Evaluation of clinically relevant landmarks of the marginal mandibular branch of the facial nerve: A three-dimensional study with application to avoiding facial nerve palsy

摘要

Injury to the marginal mandibular branch of the facial nerve (MMN) during surgery often results in poor functional and cosmetic outcomes. A line two finger breadths or 2 cm inferior to the border of the mandible is commonly used in planning neck incisions to avoid injury to the MMN. The purpose was to compare the two finger breadth/2 cm landmarks in predicting MMN course, and their accuracy/reliability. Thirty-one cadaveric specimens were scanned to obtain 3D surface topography (FARO (R) scanner). Four independent raters pinned the inferior border of the mandible and a two finger breadth line and 2cm line below. The location of each pin was digitized (Microscribe). A preauricular flap was raised, and MMN branches were digitized and modelled (Geomagic (R)/Maya (R)) enabling quantification of the accuracy of these landmarks. The location of the two-finger breadth line was variable, spanning 25-51 mm below the inferior border of the mandible (ICC=0.10). The most inferior MMN branch did not pass below the two-finger breadth line in any specimen, but a narrow clearance zone (5 mm) was found in two. In contrast, in 7/31 specimens, the most inferior MMN branch coursed below the 2 cm line and would be at risk of injury. It was concluded that an incision two finger breadths below the inferior border of the mandible could provide safer access than the 2 cm line. After an incision has been placed using the two finger-breadth landmark, caution must be exercised during dissection as branches of the MMN may lie only a few millimeters superior to the incision. Clin. Anat. 29:151-156, 2016. (c) 2015 Wiley Periodicals, Inc.