Conventional Techniques for Skeletal Determinations

In the evaluation of physical development in children, variations in maturation rate are poorly described by chronological age. Thus, for many decades, scientists have sought better techniques to assess the degree of development from birth to full maturity. Measures of height, weight, and body mass, although closely related to biological maturation, are not sufficiently accurate due to the wide variations in body size. Similarly, the large varia tions in dental development have prevented the use of dental age as an overall measure of maturation, and other clinically established techniques are of limited value. As examples, the age at menarche, although an important biological indicator, relates to only half the population, and determinations of sexual development using the Tanner classification, while an extremely useful clinical tool, is subjective and restricted to the adolescent period. Unfortunately, most available maturational "age" scales have specific uses and tempos that do not necessarily coincide.

Skeletal age, or bone age, the most common measure for biological maturation of the growing human, derives from the examination of successive stages of skeletal development, as viewed in hand-wrist radiographs. This technique, used by pediatricians, orthopedic surgeons, physical anthropologists and all those interested in the study of human growth, is currently the only available indicator of development that spans the entire growth period, from birth to maturity. Essentially, the degree of skeletal maturity depends on two features: growth of the area undergoing ossification, and deposition of calcium in that area. While these two traits may not keep pace with each other, nor are they always present concurrently, they follow a fairly definite pattern and time schedule, from infancy to adulthood. Through radiographs, this process provides a valuable criterion for estimating normal and abnormal growth and maturation.

Fig. 2. Comparison of the traditional Greulich and Pyle atlas used for determination of bone maturity from hand radiographs and the electronic alternative, a digital atlas of "idealized" hand radiographs that can be reviewed on standard hand-held PDAs

Greulich And Pyle Atlas

Fig. 2. Comparison of the traditional Greulich and Pyle atlas used for determination of bone maturity from hand radiographs and the electronic alternative, a digital atlas of "idealized" hand radiographs that can be reviewed on standard hand-held PDAs

Greulich and Pyle and Tanner-Whitehouse (TW2) are the most prevalently employed skeletal age techniques today [10, 11]. Despite their differing theoretical approaches, both are based on the recognition of maturity indicators, i.e., changes in the radiographic appearance of the epiphyses of tubular bones from the earliest stages of ossification until fusion with the diaphysis, or changes in flat bones until attainment of adult shape [12].

The standards established by Greulich and Pyle, undoubtedly the most popular method, consist of two series of standard plates obtained from hand-wrist radiographs of white, upper middle-class boys and girls enrolled in the Brush Foundation Growth Study from 1931 to 1942. Represented in the Greulich and Pyle atlas are 'central tendencies', which are modal levels of maturity within chronological age groups. The skeletal age assigned to each standard corresponds to the age of the children on whom the standard was based. When using the Greulich and Pyle method, the radiograph to be assessed is compared with the series of standard plates, and the age given to the standard plate that fits most closely is assigned as the skeletal age of the child. It is often convenient to interpolate between two standards to assign a suitable age to a radiograph. The apparent simplicity and speed with which a skeletal age can be assigned has made this atlas the most commonly used standard of reference for skeletal maturation worldwide.

Underlying the construction of the Greulich and Pyle atlas are the assumptions that, in healthy children, skeletal maturation is uniform, that all bones have an identical skeletal age, and that the appearance and subsequent development of body centers follow a fixed pattern. However, considerable evidence suggests that a wide range of normal variation exists in the pattern of ossification of the different bones of the hand and the wrist and that this variation is genetically determined. In fact, most standards in the atlas include bones that differ considerably in their levels of maturity [10].

Greulich and Pyle did not formally recommend any specific technique for the use of their atlas. Rather, they suggested that atlas users develop their own method depending on their preferences. Pyle et al did, however, suggest the rather cumbersome approach that each ossification center be assigned a bone-specific bone age, and the average of the ages calculated. By and large, when there is a discrepancy between the carpal bones and the distal centers, greater weight should be assigned to the distal centers because they tend to correlate better with growth potential [5].

A number of important caveats concerning bone age must be considered. First, experience in skeletal maturity determinations and a similar analytic approach are essential to enhance inter- and intra-observer reproducibility. Clinical studies and trials involving bone age as an outcome measure greatly benefit from the inclusion of experienced readers who use similar approaches in their assessments. Second, the normal rate of skeletal matura tion differs between males and females, and ethnic variability exists. Lastly, these references are not necessarily applicable to children with skeletal dysplasias, endocrine abnormalities or a variety of other causes of growth retardation.

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