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COMPARING DIGITAL THUMB AND THUMBNAIL MEASUREMENTS BETWEEN LEFT AND RIGHT HANDS

Abstract

Within traditional Chinese medicine, as well as the popular Chinese culture, it is believed that the size of the thumbnail’s lunula (whitish, half-moon shaped portion of the nail) is linked to markers of health status or physical fitness. To investigate this issue, a pilot study by our lab is collecting measures of health, wellness, and fitness in adults along with photographs of both left and right hands. Measures of lunula and nail size are being determined with standard 2D digitizing techniques, but it is not known whether measures from both left and right hands are needed or not. PURPOSE: To compare digital thumb and thumbnail measurements for the left and right thumbs. METHODS: 11 young healthy adults (10 Men, 1 Women; Mean±SD: 18±3 yrs; 22.6±2.5 kg/m2 BMI), each of whom were free of visible nail diseases, had the dorsal surface of both hands photographed with a digital handheld camera with the hands lying flat on top of a ruler. Each high-resolution image was then zoomed and cropped to focus on just the thumb and underlying ruler for each hand. The edited images were then uploaded to a computer-based digital imaging software. Prior to analysis, each image was calibrated to determine pixels/cm using the ruler within the image. Next, the measurements of lunula area (LA), nail area (NA), widest thumb width (TW), and thumb area (TA) were hand digitized. Each measure was performed three times with the average used for all subsequent analyses. These average measures (LA, NA, TW, TA) were then each analyzed using a 2-factor RM ANOVA, as well as correlations between left and right thumb measures (alpha = 0.05). RESULTS: There were no significant differences between left and right thumb measures for any variable: LA (Left: 0.28±0.10 cm2, Right: 0.27±0.09 cm2, p=0.48), NA (Left: 1.7±0.26 cm2, Right: 1.7±0.21 cm2, p=0.60), TW (Left: 2.4±0.20 cm, Right: 2.5±0.16 cm, p=0.15) and TA (Left: 5.4±1.1 cm2, Right: 5.4±0.9 cm2, p=0.62). Correlations between left and right thumb measures for LA (r=0.81), NA (r=0.96), TW (r=0.93) and TA (r=0.95) were all high (r>0.80) and significant (p<0.001). CONCLUSION: The 2D thumb and thumbnail measures were statistically identical between hands. Thus, it may not be necessary to determine 2D thumbnail measurements for both hands for the larger study in progress, and especially for healthy adults that are free of nail diseases.

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