Lower digit length ratio and aggression in adolescents and young adults with boxer's fracture: A case-control study

Recent evidence shows that a lower second-to-fourth digit ratio (2D:4D), which is a sexually dimorphic trait and the indicator of prenatal testosterone exposure, may be associated with aggressive behaviors. In this cross-sectional, case-control study, we investigated: (1) Are the aggression and impulsivity levels and emotional problems higher? (2) Is the 2D:4D ratio lower in adolescents and young adults who presented with a fifth metacarpal neck fracture (boxer's fracture) compared to controls? (3) Is the digit ratio correlated with aggressive measures in individuals with a fifth metacarpal neck fracture? Seventy-one consecutive patients presented with a fifth metacarpal neck fracture within the age range of 11–25 years old comprised the study group. The control group consisted of 71 age and sex-matched subjects without a history of aggression-related injury. The aggression, impulsiveness, and psychosocial well-being were measured by self-reported questionnaires. 2D:4D was measured by conventional radiography. The 2D:4D ratio was similar between groups, however, when the analyses were conducted separately for sex, females in the study group showed lower 2D:4D than females in the control group (p = 0.001). The aggression level of the study group, measured by the Buss–Perry Aggression Questionnaire was higher than the control group (p = 0.014). The impulsiveness scores on the Barratt Impulsiveness Scale-11 were similar (p = 0.60) and the total difficulty score on the Strengths and Difficulties Questionnaire was higher in the study group (p = 0.009). A lower 2D:4D ratio significantly predicted verbal and total aggression scores (p = 0.036, p = 0.032, respectively). Our findings suggest that females with a history of aggression-related injury have lower 2D:4D, and a lower 2D:4D is correlated with higher aggression levels in both sexes. Understanding and addressing aggression in these patients may help prevent further self-inflicted injuries.