Room for Leeway; Margin of safety to Facial Nerve in Retro-auricular Trans-Meatal Approaches to Mandibular Condyles

Background: In maxillofacial surgery, accessing the mandibular condyle is a contested topic. Whilst retro-auricular approaches are considered to be protective of the facial nerve, the distance from dissection to nerve has not been verified. Methods: Dissection of 29 cadaveric head specimens was carried out using a retro-auricular approach. Three measurements were made: (a) from nerve to the inferior edge of the cartilaginous external acoustic meatus, (b) thickness of tissue laterally between dissection and nerve, and (c) thickness of tissue vertically between inferior limit of dissection and nerve. Intra-class correlation co-efficient (ICC) was used to assess inter-observer reliability. Results: The mean distance from the external acoustic meatus was 14.28 mm (ICC = 0.59). Inferior tissue thickness averaged 9.70 mm ( ICC = 0.42), and lateral tissue thickness averaged 7.17 mm ( ICC = 0.59). Inferior tissue thickness demonstrated the greatest inter-specimen standard deviation (3.09 mm) and lowest individual specimen measurements (0.99 mm). Conclusion: The retro-auricular approach remains safe for surgical access to the mandibular condyle. However, care should be taken of the inferior extent of the dissection once past the external acoustic meatus, particularly when supervising trainees.