Identification of age and sex based on knee radiography

The identification of age and sex constitutes the cornerstone in biological profile determination. Identification of age and sex depends mainly on ossification of bones and sexual dimorphism respectively. The knee is an ideal site for assessment of 3 epiphyseal unions at the same time. Moreover, patella is a compact bone that could display sexual dimorphic characters. A total of 479 anteroposterior and lateral radiographs of the knee were reviewed retrospectively in subjects aged between 10 and 20 years old; 255 males and 224 females. Epiphyseal union was scored as stage 0 (non-union), stage 1 (beginning union), stage 2 (active union), stage 3 (recent union) or stage 4 (complete union). Three measurements on patella (maximum height, width, and thickness) were used to determine sex by univariate and multivariate discriminant analysis. Intra- and inter-observer variability were excellent. Mean age increases with each stage of union and also varies between sexes. The relationship between the three knee epiphyses and chronological age was strong for both sexes. It has been noted that union occurs at an earlier age in the Chinese population. As expected, epiphyseal union in females occurred earlier than males. Interestingly, the present study exhibited that stage 2 of the three knee epiphyses occurs in males earlier than their female counterparts by 6 months. Compared with previous published data, the patella in this study was small and wide. The best discriminant functions for sex determination were 73% which is obtained by the combination of 2 measurements only; height/thickness and height/width. Thus, the patella is of limited value as sex indicator. Further studies on different areas within China are recommended in order to verify not only the accuracy of the used methods but also to enable evaluation of different ethnic groups. Further studies based on different anatomical regions for assessment of sex are also encouraged.