Age and sex-related distribution of alpha angles and the prevalence of the cam morphology of the hip in Asians do not differ from those of other ethnicities

Purpose: This study was performed to evaluate the effects of age on the alpha angle and the incidence of asymptomatic cam morphology. Methods: The radiographs of asymptomatic individuals between ages 8 and 22 were retrospectively collected. A total of 1417 individuals were included and grouped according to age: 8–12 (Group A), 13–18 (Group B), and 19–22 (Group C) years. Radiographic measurements of the alpha angles of the right hip were obtained from anteroposterior (AP) and frog-leg lateral (FL) radiographs. The correlations among alpha angles, the presence of cam morphology, and age were determined. Results: The mean alpha angles of the three groups were statistically different (p < 0.001, each). The alpha angles on both radiographs were positively correlated with age. Intra-group analysis revealed that this correlation was only evident on the FL images of males in Group B. The presence of a radiographic cam morphology also positively correlated with age (p < 0.001 in both AP and FL images). The cam morphology on AP radiographs was 0 in Group A, 17(3.0%) in Group B, and 21(4.8%) in Group C; that on FL radiographs was 2(0.3%) in Group A, 45(7.9%) in Group B, and 103(23.6%) in Group C. Intra-group analysis revealed that the correlation was only significant in males in Group B. Conclusions: Higher alpha angles and the presence of cam morphology were positively correlated with age, particularly in males at or before the time of skeletal maturation. The prevalence of cam morphology did not differ from those in other ethnicities. Level of evidence: IV.