The extended SMAS facelift: identifying the lateral zygomaticus major muscle border using bony anatomic landmarks

Extended superficial musculoaponeurotic system (SMAS) rhytidectomy has been advocated for improving nasolabial fold prominence. Extended subSMAS dissection requires release of the SMAS typically from the upper lateral border of the zygomaticus major muscle and continued dissection medial to this muscle. This maneuver releases the zygomatic retaining ligaments and achieves more effective mobilization and elevation of the ptotic malar soft tissues, resulting in more dramatic effacement of the nasolabial crease. Despite its presumed advantages, few reports have suggested greater risk of nerve injury with this technique compared with other limited sub-SMAS dissection techniques. Although the caudal extent of the zygomaticus muscle insertion to the modiolus of the mouth has been well delineated, the more cephalad origin has been vaguely defined. We attempted to define anatomic landmarks which could serve to more reliably identify the upper extent of the lateral zygomaticus major muscle border and more safely guide extended sub-SMAS dissections. Bilateral zygomaticus major muscles were identified in 13 cadaver heads with 4.0-power loupe magnification. Bony anatomic landmarks were identified that would predict the location of the lateral border of the zygomaticus major muscle. The upper extent of the lateral border of the zygomaticus major muscle was defined in relation to an oblique line extending from the mental protuberance to the notch defined at the most anterior-inferior aspect of the temporal fossa at the junction of the frontal process and temporal process of the zygomatic bone. The lateral border of the zygomaticus major muscle was observed 4.4 +/- 2.2 mm lateral and parallel to this line. More accurate prediction of the location of the upper extent of the lateral border of the zygomaticus major muscle using the above bony anatomic landmarks may limit nerve injury during SMAS dissections in extended SMAS rhytidectomy.