Relationship of the Zygomatic Facial Nerve to the Retaining Ligaments of the Face: The SubSMAS Danger Zone

Background: Understanding the anatomy of the superficial musculoaponeurotic system (SMAS) is critical in modern facelift surgery. The transition zone between cheek SMAS and malar SMAS, is considered the most difficult portion of the SMAS to raise due to anatomic variance and proximity of zygomatic nerve branches. We attempted to further clarify the three dimensional anatomy of this area.

Methods: Facial dissection was performed on 12 fresh cadavers (24 hemifaces) using 2.5x loupes. Each hemiface was marked with vertical (y) and horizontal (x) coordinates. The zygomatic and masseteric retaining ligaments and the zygomatic and buccal facial branches in the area of dissection were identified and the depth of the nerves in the areas of interest was recorded. 95% confidence regions for the locations of the zygomaticus major (ZM) origin and the main zygomatic retaining ligament (MZRL) and upper masseteric retaining ligament (UMRL) were created.

Results: The distribution, density, and size of the retaining ligaments were variable among every hemiface. The MZRL & UMRL were located in a relatively constant locations at 44.91 mm ± 9.72 mm and 46.35 mm ± 8.34 mm from the tragus. The mean vertical distance between the MZRL and UMRL was 10.95 mm ± 4.07 mm. There was an upper zygomatic branch that invariably passed in between the MZRL and UMRL and was always located deep (mean 4.07 ± 1.29 mm) in the subSMAS plane of dissection and passed under the upper third of the ZM, [Figure 1]. This nerve penetrated zygomatic or upper masseteric retaining ligaments in only 27 percent of cases. There was an inferior zygomatic branch that passed inferior to UMRL or penetrated its inferior margin (54 percent of cases). The mean distance of this nerve from the UMRL was 1.42 ± 1.56 mm and was located more superficially (mean depth 1.41± 0.95 mm) becoming visible just distal to the ligament, [Figure 2]. The parotid gland was found to be a major factor in the variability of ligaments and nerves.

Conclusion: Despite anatomic variation, the MZRL and UMRL can be used as landmarks during dissection and they create a safe passage in between, through which a zygomatic facial branch passes deep. The area of danger is immediately inferomedial to the UMRL where a zygomatic branch becomes superficial and vulnerable.