Clinical anatomic considerations of the zygomaticus minor muscle based on the morphology and insertion pattern.

BACKGROUND: The zygomaticus minor muscle (Zmi) is involved in the expression of many different facial emotions. However, the details of its insertion pattern and morphology are not well described. OBJECTIVE: The aim of this study was to clarify the morphology and insertion pattern of the Zmi, and to provide clinical anatomic information that will help elucidate its roles in animation. MATERIALS AND METHODS: Fifty-four embalmed adult hemifaces (18 men and 12 women; mean age, 67.4 years) from 30 cadavers were used in this study. The dissection was performed with the aid of a surgical microscope. RESULTS: This muscle could be classified into 3 types (A-C). Type A, in which the Zmi attached only to the upper lip, was observed in 63.0% of cases (34/54) and could be subdivided into 2 types: straight (A-1; 31.5%, 17 cases) and curved (A-2; 31.5%, 17 cases). Type B, in which the Zmi was attached to both the upper lip and the lateral alar region, occurred in 27.8% of cases (15/54). In Type C (9.2% of cases, 5/54), there was either no or only undeveloped Zmi fibers. CONCLUSION: The present finding of Zmi fibers being attached to the alar region in many cases (27.8%) suggests that this muscle is involved in elevation of both the nose ala and upper lip during various facial animations.