Direct muscular connection between the orbicularis oculi and risorius muscles: a case report.

[PURPOSE] The orbicularis oculi (OOc) and risorius muscles are typically regarded as distinct anatomic and functional units with no known direct muscular connections. Although rare variants of the facial musculature have been reported, their implications for facial dynamics and clinical practice remain underexplored. To the best of our knowledge, this report presents a previously undescribed direct link between the OOc and risorius muscles, highlighting their potential functional and clinical significance.

[METHODS] This report presents an anatomical variant in which the lateral fibers of the OOc muscle descend abnormally, running lateral to the zygomaticus major and in close proximity to the zygomatic retaining ligaments (McGregor's patch).

[RESULTS] In the mid-cheek region, several of these fibers blended with the superior fibers of the risorius muscle, forming a direct muscular connection at the lateral boundary of the facial expression muscles, and ultimately inserting into the modiolus. This bilateral anatomical variant was not accompanied by other notable anomalies in the adjacent facial structures.

[CONCLUSION] This report presents a previously undescribed direct connection between the OOc and risorius muscles. This configuration may allow for coordinated movement between eyelid closure and mouth corner retraction, thereby facilitating complex and integrated facial expressions. Clinically, recognition of this variation is important for procedures such as botulinum toxin injection, musculo-aponeurotic system-based facial surgery, and facial reconstruction, as it may influence both functional and aesthetic outcomes.