Microsurgical repair of the inferior alveolar nerve: success rate and factors that adversely affect outcome.

PURPOSE: The objectives of this study were to determine the likelihood of regaining functional sensory recovery (FSR) after microsurgical repair of the inferior alveolar nerve (IAN), and which variables significantly affected the outcome of that surgery in a large series of patients.
MATERIALS AND METHODS: This was a retrospective cohort study that evaluated all patients who had undergone microsurgical repair of the IAN by 1 of the senior surgeons (R.A.M.) from March 1986 through December 2005. The requirements for inclusion of a patient in the study included the availability of a complete chart record and a final follow-up visit at least 12 months after surgery. All other patients were excluded. The predictor variables were categorized as demographic, etiologic, and operative. The final outcome variable was the level of recovery of sensory function as determined by standardized neurosensory testing at the last postoperative visit of each patient and based on guidelines established by the Medical Research Council Scale. Risk factors for surgical failure to achieve useful sensory function were determined from analysis of descriptive statistics, including patient age, patient gender, etiology of nerve injury, chief sensory complaint (numbness, pain, or both), time from injury to surgical intervention (in months), intraoperative findings, and surgical procedure. Logistic regression methods and associated odds ratios were used to quantify the association between the risk factors and improvement. Receiver operator characteristic curve analysis was used to find the threshold of those variables that significantly affected patient outcome.
RESULTS: In total, 167 patients (41 male and 126 female patients; mean age, 38.7 years [range, 15-75 years]) underwent 186 IAN repairs (19 patients sustained bilateral IAN injuries). The mean time from injury until surgery was 10.7 months (range, 0-72 months). Successful recovery from neurosensory dysfunction (FSR, defined by the Medical Research Council Scale as ranging from useful sensory function to complete sensory recovery) was observed in 152 repaired IANs (81.7%). With increasing duration from date of injury to IAN repair, the likelihood of FSR decreased (odds ratio, 0.898; P < .001). The odds of achieving FSR exhibited a linear decline between the date of nerve injury and its repair, with a significant drop in rate of successful outcome (FSR) occurring beginning at 12 months after injury. There was also a significant negative relationship between increasing patient age and improvement (odds ratio, 0.97; P = .015), with a threshold drop of achieving FSR at 51 years of age. The cause of the injury, the operative findings, and the type of operation performed to repair the nerve had no significant effect on the likelihood of the patient regaining FSR. The presence of pain after nerve injury did not affect the likelihood of achieving FSR after repair in a statistically significant manner (P = .08). In those patients who did not have pain as a major complaint before nerve repair, pain did not develop after microneurosurgery.
CONCLUSIONS: Microsurgical repair of an IAN injury resulted in successful restoration of an acceptable level of neurosensory function (FSR) in most patients (152 of 186 repairs [81.7%]) in this study. The likelihood of regaining FSR was inversely related to both time between the injury and its repair and increasing patient age, with significant threshold drops at 12 months after nerve injury and at 51 years of age, respectively.