Refined Concept of Motor Supply to the Medial Periorbital Area Relevant to Periorbital Surgery

Background: Mimetic muscles in the medial periorbital area have been thought to be innervated solely by the angular nerve. Recently, however, the upper medial palpebral branch and lower palpebral branch were reported as additional motor suppliers in this area. This study aimed to define all the motor nerve systems passing through the medial canthal area. Methods: Motor nerve branches that passed through the medial canthal region were identified and traced thoroughly from the parotid gland to their destinations under a surgical microscopic field in 74 hemifaces. The courses, anatomical positions of, and anatomical relationships between the angular nerve and the upper medial palpebral branch were observed. Results: The upper medial palpebral branch and the angular nerve were found in all samples within a 3-mm to 6-mm area lateral to the intersecting point of the medial orbital rim and medial canthal ligament. The upper medial palpebral branch supplied the upper eyelid, whereas the angular nerve supplied the extraorbicularis muscles in the medial periorbital area. The medial pretarsal area of the upper eyelid was supplied solely by the pretarsal branches of the upper medial palpebral branch, which was formed by uniting three or four minor branches that traveled throughout the anterior cheek. Conclusions: Two separate motor nerve systems, the upper medial palpebral branch and the angular nerve, exist in the medial canthal area. The upper medial palpebral branch course along the medial orbital rim is considered as a facial nerve danger zone.