Location of the mandibular branch of the facial nerve according to the neck position.

The aim of this study was to elucidate the exact location of the mandibular branch of the facial nerve according to different neck positions. Twenty-two hemifaces of 11 fresh human cadavers were used (age range, 53-89 y; mean age, 72.3 ± 10.5 y; 8 men and 3 women). Working through skin windows, the distance from the mandibular border to the mandibular branch of the facial nerve (border-nerve distance or BND) was measured at 3 points: (1) the mandible angle (gonion or Go point), (2) the point where the mandibular branch of the facial nerve crosses the facial artery (FA point), and (3) the one-fourth point from the gonion to the menton (1/4 point). Threads were hung on the skin windows along the mandibular border. With the neck in the neutral position and then full flexion (15 degrees), extension (15 degrees), and left and right rotations (30 degrees), the distance of the mandibular branch from the thread of the mandibular border was measured using calipers. In the neutral position, the mandibular branch was 3.50 ± 2.82 mm above the mandibular border at the Go point, 5.34 ± 2.98 mm above the mandibular border at the FA point, and 5.28 ± 1.86 mm above the mandibular border at the 1/4 point. At all 3 points, flexion or extension of the neck did not significantly move the mandibular branch. At the Go point and FA point, there was no significant difference between the ipsilateral rotation position and the contralateral rotation. Yet at the 1/4 point, the BND decreased (4.32 ± 2.60 mm) with the neck in ipsilateral rotation and the BND increased (5.97 ± 2.62 mm) with the neck in contralateral rotation. There was a significant difference between the ipsilateral rotation position and the contralateral rotation position (P = 0.020, t-test). Surgeons should keep in mind that at the 1/4 point, the mandibular branch of the facial nerve moves downward 1.10 ± 1.42 mm with the neck in ipsilateral rotation and moves upward 0.49 ± 1.84 mm with the neck in contralateral rotation.