Predicting the course of the marginal mandibular nerve: an evaluation of surgical landmarks

Abstract

The inferior branch of the marginal mandibular nerve (IMB) is at risk of injury during surgical neck dissections due to its variability. Often surgeons rely on a two‐finger breadth, and/or 2cm distance below the inferior border of the mandible for submandibular incision placement (Witt, 2006). The purpose was to evaluate the accuracy of the landmarks and to define other fixed landmarks to avoid IMB injury. In ten Thiel embalmed specimens, six independent raters palpated/pinned the inferior border of the mandible and a line two‐finger breadths below. Each pinhead was digitized (Microscribe®) and a superficial musculoaponeurotic (SMAS) flap was raised using a Ridson approach. The IMB was identified and digitized from the parotid gland to the depressor anguli oris/labii inferioris. The digitized data were modeled (Autodesk Maya®) and distances between the IMB and landmarks quantified. The distance from the IMB to the inferior border of the mandible varied from 2.5–11.5mm (7.5±2.9) suggesting that in some cases the 2cm landmark may be risky. The two‐finger breadth line to the IMB was 18.9–38.2mm (30.6±7.2) indicating adequate clearance for the nerve. Other landmarks have been documented. To avoid injury of the IMB during surgical neck dissections, easily measurable and reliable bony landmarks should be identified which can accurately predict the course and distribution of the nerve.