Zygomaticus Minor Muscle

Introduction

The zygomaticus minor muscleview_in_ar is a slender muscle of facial expression located in the midface. It is classified as one of the muscles of the upper lipview_in_ar group, contributing to the complex movements involved in forming expressions. As part of the superficial musculoaponeurotic system (SMAS), it lies superior and medial to the more prominent zygomaticus major muscleview_in_ar ¹. Its primary action is to elevate the superolateral portion of the upper lipview_in_ar. The zygomaticus minor is notably one of the most variable muscles in the human body, being absent in a significant percentage of the population, a factor that contributes to individual differences in smile dynamics and facial appearance ^{1, 2}.

Anatomy

The zygomaticus minor muscle originates from the lateral surface of the zygomatic boneview_in_ar, just posterior to the zygomaticomaxillary suture and medial to the origin of the zygomaticus major muscle.view_in_ar From its bony origin, the muscle fascicles travel in an inferior and medial direction, superficial to the levator anguli orisview_in_ar muscle. It inserts into the musculature and skin of the upper lipview_in_ar, blending with the fibers of the orbicularis oris muscleview_in_ar superior to the oral commissureview_in_ar and medial to the insertion of the zygomaticus majorview_in_ar ¹. The neurovascular supply to the zygomaticus minor is consistent with other midfacial muscles. Motor innervation is provided by the zygomatic and buccal branches of the facial nerve (CN VII)view_in_ar ¹. Its arterial blood supply is derived from branches of the facial arteryview_in_ar, while venous drainage is accomplished via the facial veinview_in_ar. Anatomical variation is a hallmark of the zygomaticus minorview_in_ar. Studies have reported its absence, either unilaterally or bilaterally, in up to 36.7% of individuals ². When present, it may be bifid or show variations in its insertion point, sometimes blending with the levator labii superiorisview_in_ar ^{1, 2}.

Function

The primary function of the zygomaticus minor muscleview_in_ar is the elevation and eversion of the upper lipview_in_ar. Acting in concert with the zygomaticus majorview_in_ar and levator labii superiorisview_in_ar, it helps to expose the maxillary teeth during smiling and speaking. Its contraction pulls the upper lipview_in_ar superolaterally, contributing to the formation of a smile and expressions of happiness. Additionally, the pull of the zygomaticus minor deepens the nasolabial fold, the crease extending from the ala of the nose to the corner of the mouth, which becomes more prominent during smiling or sneering ¹. The subtle action of this muscle adds nuance to a wide range of facial expressions, including sadness, contempt, and disgust, depending on its synergistic or antagonistic action with other perioral muscles ¹.

Clinical Relevance

The zygomaticus minor muscleview_in_ar holds significant clinical importance in several medical and surgical contexts. In cases of facial nerveview_in_ar palsy, such as Bell's palsy or injury to the zygomatic or buccal branches of the facial nerveview_in_ar, paralysis of this muscle contributes to drooping of the upper lipview_in_ar and facial asymmetry, which is especially evident during attempts to smile ¹. This can lead to functional deficits, including difficulty with clear articulation and retaining food in the oral vestibuleview_in_ar. In the field of aesthetic medicine, hyperactivity of the zygomaticus minor, along with the levator labii superiorisview_in_ar and levator labii superioris alaeque nasiview_in_ar, can cause excessive gingival display, or a "gummy smile." This condition is often treated with targeted injections of botulinum toxin type A to weaken the muscles and reduce the degree of upper lipview_in_ar elevation. For surgeons, knowledge of the zygomaticus minor's anatomy and its frequent variations is crucial during facial rejuvenation procedures like facelifts (rhytidectomy) and in complex facial reanimation surgeries for patients with long-standing paralysis, where it serves as a landmark or a potential target for functional restoration ².