Because of the widespread reliance on SMAS tightening procedures in present-day face lift surgery, a study was undertaken to examine the physical properties and microscopic structure of both virginal (40 specimens) and reoperated (8 specimens) SMAS tissue. The findings could be of practical value to the surgeon and are reported herewith: First, the SMAS is a composite fibrofatty layer comprising collagen and elastic fibers interspersed with fat cells. Second, microscopic appearance shows a considerable amount of elastic fibers in close relationship to the collagen fibers. Third, on scanning electron microscopy, the collagen fibers in the virginal SMAS show a convoluted appearance similar to that found in the dermis. In the reexcised SMAS tissue, there is some evidence of parallelization of the collagen fibers as seen in the stretched dermis. Fourth, mechanical testing (Instron), i.e., a series of loading/unloading tests at various rates and amplitudes, and stress relaxation tests were performed on samples of preauricular skin and SMAS. These indicated definite viscoelastic properties for both sets of specimens, with the tendency of an increased stiffness and a reduction in viscoelastic effects on repeated working of the samples. Overall, the mechanical behavior of both tissues was somewhat similar, the viscoelastic effects in SMAS being less pronounced. A nonlinear viscoelastic model is under development to represent the behavior of both tissues. The implications of these results may help to explain the slackening effect observed in some postoperative patients.

A study was undertaken to determine the physical properties and microscopic structure of the superficial musculoaponeurotic system (SMAS) tissue. Forty virginal specimens and eight reoperated specimens were examined. The following findings were discovered. 1) Microscopic appearance shows the SMAS to consist of collagen fibers, a relatively high concentration of elastic fibers interspersed with fat cells. 2) On scanning electron microscopy, the virginal SMAS shows the collagen fibers to have a similar convoluted appearance as in the dermis. There is some evidence of parallelization of the collagen fibers in the reexcised SMAS specimens. 3) Mechanical testing (Instron) demonstrates that both the SMAS and preauricular skin were subjected to a series of loading/ unloading tests at various rates, amplitudes, and stress relaxation tests. Both sets of specimens indicated definite viscoelastic properties. Although the mechanical behavior of both tissues was somewhat similar, the viscoelastic effect of the SMAS was less pronounced. A slackening effect of the SMAS indicated a gradual expansion of the SMAS postoperatively. These results could provide some indication of the long-term effects of SMAS surgery.