The effect of a Le Fort I incision on nose and upper lip dynamics: Unraveling the mystery of the "Le Fort I lip".

Introduction: Postoperative flattening of the upper lip with loss of lip pout and down turning of the corners of the mouth is often seen after Le Fort I surgery. We aim to determine which facial muscles are involved in this phenomenon to update the literature on this subject.

Methods: In 6 cadavers, a unilateral Le Fort I incision was executed. After removal of the skin, all individual facial muscles were identified and submitted to bilateral tactile traction, comparing incised sides with non-incised sides.

Conclusion: All the components of the deep layer of the modiolus alae nasi (transverse part of the nasalis muscle and the myrtiformis muscle) and the deep layer of the midface musculature (levator anguli oris muscle) were transected by the Le Fort I incision. After performing the incision, the majority of the depressor septi nasi is intact. Further, the superficial layer of the midface musculature is intact but it loses tension because of its connection to the deep layer. This study suggests the importance of correctly suturing the deep muscular layers to maintain the 3-dimensional facial contour. Moreover, in this cadaver study, we attempt to predict the functional consequences on the impairment of facial mimics related to the Le Fort I incision.