Hand Pattern Based on Second-to-Fourth Digit Ratio: Its Relationship to Sex, Body Mass Index, and Physical Activity

BACKGROUND: The second-to-fourth digit ratio is measured by dividing the length of the index finger by the length of the ring finger. A ratio <1 means that the ring finger is longer; this is known as the male pattern or “A” pattern. A ratio >1 means that the index finger is longer; this is known as the female pattern or “C” pattern. When both fingers are equal in length (ratio = 1), the pattern is labeled as “B” pattern; this may be seen in both sexes. None of the previously reported studies on this topic were reported in the plastic or hand surgery literature. Our aim is to increase the awareness of plastic and hand surgeons to these types of hand patterns and to correlate such patterns to sex, body mass index (BMI), and physical activity in a group of healthy medical students and interns. METHODS: We conducted a cross-sectional study on 160 healthy medical students/interns. There were 82 females and 78 males between the ages of 20 and 30. A male pattern (pattern A) was defined as pattern A in both hands or pattern A in one hand and pattern B in the other hand. A female pattern (pattern C) was defined as pattern C in both hands or pattern C in one hand and pattern B in the other hand. The correlation between hand pattern and sex, BMI, and physical activity was done using the chi-square test and Fisher’s exact test. A P value of <0.05 was considered statistically significant. RESULTS: Five participants (3.1%) had pattern B in both hands. Another 15 participants (9.4%) had a male pattern in one hand and a female pattern in the other hand. Both of these groups were excluded from the statistical analysis. Pattern A was significantly higher in males, and pattern C was significantly higher in females (P < 0.001). BMI and physical activity did not significantly affect the hand pattern in males. However, the correlations between hand pattern and both BMI and physical activity were significant in females (P = 0.005 for BMI) (P = 0.042 for physical activity). CONCLUSIONS: About 12.5% of the study group did not fit into a male or female pattern. In the remaining 87.5% of the participants, sex correlated with hand pattern. BMI and physical activity significantly affected the hand pattern in females. We believe that our study will encourage plastic surgeons to further investigate the correlation of different hands patterns to other variables of interest in plastic surgery such as masculine facial anthropometric values, hypoplastic breasts, gynecomastia, and lipodystrophy.