How much related to skin wrinkles between facial and body site? Age‐related changes in skin wrinkle on the knee assessed by skin bioengineering techniques

Background/purpose Skin aging has been focused the wrinkle on the face than on the body, so most studies have been studied the change in Crow's feet for ages. Only little is known about the age‐dependent changes of wrinkles on body sites. The aim of this study was to establish new grading criteria for severity of wrinkles on knees and to investigate the relationship of wrinkle severity with age‐ and site‐dependent. Methods The skin on the knee of 38 healthy Korean female volunteers, divided into two groups young and old, were photographed. Standard photograph for body wrinkle was established (grade 0~7), and then visual assessment, skin wrinkle, and skin elasticity were evaluated on Crow's feet and the knee. We examined for any significant differences and the correlation of skin aging parameters with age and two different sites. Results Skin wrinkle severity with standard photograph and wrinkle parameters (Ra, Rmax, Rz, and Rv) had a significantly positive correlation with age‐dependent on the knee ( P < 0.001). Also, skin elastic parameters (R2, R5, R6, R7, and Q1) showed a significant negative correlation with age on the knee ( P < 0.001). Skin wrinkle severity with standard photograph was highly correlated with all skin wrinkle parameters and skin elastic parameters (R2, R5, R7, and Q1) on the knee ( P < 0.001). In addition, all the skin aging parameters on the knee were significantly correlated with Crow's feet ( P < 0.01). Skin aging on the knee had the same tendency as the Crow's feet. Conclusions This study has shown the new grading criteria of wrinkles on the knee. Skin wrinkle and elasticity on the knee are age‐dependent related and aging on the knee is highly related to Crow's feet. Those parameters are using a quantitative method to evaluate body aging. Also, the knee is considered that it could be a suitable site to evaluate body aging.