Accuracy of scoring of the epiphyses at the knee joint (SKJ) for assessing legal adult age of 18 years

Important aspects of forensic practice are age estimation and discrimination of individuals of unknown age as adults and minors. The developing knee joint was recognized as a potential site for age examination in late adolescence. We analyzed a sample of anteroposterior x-rays of the knee joints from 446 living individuals from Umbria, Italy (234 males and 212 females), aged between 12 and 26 years. We evaluated the ossification of the distal femoral (DF), proximal tibial (PT), and proximal fibular (PF) epiphyses. We took into account possible persistence of the epiphyseal scars in the ossified epiphyses by the adopted stages of those previously introduced by Cameriere et al. (2012). We also used measurements from all three epiphyses to calculate the total score of maturation for the knee joint (SKJ). Cohen Kappa coefficients of intrarater agreement for staging the DF, PT, and PF epiphyses were 0.839, 0.894, and 0.907, while interrater agreement was 0.919, 0.791, and 0.907, respectively. The resulting receiver operating characteristic (ROC) curves of SKJ show better discriminatory power than those for DF, PT, and PF epiphyses in predicting that the participant, either male or female, was an adult or a minor. The areas under the curves for SKJ were 0.991 and 0.968 vs. 0.944, 0.962, 0.974 and 0.891, 0.910, 0.918 for males and females, respectively. The results of the 2 by 2 contingency tables showed that SKJ score of 4 in males and SKJ score of 5 in females were the most suitable cut-off value in discriminating between adults and minors. Principally, the sensitivity test for males was 0.94, with 95 % confidence interval (95 % CI) 0.90 to 0.97 and specificity was 0.96 (95 % CI 0.91 to 0.98). The proportion of correctly classified individuals was 0.95 (95 % CI 0.91 to 0.97). For females, the sensitivity test was 0.89 (95 % CI 0.84 to 0.92) and specificity was 0.92 (95 % CI 0.87 to 0.96), the proportion of correctly classified individuals was 0.90 (95 % CI 0.85 to 0.94). These results indicate that the SKJ method may give valuable supporting information in forensic procedures for discriminating individuals of legal adult age of 18 years. Further studies should address the usefulness of the SKJ method in different populations.