Parasymphysis Fracture

Parasymphysis fracture is a fracture of the mandible between the mental foramen and the distal surface of the lateral incisor or canine, lying beside the midline symphysis. It makes up about 15 to 20% of mandibular fractures.

It is frequently caused by a direct blow, a fall or a road traffic collision, and is commonly associated with a contralateral condylar or angle fracture, because of the mechanical pattern. A bilateral parasymphyseal fracture produces a floating anterior segment.

Pathophysiology. The canine root is long and the bone in the area is thin around it, so fractures arise there. The pull of the suprahyoid and mylohyoid muscles distracts the fragments.

Tension at the alveolar border and compression at the inferior border are characteristic, so fixation must counter this. A bilateral fracture allows the tongue and floor of the mouth to fall back and risk airway obstruction.

Pain and swelling over the chin, a step in the lower border and the dental arch, malocclusion with an open bite or a gap between teeth, mobile fragments, bleeding from the gingival tear, lip and chin numbness (mental nerve), sublingual haematoma, and pain on moving the jaw.

Bilateral fractures show loss of the chin contour, tongue base displacement and a risk of airway obstruction when supine. Teeth in the fracture line may be mobile or fractured.

Airway compromise, bilateral fractures with a floating segment, associated condylar fractures, head injury or neck injury need urgent assessment.

• Panoramic radiograph, with an occlusal view or posteroanterior mandible view. CT of the facial bones for complex, multiple or comminuted injuries.
• Examination of the occlusion, teeth in the fracture line, lip sensation and tongue position.
• Assessment of the airway and cervical spine.
• Check for a contralateral condylar or angle fracture.
• Tetanus status.

Differential diagnosis.

• Symphysis midline fracture
• Body or angle fracture
• Condylar fracture
• Alveolar or dentoalveolar fracture
• Pathological fracture through a cyst or tumour
• Soft tissue haematoma
• Dislocated or avulsed teeth

• Airway protection first. Bilateral or comminuted fractures need careful positioning (sitting forward), and anaesthetic input for intubation.
• Open reduction and internal fixation: two miniplates, one at the inferior border and a second at the superior border (tension band) with monocortical screws that avoid the tooth roots and mental nerve. A reconstruction plate or a lag screw is an option for oblique fractures and in comminution.
• Arch bar or intermaxillary fixation to set the occlusion during surgery, removed at the end or kept for 1 to 2 weeks.
• Undisplaced fractures: closed treatment with a soft diet and a short period of intermaxillary fixation, or with an arch bar and elastics.
• Remove teeth in the fracture line if they are infected, mobile, fractured or interfering with reduction, and retain them otherwise.
• Antibiotics: amoxicillin with clavulanic acid 1.2 g intravenously every 8 hours as a first dose before surgery and for 24 hours, then no routine extension unless infection exists, when 625 mg orally three times daily is used for 5 to 7 days. Clindamycin 600 mg intravenously every 8 hours in penicillin allergy. Reduce the dose of amoxicillin with clavulanic acid when eGFR is under 30.
• Tetanus toxoid 0.5 mL intramuscularly if vaccination is incomplete or the last dose was over 10 years ago, with tetanus immunoglobulin 250 IU intramuscularly (500 IU after 24 hours or heavy contamination) when status is unknown or incomplete.
• Analgesia: paracetamol 1 g every 6 hours (maximum 4 g daily) with ibuprofen 400 mg every 8 hours with food when appropriate. Chlorhexidine 0.2% mouthwash 10 mL twice daily.
• Soft diet for 4 to 6 weeks. Complications: infection, wound dehiscence, malocclusion, mental nerve numbness, and tooth devitalisation.

Monitoring. Review at 1 week, 2 weeks, 6 weeks and 3 months for occlusion, wound, infection, sensation and tooth vitality, with a radiograph at 6 weeks.

Referral and escalation. Refer to oral and maxillofacial surgery. Urgent referral for airway compromise, bilateral fractures, infection or other facial fractures.