Background: The vector of superficial musculoaponeurotic system (SMAS) redraping in rhytidectomy is often described in relation to the zygomaticus major muscle (ZMM), so that suspension prevents distortion of the mimetic musculature and a "facelifted appearance." There are no data describing the true orientation of this muscle in the midface.
Objectives: The aim of this study was to define the vector of the ZMM relative to the Frankfort horizontal plane.
Methods: One hundred patients underwent deep plane rhytidectomy. As part of this procedure the tissues overlying the ZMM are elevated, allowing muscle orientation to be measured as an angle relative to the Frankfort horizontal plane.
Results: Data for 200 hemifaces were aggregated. The average ZMM angle was 59° (standard deviation, 6°; range, 41-72°) relative to the Frankfort horizontal plane, and showed a statistically significant pattern of change with advancing age, becoming more acute with increasing age below the age of 60 years and more obtuse with age over 60 years.
Conclusions: The native vector of the ZMM varies significantly between rhytidectomy patients as demonstrated by the high variance in this cohort. Assumptions about its orientation should not be made in rhytidectomy techniques that do not identify its course. Standard vectors of SMAS redraping, such as superior-lateral, vertically oblique, and purely vertical, should be reconsidered and a customized vector implemented in each case. Aging affects the orientation of the muscle, which can potentially be explained by soft tissue and bony changes at its attachments. This furthers the variability of the SMAS vector in each individual case.
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