Computerized morphometric quantitation of elastin and collagen in SMAS andfacial skin and the possible role of fat cells in SMAS viscoelastic properties

Recently, the superficial musculoaponeurotic system (SMAS) was found to be a composite tissue comprising collagen, elastic fibers, and fat cells in an extracellular viscous matrix. Both SMAS and facial skin tissues exhibit vi scoelastic properties, but SMAS tissue has delayed stress relaxation. As a consequence, SMAS is viewed as a firmer elastic foundation for the more vis cous facial skin. In some patients, a slackening effect of SMAS tissue take s place over a period ranging from weeks to months after tightening. To det ermine the relative quantity of viscoelastic components and better understa nd their biomechanical behavior, a quantitative morphometric study of the e lastic and collagen fibers in the SMAS and facial skin was conducted. Thirty-four SMAS preparations were taken from 17 patients during either pri mary face lift operations (12 women) or reoperative face lift procedures (4 women, 1 man), which were performed 4 to 9 months after the original surge ry, to examine the elastin and collagen content. For comparison, preauricul ar skin was also gathered from these patients. The specimens were stained w ith Weigert's staining to identify elastin and collagen fibers. Using a com puterized morphometric analysis, 100 fields of each SMAS and skin specimen were examined. According to our findings, the average percentage of elastin and collagen f ibers in SMAS and facial skin was as follows: (1) the percentage of elastin fibers in the SMAS was 4.71 +/- 1.2 (standard error of mean +/- 0.0291); ( 2) the percentage of elastin fibers in the skin was 6.1 +/- 1.8 (standard e rror of mean +/- 0.0436); (3) The percentage of collagen fibers in the SMAS was 38.7 +/- 5.9 (standard error of mean +/- 0.1430); and (4) the percenta ge of collagen fibers in the skin was 48.47 +/- 6.96 (standard error of mea n +/- 0.1688). A statistical significance of p < 0.0001 was demonstrated be tween the collagen and elastin groups. A different percentage of elastin and collagen fibers was found among the 1 7 patients and within each of them separately. Neither gender nor age diffe rences were found regarding elastin and collagen fiber content. No statisti cal differences were demonstrated between specimen sources, i.e., whether t he operations were primary or reoperative face lift procedures. Findings from previous studies indicate that the cheek has two viscoelastic layers, the skin and the SMAS. The proportional similarity in average perc entages of elastin and collagen in SMAS and facial skin cannot explain the relatively delayed stress relaxation effect of the SMAS. Therefore, the fat cells that are found exclusively in the SMAS probably lend a certain degre e of firmness to this layer and play a significant role in the long-term ef ficacy of SMAS surgery.