Does encountering the facial nerve during surgical management of mandibular condylar process fractures increase the risk of facial nerve weakness? A systematic review and meta-regression analysis.

PURPOSE: The purpose of this study was to identify whether the incidence of systematically identified or incidentally encountered facial nerve branches during dissection to approach condylar fractures increases risk of transient and/or permanent facial nerve weakness.

METHODS: A systematic review and meta-analysis were performed that included several databases with specific keywords, a reference search, and a manual search for suitable articles. The inclusion criteria were all clinical trials, with the aim of assessing the rate of facial nerve injuries when open reduction and internal fixation (ORIF) of condylar process fractures was performed using different surgical approaches. The articles had to have documented the number of encountered facial nerve branches during ORIF. The main outcome variable was transient and permanent facial nerve injury. The dependent variable was the event and/or number of encountered facial nerve branches during surgery, and how they were handled (i.e. dissected, retracted, etc.).

RESULTS: A total of 1202 mandibular condylar fractures were enrolled in 29 studies. Rate of transient facial nerve injury (TFNI) was 11.3 % (136/1202). The number of facial nerve branches encountered intraoperatively was 543, namely buccal, marginal mandibular, zygomatic and temporal nerve branches. There was a significant correlation suggesting that there is a strong positive linear relationship between TFNI and encountered facial nerve branches (Coef = 0.1916, P = 0.001). There was no significant relationship between permanent facial nerve injury and encountered facial nerve branches (P = 0.808). TFNI was 4.3% and 18.7% for those studies expressly reporting that facial nerve branches were encountered incidentally without dissection and with dissection, respectively. For studies reporting deliberate and systematic facial nerve dissection, TFNI was 20.9%. Finally, studies that did not report any encounters of facial nerve branches, TFNI was 7.9 %.

CONCLUSION: This meta-analysis demonstrated that manipulation of the facial nerve during different surgical approaches causes different incidences of facial nerve injury. The choice of surgical approach for a given fracture should take this into consideration.