The normal centre-edge angle of Wiberg in the Chinese population: a population-based cross-sectional study

This study was designed to provide normal reference values for the centre-edge angle of Wiberg in the Chinese population by measuring 1494 radiographs according to the criteria of Tönnis. The mean angle was 23.1 degrees (4.7 degrees to 46.4 degrees) in childhood (four to nine years), increasing to 28.9 degrees (6 degrees to 48 degrees) in adolescence (10 to 18 years) and reaching 32.8 degrees (13.7 degrees to 58.8 degrees) in adults. The angle was positively correlated with age, increasing by a mean of 0.78 degrees annually before adulthood and by 0.070 degrees annually in adults. A relative upward tendency after middle age might contribute to degenerative changes. No gender difference was discovered. The change in the angle with age was similar to that observed in other ethnic groups, showing moderate differences in the average of individual age groups, but the ethnic differences are not sufficient to explain the variation of incidence of developmental dysplasia of the hip in different races.