Relationships among ages at attaining 17 or 21 indices of maturity were considered in a longitudinal sample of 177 Polish boys examined at annual intervals from 1961 to 1972. Maturity indicators included ages at peak velocity for stature, sitting height, leg length and weight; ages at attaining 80%, 90%, 95% and 99% of adult stature; ages at attaining the median skeletal maturity scores (TW-2) characteristic of chronological ages 11, 12, 13, 14, and 15 years; and ages at attaining stages II and IV of genital and public hair development. Age at initiation of the stature spurt (take-off) and ages at eruption of 14, 20 and 26 permanent teeth were ascertained for only 111 boys. All intercorrelations among the developmental indicators were positive. Ordering the correlation matrix gave three clusters: (1) a large central group including age at take-off and ages at all peak velocities, at genital and pubic hair stages II and IV, at attaining 90%, 95% and 99% of adult stature, and at the later stages of skeletal maturity; (2) indices of the tempo of maturation during prepubertal and/or early pubertal stages; and (3) ages at attaining a given number of permanent teeth. Results of a principal components analysis of the ages indicated two principal components, the first accounting for about 77% of the sample variance and the second for about 12%. The first principal component is apparently a general maturity factor, while the second apparently relates to the rate of skeletal maturity during pre-adolescence.
A longitudinal sample of girls (N = 271), all born during the same year, were examined at yearly intervals during a period of 11 (N = 174) or 8 years (N = 97). The data gathered included the following: age at menarche, anthropometric dimensions, skeletal maturity scores with the TW2 method, and questionnaire information about the present and past socioeconomic situation and family dynamics. The girls were divided into two groups. Group A (N = 207) comprised girls who lived in families free of strong traumatic events. Group B (N = 64) included girls whose family dysfunction exposed them to prolonged distress. Two anthropometric dimensions were central to the analysis: height and subischial leg length. Age at attaining four different maturity stages were also used: age at menarche, age at a Carpal score of 1,000, age at the RUS score of 1,000, and age at the total bone score of 995. The mean age at menarche of girls from group A was 13.3 years and that for girls in group B was 12.9 (F = 6.295, P < 0.01). There was no correlation between age and height at final stages of skeletal maturation, i.e., at a total bone score of 995 or a RUS score of 1,000 in group A. There was no significant difference in height between girls whose skeletal maturity was completed early and those in whom it was completed late. Girls from group B, whose skeletal maturity was reached earlier, were shorter than those who grew until a later age. In group B, the stature was positively correlated with the age at which the late stages of skeletal maturation was attained (r = 0.26 at a RUS score of 1,000 and r = 0.28 at a total bone score of 995, P < 0.05). Regardless of the ages at which any of the four maturity levels were reached by girls from group A, they were, on average, taller than those from group B at the same maturity level. Only at a RUS score of 1,000, when the sample size is reduced, the difference was not significant. The results show that girls exposed to familial distress are more likely to have an early puberty, which is associated with short final stature.
In 191 Polish boys of the Wroclaw Growth Study, the relationship between skeletal age and chronological age was examined at the onset of the adolescent growth spurt (take-off) and at peak velocity of height growth (PHV). It was found that, at PHV, skeletal age is markedly less variable than is chronological age, but at take-off no such reduction in variability is visible. The following interpretation of this finding is proposed. The onset of the spurt depends, ultimately, upon some maturational processes going on in the hypothalamus and shows little relationship with the advancement of the long bones at that time. Therefore, the spurt can begin at any level of skeletal maturity within the range normally observed at the chronological age at which it happens to begin in the individual. Peak height velocity, on the other hand, is reached when skeletal maturity is sufficiently advanced for testosterone to change its influence upon the bones from one which consists in stimulating cartilage growth to one which consists in stimulating epiphyseal fusion. Therefore, PHV is bound to occur within a range of skeletal maturity much more restricted than that within which take-off can occur.
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