RADIOGRAPHIC ABSORPTIOMETRY OF THE PHALANGES IN HEALTHY-CHILDREN AND IN GIRLS WITH TURNER SYNDROME

Although bone mineral status in children has been measured with variou s techniques, information about development of the actual bone mass de nsity during childhood and adolescent growth is scarce. Our modified r adiographic absorptiometry (RA) determines bone mass density (BMaD) th ree dimensionally at the diaphyseal and metaphyseal site of the middle phalanx of the left second digit, representing predominantly cortical (50% site) and trabecular bane compartments (25% site), respectively. The objectives of this study were to establish reference curves with 95% prediction intervals of BMaD in relation to bone age (BA) during c hildhood and adolescence (N = 303) determined by RA. The specific effe cts of female puberty on BMaD were studied comparing the values of 110 untreated girls with Turner syndrome (TS) with those of the female re ference group. For either sex, a piecewise linear model with one infle ction point (IP) was postulated for the relationship of both the 25% a nd 50% site with BA. The IPs appeared at exactly the same BA (11.5 ''y ears'') for both the 25% and 50% site in boys and for the 25% site in girls. However, in girls the 50% site IP appeared 0.25 ''years'' later . All BMaD values to the left of the IPs showed little increase with a ge. In contrast, the slopes to the right of the IPs showed in both gen ders regression coefficients of approximately 0.05 for the 25% site. F or the 50% site, the regression coefficient in girls was markedly high er (0.075) than in boys (0.058), resulting only in girls in a signific ant difference between the 25% and the 50% site to the right of the IP (p = 0.03). The 95% prediction interval for both measurements is some what larger in girls than in boys. Gender differences for the onset of the pubertal BMD increase in relation to chronological age (CA) repor ted with single and dual photon absorptiometry and dual energy X-ray a bsorptiometry could not be confirmed; however, these are subjective to changes in size and shape of bone during growth. Our data are in agre ement with quantitative computed tomography measurements. Untreated gi rls with TS, lacking spontaneous puberty, show a slight increase with BA without an IP and confirm the absent influence of puberty. Modified RA of the hand proves to be a convenient, accurate, and reproducible method to measure actual BMaD in the pediatric clinic. Since BA reflec ts biological maturation better than CA, relating the BMaD values to B A should be helpful in deciding whether or not a child has an abnormal BMaD.