The Deep-Plane Transition Zone: A Key Anatomic Consideration In SMAS Lifting of the Midface (*previously presented at ISAPS regional course, St. Petersburg, Russia, June 5, 2011)

Goals/Purpose:

Recent anatomic studies suggest that the SMAS attenuates as it courses over the zygomaticus major muscle to enter the midface.  Hence, at the SMAS level of dissection, there are no durable, surgically useable connections between the SMAS laterally and midfacial structures such as the malar fat pad; instead, the only durable connection is the skin, used as a “cantilever.”  Thus, in order for SMAS lifting to exploit this connection and translate into the midface, the skin and SMAS must be left as one layer in a two-centimeter (or greater) width zone lateral to zygomaticus major muscle.  I term this the “Deep-plane Transition Zone” (DTZ).  This is standard with the deep-plane technique, since skin and SMAS remain as one layer throughout the lateral dissection.  However, as long as the skin-SMAS attachments are maintained in the DTZ (and zygomatic and parotid-masseteric ligaments are adequately released), midface elevation is possible with bilamellar SMAS imbrication techniques as well.  This paper tests this concept by comparing a group of facelifts done with skin and SMAS separated in the DTZ with a latter group in which they were left attached.

Methods/Technique:

Between January 2008 and December 2010, 24 patients (22 women and 2 men) underwent SMAS facelift (deep-plane or bilamellar) with specific need for midface elevation, and without concomitant fat grafting, maintaining the skin and SMAS as one layer in the DTZ.  Midfacial elevation was measured by digitally determining the percentage decrease in the distance from the lower lid margin to the lid/cheek junction on preoperative and postoperative frontal photographs matched exactly for size and orientation.  Forty-eight hemi-midfaces were compared.  The same analysis was done for 48 hemi-midfaces (24 patients, same sex ratio, same exclusion criteria) undergoing a similar procedure between January 2006 and December 2007, with skin and SMAS separated in the DTZ. 

Results/Complications:

In the group prior to maintenance of the DTZ, the mean percentage of mid-facial elevation at six months postoperative was 4.82%.  In the subsequent group, the mean percentage of mid-facial elevation at six months postoperative was 10.72%.  Complications were minimal, with no hematomas and no facial nerve injuries. 

Conclusion:

Maintaining skin and SMAS as one flap in the Deep-plane Transition Zone improves midface elevation during SMAS facelifting.

FIGURE 1.  The Deep-Plane Transition Zone (DTZ), in red

FIGURE 2.  The Deep-Plane Transition Zone shown with color-coded limits of skin and SMAS undermining.  Note that either a Deep-Plane or Bilamellar technique can be used and still respect the skin-SMAS ligamentous attachments in the DTZ.

FIGURE 3.  SKIN AND SMAS SEPARATED IN DTZ - SMAS traction has no effect on malar fat pad

FIGURE 4.  SKIN AND SMAS TOGETHER IN DTZ - SMAS traction lifts malar fat pad

FIGURE 5.  BEFORE (LEFT) AND AFTER (RIGHT) PHOTOS OF PATIENT WITH SKIN AND SMAS TOGETHER IN DTZ

 

FIGURE 6.  HALF-AND-HALF PHOTOGRAPH CONTRASTING THE SAME HEMI-MIDFACE BEFORE AND AFTER, SHOWING LOWER-LID MEASURING TECHNIQUE