Anti-wrinkles evaluation using the knee as area of investigation for age dependent wrinkles

11 February 2016

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, from from Dermapro and Kyung Hee University- Korea,

Skin Reasearch & Technology: complete information



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.


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.


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 (< 0.001). Also, skin elastic parameters (R2, R5, R6, R7, and Q1) showed a significant negative correlation with age on the knee (< 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 (< 0.001). In addition, all the skin aging parameters on the knee were significantly correlated with Crow’s feet (< 0.01). Skin aging on the knee had the same tendency as the Crow’s feet.


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.

Skin aging research has generally been conducted with comparison between the buttock, unexposed to the UV (ultraviolet) light, and around the eyes for the research on intrinsic and extrinsic aging representing photo-aging. Wrinkles occur by the change and decline in collagen and elastin in the dermis. This is because of decreased protein synthesis affecting types I and III collagen in the dermis with an increased breakdown of extracellular matrix proteins [1-3].

Crow’s feet, especially, are the most typical parts to observe the facial wrinkles. In addition to Crow’s feet, research on wrinkles has recently been expanded to around the mouth and on the forehead, the neck, the back of the hand, the forearm, and so forth. It is generally known that skin aging on the body occurs earlier than in the face, yet there is only a few research on aging of the knee that is prone to wrinkle due to a relatively high frequency of the UV light exposure and the movement of joints and muscles.

From the aspect of differences between the facial and the body skin, the differences are observed in the skin thickness, sensitivity to stimulation, subcutaneous fat, and the sebaceous gland distribution. In the facial skin, the skin layer is thin, the skin is high in sensitivity to external stimuli, the fat layer is not thick, and sebaceous glands are evenly distributed while the body skin is thick and less sensitive to external stimuli compared to the facial skin, the fat layer is thick and sebaceous glands are less distributed. Because of such differences, oil and moisture on the face are balanced by the sweat glands and the sebaceous glands whereas the body skin is drier compared to the facial skin.

The body skin changes by aging to become flaccid due to skin dryness and decline in elasticity resulting in a flaccid body shape, and a lot of cellulite is also observed. The breasts become flaccid and wrinkles form on the neck, hands, feet, and knees. Such changes enable to surmise the approximate age of a middle-aged woman, who has well managed her skin so that her exact age is hard to presume, by looking at her hands and feet. The knees, in particular, are functionally important and structurally unique for bending. Because the skin on the knees is crinkly and flaccid, if elasticity slightly decreases, it turns to fat and wrinkles on the knees contributing to ruin the body shape. The knees are also the body part that aging occurs earlier than other body parts because friction usually occurs frequently, and it easily becomes stiff and hard due to the thin fascia and is always dry due to very little sebum secretion.

Therefore, in this research, 38 of female subjects (age of 20s: eighteen subjects in the young group, ≥50s: 20 subjects in the old group) were selected and the degree of aging around the eyes and the knees was measured to propose objective parameters.

Materials and Methods


The study was conducted in accordance with the intent and purpose of good clinical practice regulations as described in Korean Good Clinical Practice (KGCP) and/or the Declaration of Helsinki, as appropriate. All participants provided written informed consent before their study participation commenced. All procedures for recruitment, selection, and inclusion of subjects in this study were established to provide the participants with clear and precise information, allowing them to appreciate the aims of the project and the consequences of their consent.

A total of 38 healthy Korea females (young group: 18, old group: 20) aged 20–71(average 40.53 ± 17.60) years were enrolled in this study.

Study design

This study was performed under a given relative temperature and humidity. The ambient temperature was maintained at 22 ± 2°C and the relative humidity in the range of 50 ± 5%.

Wrinkle severity grading criteria was established (grade 0~7), and then photography, visual assessment, skin wrinkle, and skin elasticity were evaluated on the knee. Body composition was measured to eliminate body fat influence. In addition, visual assessment and biophysical parameters were measured on Crow’s feet to confirm the correlation of the skin aging between facial and body skin.

Visual assessment

Digital image of knee was taken by standardized illumination. Participants were standing on with given markings at the bottom in a reproducible position. A light ring was located below the knee, so that skin wrinkles were visible as a shadow. Images were taken using Nikon D90 (Nikon, Japan). Also, the facial image photographed their lateral faces using VISIA® CR (Canfield, OH, USA).

Standard photograph of wrinkle severity on knee was established (Fig. 1). Visual assessment was independently performed by two trained researchers. The mean value was analyzed after verification of the coincidence.


Figure 1. Skin wrinkle severity scale on the knee (grade 0; no wrinkle ~ grade 7; severe wrinkle).

Instrument measurements

Body composition

Body composition for each subject was measured using Inbody® 330 (Biospace, Seoul, Korea). To eliminate body fat influence on wrinkles, body fat mass (BFM: kg), and body mass index (BMI: kg/m2) were selected for the analysis.

Skin wrinkle

Skin wrinkles on knee and crow’s feet were measured using PRIMOSshape (GFMesstechnik GmbH, Teltow, Germany) that the optical 3D capturing device was for applications that 130 × 80 × 50 mm field of view and PRIMOSpremium, that is, 24 × 14 × 13 mm field of view, respectively.

Three-dimensional image was taken and analyzed skin wrinkle parameters in terms of R-parameters (Ra, Rmax, Rz, Rp and Rv).

Skin elasticity

Skin elasticity was measured using Cutometer® MPA580 (C+K, Cologne, Germany) on knee and crow’s feet.

The device generates negative pressure, 450 mbar. Skin is drawn into the aperture of the probe with constant negative pressure for 1 s (on-time). Afterward, the negative pressure is switched off for 1 s and the skin returns to its original shape (off-time). It is set ten repetitions in one measuring cycle.

Statistical analysis

All statistical analyses were performed by using spss Package Program 11.5 (SPSS Inc., Chicago, IL, USA). Independent t-test was carried out to confirm homogeneity and to compare the two groups. Intraclass Correlation Coefficient (ICC) was used to analyze verification of the coincidence between two researchers. In addition, we used Pearson’s Correlation Coefficient to see whether data are statistically correlated with age and measurement sites. A P-value of < 0.05 was considered statistically significant.



In this research, we applied a new evaluation method of wrinkle and elasticity on the knee. Wrinkles on the face are the most certain marker of aging. Most of the published studies are about wrinkles in specific locations on the face, such as Crow’s feet, forehead [4, 5], nasolabial fold, and glabellar lines [6], and lip [7, 8]. Crow’s feet, especially, is the most representative site to evaluate wrinkles. In recent studies, Alex Nkengne et al. [9] explained that skin aging indexes are highly correlated with the real and the perceived facial skin age. Y. Masuda et al. [10] discussed skin surface micro-topography as an effective tool to characterize the condition of the skin on cheek. Also, Stefanie Luebberding et al. [11] showed Crow’s feet and forehead lines are pronounced first, whereas glabella lines develop in mid-forties using three-dimensional digital fringe projection method, and wrinkle severity increases at all locations every 10 years of age. Likewise, various wrinkle studies are performed but still only limited sites have been studied. Skin wrinkles on body sites are very rarely known.

Therefore, we determined if the knee was a representative site on the body because the knee is a site in which muscle movement and UV exposure are considered for other body sites. First, wrinkle severity criteria on the knee were established using gray scale digital image. Then, visual assessment, skin wrinkle, and skin elasticity were measured. In addition, BMI and BFM were related to skin elasticity in our pretest (Data not shown). We tested homogeneity of BMI and BFM between groups to control body fat influence. Skin aging parameters were compared with age- and site-dependents.

As a result of visual assessment on the knee, there was a significant positive correlation with age and significant difference between two groups (< 0.001). Also, skin wrinkle parameters were significantly low, and skin elastic parameters were significantly high in the young group (< 0.001). The younger group had less wrinkles and higher elasticity on the knee. Also, visual assessment was highly correlated with skin wrinkle and elasticity parameters.

To confirm how much two different sites that are on face and body were related, biophysical properties were compared between Crow’s feet and the knee. All the parameters on the knee were highly related to Crow’s feet. Therefore, there was the same tendency of aging between Crow’s feet and the knee.

This study has shown the new wrinkle severity criteria on knee. Visual scoring, skin wrinkle, and elasticity might be useful for evaluation of aging not only on the facial sites but also on the body sites. Also, the knee is considered that it could be a suitable for observing body aging. This study would be a starting point to research body aging. Furthermore, we will continue to study other sites of the body to compare which site is the most visible for aging. In addition, other biophysical properties of body aging will be evaluated

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