The viscoelastic properties of the SMAS and its clinical translation: Firm support for the high-SMAS rhytidectomy

Background: The superficial musculoaponeurotic system (SMAS) has inherent viscoelastic properties, although the optimal tension levels to minimize tissue relaxation have not been defined. This study evaluated the viscoelastic properties of the SMAS within the biomechanical parameters of the high-SMAS rhytidectomy. Methods: Patients (n = 30) underwent a high-SMAS face lift performed by the senior author (F.E.B.) with intraoperative tension at the superior (preauricular) and inferior (mastoid) points of SMAS fixation sequentially measured with a tensiometer. Fresh samples of lateral, preparotid SMAS were then harvested and evaluated ex vivo for bursting strength, stress relaxation, and creep. Results: The force applied to the superior, preauricular SMAS intraoperatively (7.21 ± 0.87 N) was significantly lower than that of the inferior mastoid point of fixation (9.59 ± 1.8 N) (p < 0.001). The bursting force of the SMAS was 55.7 N, with the average bursting pressure of 224.97 PSI. The in vivo force applied to the SMAS was found to be only 15 percent of its total bursting strength. The deformational load of the high-SMAS face lift caused only a 14 percent creep in the tissue ex vivo. Conclusions: The in vivo tension in a high-SMAS face lift is predictable, with the force applied to the mastoid point being significantly greater than that of the superior preauricular point. This intraoperative force is only a fraction of the tissues inherent bursting strength, contributing to the minimal stress relaxation and creep observed in this study. These biomechanical properties likely contribute to the effective and long-lasting correction of facial aging with the high-SMAS technique.