There have been several reports in the last 20 years assessing trends in the maturation of children and adolescents [3
]. Each investigation has examined cohorts of subjects to compare skeletal age and chronologic age within populations hypothesized to differ from the original cohort that comprised the basis of the Greulich and Pyle atlas. These new populations have included subjects from various countries and of differing races. Several of these investigations have focused on the “applicability” of the Greulich and Pyle atlas to the new populations of interest. These data have not yielded any uniform conclusions.
Van Rijn et al. [7
] and Groell et al. [3
] demonstrated a high correlation between skeletal age and chronological age in European cohorts of young males and females, and concluded that the Greulich and Pyle atlas was still applicable for their populations. Studies in the United States from 1993 to 2001 have reported an increased discrepancy between the chronological and skeletal age among the racially diverse populations, and have questioned the continued applicability of the atlas [4
]. The data in these previous reports vary, and the report by Loder et al. [4
] is most comparable to ours. They reported that, over childhood and adolescence, skeletal age exceeded chronological age by 0.31 years (±1.04 years) in girls and by 0.8 years (±1.13 years) in boys. Adolescent boys and girls together demonstrated a skeletal age exceeding chronological age by 0.41 years (±1.21 years). Subgroup analysis showed larger differences based on race. Our skeletal age–chronological age discrepancy was approximately double, with skeletal age exceeding chronological age by 0.8 years.
The difference between skeletal and chronological ages in our largely adolescent population is higher than the differences in most previous reports. Furthermore, 21% of our subjects had a 2-year or greater difference, a gap that clearly affects surgical and medical treatment. However, this gap should not be surprising, as patterns of maturation change over time, and Himes [8
] suggested that skeletal maturation would increase by approximately 0.22–0.66 years per decade. Based on our findings, together with other reports, the current gap between skeletal and chronological ages is on the lower end of this possible spectrum.
Despite a more rapid skeletal maturation and a variability in maturation rates based on race and other factors, there is no indication that specific bony maturation patterns have changed since the Greulich and Pyle atlas was introduced. Our data confirm that skeletal age and chronological age remain highly correlated. We believe that these data, indicating advanced skeletal age beyond chronologic age in a current cohort of American adolescents, represent a note of caution for those planning medical or surgical treatment for growth abnormalities. We still find the Greulich and Pyle atlas useful, and believe that the accurate assignment of skeletal age is more important now than ever before, as today chronological age is less likely to accurately represent remaining skeletal growth.
There are several weaknesses of this investigation. First, despite a similar number of participants to previous investigations, the number of males and females for each age group is limited [5
]. Therefore, it is likely that, with an increased number of subjects, the absolute differences between skeletal age and chronologic age may have varied, but we believe the overall trends would remain similar to those identified in these 138 subjects. Second, we recognize that the gap in skeletal and chronological ages is affected by numerous factors not assessed in this manuscript, including race, socioeconomic status, and nutritional status. These are more difficult to assess and would require a dramatically larger number of subjects; furthermore, our clinic population may not be amenable to an assessment of racial disparities. Additionally, the authors note that the chronologic age of subjects was assessed in yearly increments without “rounding up” to the next advanced year. This introduces a slight discrepancy with the Greulich and Pyle method, as some years are broken into 6-month intervals. As these 6-month intervals are inconsistently included in the atlas, any uniform treatment of chronologic age would introduce some discrepancy. As our current data analysis would tend to bias toward the subjects that appear slightly more skeletally mature, we focused on and reported on those subjects of each gender in which skeletal age exceeded chronologic age by at least 2 years. Finally, in this study, a single senior reviewer evaluated skeletal age for all 138 participants. This attending physician was trained in the Greulich and Pyle method and regularly utilizes this technique; furthermore, on re-evaluation of a subgroup of the X-rays by an independent physician, similar results were found, with a high reliability confirmed. We presume that this review with a subset analysis for inter-rater reliability is sufficient given the exceptionally high previously documented inter- and intra-rater reliability of senior evaluators using the Greulich and Pyle method [4
In conclusion, this investigation demonstrated an unexpectedly high percentage of otherwise normal American adolescents born between 1989 and 1996 who demonstrate skeletal maturity exceeding chronologic age. Females between the chronologic ages of 12 and 15 are most likely to demonstrate a discrepancy of at least 2 years between skeletal and chronologic age, while males demonstrate this potential throughout adolescence.