The risorius muscle: Anatomic considerations with reference to botulinum neurotoxin injection for masseteric hypertrophy

Jung Hee Bae, Da Yae Choi, Jae Gi Lee, Kyle K. Seo, Tanvaa Tansatit, Hee Jin Kim

Research output: Contribution to journalArticle

12 Citations (Scopus)


BACKGROUND: The botulinum neurotoxin Type A (BTX) injection into the masseter muscle often causes a change in the facial expression. There is as yet no precise anatomic evidence to support this etiologic factor of constrained facial expressions. OBJECTIVE: The aim of this study was to clarify the location and boundaries of the risorius muscle and its topographical relationship with the surrounding structures. MATERIALS AND METHODS: This study involved the dissection of 48 hemifaces. The locations of origin and insertion points of the risorius muscle were measured, and the masseter muscle was divided into 6 equally sized rectangular areas. RESULTS: Cases where the masseter muscle was covered by the risorius muscle were classified into the following 4 types: in Type A, Area III was partially covered by the risorius (17.8%); in Type B, Area VI was partially covered (20.0%); in Type C, Areas III and VI were partially covered (53.3%); and in Type D, Areas II, III, and VI were covered (6.7%). CONCLUSION: These findings suggest that the medial part of the masseter muscle represents a hazard zone into which the injection of BTX may affect the risorius muscle, potentially resulting in iatrogenic unnatural facial expressions.

Original languageEnglish
Pages (from-to)1334-1339
Number of pages6
JournalDermatologic Surgery
Issue number12
Publication statusPublished - 2014 Dec 11


All Science Journal Classification (ASJC) codes

  • Surgery
  • Dermatology

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