokes 10 cigarettes a day.
1. What must be assessed and excluded before you treat the fracture, and what does the malocclusion tell you?
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Primary survey first (ATLS): airway with cervical spine control, breathing, circulation, disability. A mandible fracture rarely kills, but a missed cervical spine injury or an expanding haematoma can. He has no airway signs now, but reassess for sublingual haematoma, floor-of-mouth raising, drooling and stridor, which indicate impending obstruction.
Exclude other injuries: clinical and radiological assessment of the upper face and zygomas, orbital floor, nasal bones, dentoalveolar segments, condyles and the cervical spine (OPG plus CT). Check for head injury and injuries elsewhere.
Local assessment: occlusal relationship, which teeth are present and restorable, teeth in the fracture line, periodontal status, and a documented inferior alveolar nerve sensory chart before any intervention. Check tetanus status and clean the chin laceration.
The malocclusion is the key finding. An anterior open bite on the left with premature right molar contact indicates the fractured fragment has been displaced by the muscles acting on it (mylohyoid, geniohyoid, digastric) and tells you the fracture is unstable and displaced. Restoring the pre-injury occlusion is the endpoint of treatment and the best intra-operative check that reduction is correct.
2. Compare closed treatment with open reduction and internal fixation for this fracture, and justify a recommendation.
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Closed treatment (maxillomandibular fixation for 4–6 weeks) relies on the occlusion to reduce the fragments. It works for undisplaced, favourable fractures and in children, and where surgery is unavailable. Its costs are prolonged liquid or soft diet with weight loss, poor oral hygiene, trismus and stiffness, relapse and malunion, difficulty managing the airway in an emergency, and poor tolerance in smokers and non-compliant patients.
ORIF through an intraoral vestibular approach: apply temporary MMF to establish the pre-injury occlusion, then fix with two 2.0 mm miniplates (or a single stronger plate) along Champy's lines - one at the inferior border in compression, one at the superior border in tension. It gives three-dimensional stability, earlier return to function and better hygiene, with lower rates of infection and malunion.
Recommendation: this is a displaced, mobile, unstable parasymphysis fracture with malocclusion and an associated chin laceration (a compound fracture). ORIF is indicated, ideally within 24–72 hours once swelling allows and after the primary survey. The laceration should be cleaned and closed; because the fracture is compound, a single pre-operative dose of antibiotics (for example co-amoxiclav) with a short post-operative course is reasonable, alongside chlorhexidine rinses and a soft diet.
3. What would you tell him about the numb lip and the other likely outcomes of treatment?
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Numb lip: reduced sensation in the inferior alveolar nerve distribution is common with displaced parasymphysis and angle fractures - reported in a substantial minority, up to a third or more in some series. Explain that the nerve has been bruised or stretched by the displacement, that most patients recover substantially over 6–12 months, and that a small proportion have permanent altered sensation. Document the pre-operative finding clearly, because it may otherwise be attributed to treatment. If it persists beyond 6–12 months, referral for specialist assessment is reasonable.
Other points to cover:
- Occlusion may need adjustment; he must keep to a soft diet for 4–6 weeks and avoid chewing on the operated side.
- Infection, plate exposure, plate removal (roughly 5–10%), and a chin scar.
- Smoking substantially increases infection and non-union - advise cessation and offer support.
- Rarely, non-union may require bone grafting.
- Warning signs: fever, increasing swelling, difficulty swallowing, neck swelling.
- Follow-up at 1, 2, 6 and 12 weeks with radiographs, documenting the occlusion at each visit.