Structural continuity of the perinasal-labial muscular complex: implications for Le Fort I osteotomy.

Postoperative nasal changes after Le Fort I osteotomy are common but incompletely explained. Inconsistencies in the anatomical descriptions of the depressor septi nasi (DSN), incisivus labii superioris (ILS) and nasalis may contribute to this uncertainty. This study investigated the structural continuity of the perinasal-labial musculature using gross and histological analysis. Thirty-eight sides from 19 formalin-fixed adult cadaveric heads were examined. Thirteen heads underwent gross dissection using bidirectional flip-flap and inside-out techniques to preserve muscular continuity. Six heads were processed for sagittal and axial histological sections. The relationships among the orbicularis oris (OOr), ILS, DSN, and nasalis were analyzed. The perinasal-labial musculature demonstrated continuous, multilayered architecture rather than discrete muscular units. The superior portion of the OOr extended toward the medial crus and dermis of the philtrum without direct septal cartilage insertion. The ILS originated from the anterior maxilla and was divided into inferior fibers blending with the OOr and superior fibers corresponding to the alar and transverse nasalis. No distinct borders were observed among these components. The DSN, ILS, and nasalis form a structurally continuous incisive muscle-OOr complex. Recognition of this continuity refines anatomical understanding and may clarify the morphological basis of nasal changes after Le Fort I osteotomy.