Fractures of the mandible are common. However, the correlation between the severity of the fracture and the recovery of any associated inferior dental (ID) nerve injury is still poorly understood. We aimed to examine the relationship between the amount of fracture displacement and how it relates to the recovery of sensation to the lower lip. One hundred and fifty patients requiring treatment of a mandibular fracture (where the fracture passed across the ID canal) were assessed. One hundred were initially assessed in a retrospective double-blinded study. A further 50 patients were then followed up prospectively. Both the maximal displacement of the fracture and the displacement specifically at the ID canal were measured. Sensory recovery, or persistence of numbness, was also recorded for each patient. Although there appeared to be a correlation between increasing displacement at the ID canal and a poorer recovery, there was not a clear relationship between the two, and there were many exceptions. Persistent numbness (>1 year) still occurred in fractures with relatively minimal displacement (≤3 mm). Possible reasons for persistent numbness are discussed.
Mandibular fractures are common. Depending on a number of factors, treatment includes a soft diet and antibiotics, closed reduction such as with intermaxillary fixation (IMF), or open reduction and internal fixation (ORIF). In fractures that pass through the inferior dental (ID) canal, alteration of sensation is commonly seen. This may be temporary or permanent. Previous studies have shown that the degree of displacement of a mandibular fracture may have a negative impact on long-term neurosensory function. However, such assumptions regarding the presence of displaced fractures and subsequent paraesthesia have not been proved consistently. For example, one report demonstrated that displacement of mandibular fractures correlated only with preoperative paraesthesia but not with postoperative paraesthesia.
Commonly seen by orthopaedic surgeons, sensory or motor deficits associated with a fracture are an indication for urgent treatment. With fractures of the limb, this often begins in the emergency department with immediate reduction (e.g. by applying axial traction), followed by temporary support. Failure to do this can result in long-term dysfunction, for example humeral fractures and subsequent wrist drop. In the maxillofacial setting, motor nerve deficits are less frequently associated with fractures than sensory injuries. Nevertheless, the importance of sensory nerve function should not be underestimated – particularly in the face. This is generally not regarded as an indication for urgent reduction. Yet, sensory dysfunction in the face has significance in many daily activities, such as shaving, eating, talking, and kissing. Consequently, the prevalence of legal cases following assault and facial trauma is high; and unfortunately, sensory recovery may be complicated by iatrogenic injury during treatment, thereby placing the surgeon at risk from litigation as well.
We hypothesize that in fractures passing through the ID canal, greater displacement may correlate with a higher probability of prolonged sensory recovery and an increased likelihood of permanent numbness to the lower lip. We wish to determine if there are any predictive correlations, more specifically: (1) Is there a ‘threshold’ for displacement above which no recovery is a certainty but below which significant recovery is possible? (2) Is there a simple correlation between the degree of displacement and the prognosis for recovery (i.e. the more the fracture is displaced, the less chance there is of a full recovery)? (3) Is there no correlation between displacement and recovery other than due to mitigating or complicating circumstances?
Knowing the likely long-term risk of numbness based on a simple measurement taken from a preoperative radiograph would be highly valuable to the clinician. This radiological interpretation could assist the surgeon’s management as well as indicate the need for urgent reduction and fixation. Moreover, such evidence would aid the consent process and improve the advice offered to the patient.
Materials and methods
One hundred and fifty patients requiring treatment of a mandibular fracture were identified, all of whom fulfilled the criteria to participate. A retrospective, double-blinded study was conducted, with 100 patients being assessed in the initial period. A further 50 patients were then followed up in a prospective manner. The study was carried out over a 3-year period, with all of the fractures treated between 2009 and 2012 at our unit.
Inclusion criteria included: (1) At least one fracture passing through the ID canal (i.e. between the mandibular foramen and the mental foramen) on plain radiographs. Where two or more fractures were seen crossing the canal, the more displaced fracture was used for measurement. (2) Both postero-anterior (PA) and dental panoramic tomograph (DPT) views were required for analysis. (3) Patient follow-up was for a minimum of 12 months, or until there was documented full recovery of sensation, or when the recovery was sufficient to no longer adversely affect the patient.
Exclusion criteria included: (1) age <16 years (children); (2) patients with incomplete imaging or unrecorded data; (3) pathological fractures.
A double-blinded analysis was undertaken. One member of the team assessed fracture displacement, the other assessed the patient outcomes. Patient demographics, fracture details including the type of displacement, displacement at the ID canal, and details of sensory recovery, were all recorded into a database ( Table 1 ).