Preoperative CT displacement predicts inferior alveolar nerve injury in mandibular fractures: a tool for clinical risk stratification

OBJECTIVES: The aim of this retrospective study was to determine the incidence of inferior alveolar nerve (IAN) injury in patients with mandibular fractures by correlating fracture displacement and mandibular canal involvement on preoperative computed tomography (CT) imaging with clinically documented nerve deficits - and to develop the first CT-based displacement classification for predicting the likelihood of IAN injury. MATERIALS AND METHODS: We retrospectively reviewed mandibular fractures and available preoperative CT scans. Fracture location, cortical and canal displacement, and nerve function were recorded. Receiver operating characteristic (ROC) curve and logistic regression analyses evaluated associations between displacement thresholds and IAN injury risk. RESULTS: A total of 208 patients (237 fractures) were included; preoperative IAN deficits occurred in 74/237 fractures (31.2%) and persisted at ≥ 6 months in 3/237 fractures (1.3%). ROC analysis yielded area under the curve (AUC) values of 0.71, 0.73, 0.75, and 0.75 for cortical displacement cut-offs of > 3.60 mm (transverse), > 1.68 mm (sagittal), > 1.29 mm (vertical), and > 9.61 mm (summed displacement), respectively. Multivariate logistic regression demonstrated that exceeding these thresholds was associated with significantly increased risk of IAN hypoesthesia - OR 6.4, 4.8, 6.8, and 7.9, respectively (all p < 0.001). Mandibular canal displacement showed limited predictive value for IAN hypoesthesia, with ROC AUCs of 0.63 (axial), 0.63 (coronal), 0.64 (sagittal), and 0.64 (summed displacement). CONCLUSION AND CLINICAL RELEVANCE: This study establishes specific, plane-based CT displacement thresholds that may help to identify mandibular fractures at high risk of IAN injury. Our proposed CT-based classification enables objective preoperative risk stratification, enhances patient counseling, guides surgical decision-making, and supports the standardized medico-legal assessment of potential permanent sensory deficits.