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Advanced skeletal development in low-incomeNegro children
June, 1972 The Journal o[ P E D I A T R I C S
965
Advanced skeletal development in low-income Negro cl 'ldren The age at radiographic appearance o[ postnatal ossification centers o] 1,942 American Negro children proved to be advanced over the age at appearance in the same hand centers in 3,046 boys and girls o[ European ancestry, by approximately 0.5 standard deviations, even though the socioeconomic status o[ the Negro children was 0.6 income/ needs units lower than that o[ the Caucasian sample.
Stanley M. Garn, Ph.D.,* Sam T. Sandusky, B.A., Jerrold M. Nagy, A.B., and
Mary B. McCann, M.D., A n n Arbor, Mich., and Atlanta, Ga.
B o , z s a N D G I R L S of African ancestry tend to be advanced in postnatal ossification? ,2 Such developmental advancement has been reported from West Africa, 3 East Africa, 4 and South Africa. 5, 6 Osseous advancement was reported as early as 1925 for American Negro children, who are largely of West African ancestry, 7-~~ but with a 20 to 25 per cent accretion of European genes? ~ However, it is not clear how long and to what extent advanced ossification continues. Some of the studies have been concerned only with the neonate and with the earliest appearing h i p and hand centers J, s, 10 Others have reported a shift from comparative skeletal advancement to relative delay by the middle or the end of the first year, s by 18 months, 3 or by three years. In most studF r o m the Center for H u m a n G r o w t h a n d D e v e l o p m e n t , T h e University of M i c h i g a n , and the Center for Disease Control.
Supported by Contract HSM 110-69-22 with the Center for Disease Control, Atlanta, Ga. "~Reprint address: Center for Human Growth and Development, The Univers:ty o] Michigan 611 Church St., Ann Arbor, Mich. 48104.
ies the number of Negro children was small at each age interval, and adequate socioeconomic data have been invariably lacking. In the present comparison, we have the advantage of a rather large sample size (N 5,000), a broad sampling base--from Massachusetts to California, and socioeconomic data for the generally low-income families. The indications are that at a mean income/needs ratio near the poverty line, children of largely African ancestry are impressively advanced in the age at appearance of 25 postnatal ossification centers of the hand and wrist.
MATERIALS AND METHODS This investigation is based upon the age at appearance of 25 postnatal ossification centers of the hand and wrist as seen in the radiographs of 4,988 participants in the Multistate Nutrition S u ~ e y of 1968 to 1970. Recording the presence or absence of each postnatal ossification center on optical scanning cards, and transferring the dichotomous (present-absent) data to magnetic tape, two Vol. 80, No. 6, pp. 965-969
966
Garnet
The Journal of Pediatrics June 1972
al.
measures were computed by the I B M 360/ 67 computer. One was M, corresponding to the arithmetic mean in a Gaussian distribution. The second measure was _~, as derived from the cumulative frequency curve, 12 and mathematically defined as: 1
K~/2II with K being the average slope of the curve. Throughout the study, age (C.A.) was calculated as the exact age (using both birth date and examination date) : Subjects lacking either were excluded from the computation. The sexes were separated, as were participants of European ancestry ("Whites") and those of largely African ancestry, i.e., American Negroes or "Blacks" as currently defined. I n all there were 3,046 Whites, largely derived from Northern European ancestors, and 1,942 Blacks, largely of West African ancestral origin. 11 The limits of individual cumulative frequency curves were the earliest age at which each center was observed and the first age at which 100 per cent of radiographs evidenced the center in question. Relative income or (income/needs) was individually expressed by the Orshansky Index, a measure that takes family size and age of family members into account. 13 The participating states were Massachusetts, New York, Michigan, Kentucky, West Virginia, South Carolina, Texas, California, and Washington; the metropolitan areas of Bos~ ton, New York, Detroit, and Los Angeles were included. In expressing the percentage difference in postnatal ossification timing between Blacks and Whites, a value of 0.75 years was added to each mean age in order to avoid implausibly large percentage differences that ensue when birth age is taken as zero time. Such "conception correction" gives a more useful measure of relative timing between races and between sexes? 4 RESULTS
As shown in Table I, ossification in children of largely African ancestry occurs at an
earlier mean age than in boys and girls of European ancestral origin. Excluding the capitate, hamate, and distal epiphysis of the radius, for which comparative data were too meager, this generalization holds for both sexes, and with but one exception out of 50 race-sex comparisons. For Black boys, the conception-corrected advance in ossification timing averages 7.8 per cent; the largest relative differences are exhibited by the epiphysis of the fifth metacarpal and by the epiphyses of the distal segments of the second and fifth fingers. For Black girls, the comparable advancement in postnatal ossification timing was 18 per cent or more for six ossification centers, and averaged 12.0 per cent for all 25 centers. More usefully expressed in Z scores (i.e., standard deviation units), nine centers were advanced 0.5 S.D. or more in Black boys, and 16 postnatal ossification centers were comparably advanced in Black girls. Overall, the developmental skeletal advancement averaged half a standard deviation, i.e., +0.36 S.D. in Black boys and +0.57 S.D. in Black girls. The advancement in postnatal ossification timing in Black boys and girls was highly significant by any reasonable test, the sign test alone being 49:1 as compared with the chance or 25:25 distribution. It was, moreover, usefully large from a clinical point of view, since the difference is half a standard deviation. If there is a drop-off in relative skeletal advancement of Black boys and girls as often suggested, it is long after the third year. Within the limits of the study, i.e., the appearance of the distal epiphysis of the ulna at 5.6 to 7.2 years, Black boys and girls were still ahead of their White counterparts (Table I ) . DISCUSSION
The radiographic findings in this multistate nutritional survey, involving nearly 5,000 boys and girls, are both simple and definitive. The average age at appearance o f 25 postnatal hand-wrist centers is nearly 10 per cent ahead in children of largely African ancestry. The advancement in skeletal
Volume 80 Number 6
Skeletal d e v e l o p m e n t in low-income Negro children
96 7
T a b l e I. B l a c k - W h i t e differences in ossification t i m i n g
Black
Ossification center Proximal 3 Proximal 2 Proximal 4 Distal 1 Metacarpal Metacarpal Proximal 5 Metacarpal Middle 3 Middle 4 Middle 2 Metacarpal Distal 3 Distal 4 Metacarpal Triquetral Proximal 1 Distal 2 Distal 5 Middle 5 Lunate Scaphoid Trapezoid Trapezium Distal ulna
2 3 4
5 I
~
Male .. Female White DSerenc~e 1- Black _]. W h i t e _ . Difference Num- Mean Num- Mean % Di[- Z-score INum-IMean]Yum-IMeanl% Di[-] Z-score her age ber age l]ereneeldifferencel her I age ~ ber ] age IfereneeIdifference 62 1.15 56 1.28 88 1.22 202 1.26 62 1.29 94 1.37 88 1.72 94 1.53 88 1.65 88 1.65 117 1.93 159 1.69 159 1.99 153 2.03 444 2.67 673 2 . 3 3 235 2.50 257 2.46 187 2.49 352 2.90 944 3.66 754 5.48 682 5.68 942 5.83 1008 6.72
Mean per cent difference
293 293 293 565 293 475 475 475 445 445 445 565 445 445 748 1409 646 748 866 866 1379 1872 1450 1872 1630
1.33 1.42 1.51 1.55 1.57 1.67 1.73 1.82 1.85 1.88 1.96 2.08 2.11 2.12 2.56 2.70 2.74 2.97 3.01 3.01 4.01 6.07 6.16 6.22 7.21
+ 9 + 6 +13 +13 +12 +12 0 +11 + 8 + 9 + 1 +14 + 4 + 3 - 3 +11 + 7 +14 +14 + 3 + 7 + 9 + 7 + 6 + 6
+0.52 +0.35 +0.71 +0.62 +0.55 +0.53 +0.02 +0.52 +0.42 +0.46 +0.06 +0.55 +0.21 +0.15 -0.12 +0.22 +0.26 +0.59 +0.60 +0.10 +0.21 +0.42 +0.41 +0.25 +0.39
+ 7.8
Mean Z-score difference
27 27 27 27 27 27 27 49 68 68 87 68 68 68 68
262 68 87 87 87 934 913 742
742 907
0.72 91 0.75 91 0.79 91 0.72 135 0.88 91 0.86 91 0.92 91 1.05 91 0.94 234 0.95 135 0.99 234 1.05 234 0.99 234 1.14 234 1.22 392 1.36 576 1.18 316 1.34 384 1.35 384 1.22 384 2.46 994 3.92 942 4.14 911 4.16 1174 5.59 1 1 4 3
0.94 0.91 0.96 1.05 1.05 1.05 1.17 1.16 1.19 1.18
1.22 1.19 1.40 1.43 1.33 1.71 1.69 1.86 1.85 1.74 2.99 4.38 4.40 4.24 5.79
+13 +10 +10 +18 + 9 +11 +13 + 6 +13 +12 +12 + 7 +19 +13 + 5 +14 +21 +20 +19 +21 +14 + 9 + 5 + 2 + 3
+0.69 +0.49 +0.55 +1.00 +0.61 +0.68 +0.84 +0.44 +0.59 +0.61 +0.50 +0.54 +0.84 +0.58 +0.27 +0.31 +0.85 +0.83 +0.85 +0.89 +0.42 +0.4i +0.23 +0.06 +0.17
+12.0 +0.36
+0.57
Per cent differences are conception corrected, using the mean plus 0.75 years, Z-score differences are expressed in standard deviation units, e.g., absolute differences divided by the standard deviation for the center in question.
d e v e l o p m e n t approximates half a standard deviation or Z score. T h e r e is no falling-off in the Black children at 6 months, 1 year, 18 months, or even at 3 years, as earlier studies from Africa h a v e suggested. T h e d a t a are internally consistent. F o r the age range considered, roughly ! to 7 years, children of largely African ancestry in the U n i t e d States are not only a d v a n c e d skeletally, but they are also taller as measured b y standing height or stature. T h e height excess of Ne g r o infants and children averages 0.77 cm. for boys and 1.20 cm. for girls, or close to 0.25 standard deviations (Z scores). As with ossification timing, N e g r o girls are m o r e a d v a n c e d i n stature t h a n Negro boys. T h e statural a d v a n c e is present t h r o u g h the tenth year in the present subject sample.
T h e m e a n Orshansky I n d e x for the A m e r ican N e g r o families sampled is 1.06, close to the defined " p o v e r t y level" of 1.00. N e a r ly half of the Black boys and girls in the sample were below poverty. I n Contrast, the m e a n i n c o m e / n e e d s ratio for the W h i t e families was 1.70, in this comparison. Despite the u n f a v o r a b l e difference in socioeconomic Status or i n c o m e / n e e d s , the poor Black children 'are a d v a n c e d skeletally, over the notso-poor W h i t e boys and girls. I t is currently difficult to assess the past literature, some of it nearly 50 years old, with a view to c o m p a r i n g the socioeconomic status of "unselected" Black an d W h i t e ,neonates, inf~tnts, and children in varied hospital studies here and abroad. I t is difficult to c o m p a r e nutritional quality and environm e n t a l quality of Black boys and girls from
9 68
G a r n e t al.
South Africa in 1952 and Brush Foundation White children radiographed prior to 1942. For obvious reasons we have not attempted a detaiIed comparison with our previous norms for postnatal ossification, derived from Fels Institute studies of well-nourished children? 4 T h e data clearly indicate American N e g r o advancement of 25 postnatal handwrist centers, including round bones, epiphyses of the long bones, and epiphyses of the short bones in each ray or digit. W h a t we have here is compelling evidence for Negro advancement of postnatal ossification, through and beyond the fifth and sixth years, with the n u m b e r of subjects (N) approaching or exceeding 1,000 for the latest appearing centers. I n the United States, in 1968 to 1970, comparing subjects of the lower socioeconomic groupings, Negro children are skeletally advanced through the fifth and sixth years, and they do not fall behind as African reports suggest. Since ossification timing (age at appearance of postnatal ossification centers) is not necessarily correlated with later osseous events, we may not project these findings at 1 to 6 years to later ages, e.g., 6 to 13.1~ Available literature on later skeletal developm e n t in Negro boys and girls is equivocal. T h e data suggest continuing advancement in Black girls, but not necessarily in Black boys? 6 Cross-racial comparisons of growth, development, and maturation are complicated when per capita income, utilization of the food dollar and food selection, and childrearing patterns are systematically different. Reliance on packaged and snack foods m a y widen the poverty gap. I n the present study we simply report that near-poverty level Negro boys and girls are approximately 0.5 S.D. ahead of somewhat higher i n c o m e / needs level White boys and girls in age at appearance of postnatal ossification centers. If the developmental difference is purely genetic, the approximately 0.5 Negro advance in ossification timing would be raised to 0.63 by correction for the 10 to 25 per cent accretion of E u r o p e a n genes. Again, correction for the 0.6 difference in income/needs
The Journal of Pediatrics June 1972
ratio (approximately $480 per person) raises the apparent Black-White difference in ossification to 0.67 Z scores or standard scores. I n any event, the developmental advancem e n t of Black boys and girls is in the opposite direction from simple expectancy, and it has bearing on the radiographic method of development appraisal. The authors are grateful to Mr. Richard L. Miller of the computer facility of the Center for Human Growth and Development for development of the program for the computation of M and ~r, to Marcia Lux for assistance in the data compilation, and to Shirley M. Garrett for assistance in the manuscript completion. REFERENCES
1. Garn, S. M.: Physical growth and development, Am. J. Phys, Anthropol. 10: 169, 1952. 2. Tanner, J. M.: Growth at adolescence, ed. 2, Oxford, 1962, Blackwell Scientific Publications. 3. Falkner, F., Pernot-Roy, M. P., Habich, H., S6n6cal, J., and Mass6, G.: Some international comparisons of physical growth in the two first years of life, Courrier 8: 1, 1958. 4. Jones, P. R. M., and Dean, R. F. A.: The effects of Kwashiorkor on the development of the bones of the hand, J. Trop. Pediatr.
2: 51, 1956. 5. Beresowski, A., and Lnndie, J. K.: Sequence in the time of ossification of the carpal bones in 705 African children from birth to six years of age, S. Afr. J. Med. Sci. 17: 25, 1952. 6. Tobias, P. V.: Some aspects of the biology of the Bantu-speaking African, Leech 28: 3, 1958. 7. Hess, A. F., and Weinstoek, M.: A comparison of the evolution of carpal centers in White and Negro newborn infants, Am. J. Dis. Child. 29: 347, 1925. 8. Dunham, E. C., Jenss, R. M., and Christie, A. U.: A consideration of race and sex in relation to the growth and development of infants, J. P~mAWm 14: 156, 1939. 9. Kelly, I-I. J., and Reynolds, L.: Appearance and growth of ossification centers and increases in the body dimensions of White and Negro infants, Am. J. Roentgenol. Radium Ther. Nucl. Med. 57: 477, 1947. 10. Christie, A.: Prevalence and distribution of ossification centers in the newborn infant, Am. J. Dis. Child. 77: 355, 1949. 11. Reed, T. E.: Caucasian genes in American Negroes, Science 165: 762, 1969. 12. Abramowitz, M., and Stegun, I. A.: Handbook 9 of mathematical functions, Washington, 1964, U. S. Government Printing Office. 13. Orshansky, M.: Counting the poor: Another
Volume 80 Number 6
Skeletal development in low-income Negro children
look at the poverty profile, Soc. Sec. Bull. 28: 3, 1965. 14. Garn, S. M., Rohmann, C. G., and Silverman, F. N.: Radiographic standards for postnatal ossification and tooth calcification, Med. Radiogr. Photogr. 43: 45, 1967. 15. Malina, R. M.: Skeletal maturation rate in
969
North American Negro and White children, Nature 223: 1075, 1969. 16. Malina, R. M.: Skeletal maturation studied longitudinally over one year in American Whites and Negroes six through thirteen years of age, Hum. Biol. 42: 377, 1970.
965
Advanced skeletal development in low-income Negro cl 'ldren The age at radiographic appearance o[ postnatal ossification centers o] 1,942 American Negro children proved to be advanced over the age at appearance in the same hand centers in 3,046 boys and girls o[ European ancestry, by approximately 0.5 standard deviations, even though the socioeconomic status o[ the Negro children was 0.6 income/ needs units lower than that o[ the Caucasian sample.
Stanley M. Garn, Ph.D.,* Sam T. Sandusky, B.A., Jerrold M. Nagy, A.B., and
Mary B. McCann, M.D., A n n Arbor, Mich., and Atlanta, Ga.
B o , z s a N D G I R L S of African ancestry tend to be advanced in postnatal ossification? ,2 Such developmental advancement has been reported from West Africa, 3 East Africa, 4 and South Africa. 5, 6 Osseous advancement was reported as early as 1925 for American Negro children, who are largely of West African ancestry, 7-~~ but with a 20 to 25 per cent accretion of European genes? ~ However, it is not clear how long and to what extent advanced ossification continues. Some of the studies have been concerned only with the neonate and with the earliest appearing h i p and hand centers J, s, 10 Others have reported a shift from comparative skeletal advancement to relative delay by the middle or the end of the first year, s by 18 months, 3 or by three years. In most studF r o m the Center for H u m a n G r o w t h a n d D e v e l o p m e n t , T h e University of M i c h i g a n , and the Center for Disease Control.
Supported by Contract HSM 110-69-22 with the Center for Disease Control, Atlanta, Ga. "~Reprint address: Center for Human Growth and Development, The Univers:ty o] Michigan 611 Church St., Ann Arbor, Mich. 48104.
ies the number of Negro children was small at each age interval, and adequate socioeconomic data have been invariably lacking. In the present comparison, we have the advantage of a rather large sample size (N 5,000), a broad sampling base--from Massachusetts to California, and socioeconomic data for the generally low-income families. The indications are that at a mean income/needs ratio near the poverty line, children of largely African ancestry are impressively advanced in the age at appearance of 25 postnatal ossification centers of the hand and wrist.
MATERIALS AND METHODS This investigation is based upon the age at appearance of 25 postnatal ossification centers of the hand and wrist as seen in the radiographs of 4,988 participants in the Multistate Nutrition S u ~ e y of 1968 to 1970. Recording the presence or absence of each postnatal ossification center on optical scanning cards, and transferring the dichotomous (present-absent) data to magnetic tape, two Vol. 80, No. 6, pp. 965-969
966
Garnet
The Journal of Pediatrics June 1972
al.
measures were computed by the I B M 360/ 67 computer. One was M, corresponding to the arithmetic mean in a Gaussian distribution. The second measure was _~, as derived from the cumulative frequency curve, 12 and mathematically defined as: 1
K~/2II with K being the average slope of the curve. Throughout the study, age (C.A.) was calculated as the exact age (using both birth date and examination date) : Subjects lacking either were excluded from the computation. The sexes were separated, as were participants of European ancestry ("Whites") and those of largely African ancestry, i.e., American Negroes or "Blacks" as currently defined. I n all there were 3,046 Whites, largely derived from Northern European ancestors, and 1,942 Blacks, largely of West African ancestral origin. 11 The limits of individual cumulative frequency curves were the earliest age at which each center was observed and the first age at which 100 per cent of radiographs evidenced the center in question. Relative income or (income/needs) was individually expressed by the Orshansky Index, a measure that takes family size and age of family members into account. 13 The participating states were Massachusetts, New York, Michigan, Kentucky, West Virginia, South Carolina, Texas, California, and Washington; the metropolitan areas of Bos~ ton, New York, Detroit, and Los Angeles were included. In expressing the percentage difference in postnatal ossification timing between Blacks and Whites, a value of 0.75 years was added to each mean age in order to avoid implausibly large percentage differences that ensue when birth age is taken as zero time. Such "conception correction" gives a more useful measure of relative timing between races and between sexes? 4 RESULTS
As shown in Table I, ossification in children of largely African ancestry occurs at an
earlier mean age than in boys and girls of European ancestral origin. Excluding the capitate, hamate, and distal epiphysis of the radius, for which comparative data were too meager, this generalization holds for both sexes, and with but one exception out of 50 race-sex comparisons. For Black boys, the conception-corrected advance in ossification timing averages 7.8 per cent; the largest relative differences are exhibited by the epiphysis of the fifth metacarpal and by the epiphyses of the distal segments of the second and fifth fingers. For Black girls, the comparable advancement in postnatal ossification timing was 18 per cent or more for six ossification centers, and averaged 12.0 per cent for all 25 centers. More usefully expressed in Z scores (i.e., standard deviation units), nine centers were advanced 0.5 S.D. or more in Black boys, and 16 postnatal ossification centers were comparably advanced in Black girls. Overall, the developmental skeletal advancement averaged half a standard deviation, i.e., +0.36 S.D. in Black boys and +0.57 S.D. in Black girls. The advancement in postnatal ossification timing in Black boys and girls was highly significant by any reasonable test, the sign test alone being 49:1 as compared with the chance or 25:25 distribution. It was, moreover, usefully large from a clinical point of view, since the difference is half a standard deviation. If there is a drop-off in relative skeletal advancement of Black boys and girls as often suggested, it is long after the third year. Within the limits of the study, i.e., the appearance of the distal epiphysis of the ulna at 5.6 to 7.2 years, Black boys and girls were still ahead of their White counterparts (Table I ) . DISCUSSION
The radiographic findings in this multistate nutritional survey, involving nearly 5,000 boys and girls, are both simple and definitive. The average age at appearance o f 25 postnatal hand-wrist centers is nearly 10 per cent ahead in children of largely African ancestry. The advancement in skeletal
Volume 80 Number 6
Skeletal d e v e l o p m e n t in low-income Negro children
96 7
T a b l e I. B l a c k - W h i t e differences in ossification t i m i n g
Black
Ossification center Proximal 3 Proximal 2 Proximal 4 Distal 1 Metacarpal Metacarpal Proximal 5 Metacarpal Middle 3 Middle 4 Middle 2 Metacarpal Distal 3 Distal 4 Metacarpal Triquetral Proximal 1 Distal 2 Distal 5 Middle 5 Lunate Scaphoid Trapezoid Trapezium Distal ulna
2 3 4
5 I
~
Male .. Female White DSerenc~e 1- Black _]. W h i t e _ . Difference Num- Mean Num- Mean % Di[- Z-score INum-IMean]Yum-IMeanl% Di[-] Z-score her age ber age l]ereneeldifferencel her I age ~ ber ] age IfereneeIdifference 62 1.15 56 1.28 88 1.22 202 1.26 62 1.29 94 1.37 88 1.72 94 1.53 88 1.65 88 1.65 117 1.93 159 1.69 159 1.99 153 2.03 444 2.67 673 2 . 3 3 235 2.50 257 2.46 187 2.49 352 2.90 944 3.66 754 5.48 682 5.68 942 5.83 1008 6.72
Mean per cent difference
293 293 293 565 293 475 475 475 445 445 445 565 445 445 748 1409 646 748 866 866 1379 1872 1450 1872 1630
1.33 1.42 1.51 1.55 1.57 1.67 1.73 1.82 1.85 1.88 1.96 2.08 2.11 2.12 2.56 2.70 2.74 2.97 3.01 3.01 4.01 6.07 6.16 6.22 7.21
+ 9 + 6 +13 +13 +12 +12 0 +11 + 8 + 9 + 1 +14 + 4 + 3 - 3 +11 + 7 +14 +14 + 3 + 7 + 9 + 7 + 6 + 6
+0.52 +0.35 +0.71 +0.62 +0.55 +0.53 +0.02 +0.52 +0.42 +0.46 +0.06 +0.55 +0.21 +0.15 -0.12 +0.22 +0.26 +0.59 +0.60 +0.10 +0.21 +0.42 +0.41 +0.25 +0.39
+ 7.8
Mean Z-score difference
27 27 27 27 27 27 27 49 68 68 87 68 68 68 68
262 68 87 87 87 934 913 742
742 907
0.72 91 0.75 91 0.79 91 0.72 135 0.88 91 0.86 91 0.92 91 1.05 91 0.94 234 0.95 135 0.99 234 1.05 234 0.99 234 1.14 234 1.22 392 1.36 576 1.18 316 1.34 384 1.35 384 1.22 384 2.46 994 3.92 942 4.14 911 4.16 1174 5.59 1 1 4 3
0.94 0.91 0.96 1.05 1.05 1.05 1.17 1.16 1.19 1.18
1.22 1.19 1.40 1.43 1.33 1.71 1.69 1.86 1.85 1.74 2.99 4.38 4.40 4.24 5.79
+13 +10 +10 +18 + 9 +11 +13 + 6 +13 +12 +12 + 7 +19 +13 + 5 +14 +21 +20 +19 +21 +14 + 9 + 5 + 2 + 3
+0.69 +0.49 +0.55 +1.00 +0.61 +0.68 +0.84 +0.44 +0.59 +0.61 +0.50 +0.54 +0.84 +0.58 +0.27 +0.31 +0.85 +0.83 +0.85 +0.89 +0.42 +0.4i +0.23 +0.06 +0.17
+12.0 +0.36
+0.57
Per cent differences are conception corrected, using the mean plus 0.75 years, Z-score differences are expressed in standard deviation units, e.g., absolute differences divided by the standard deviation for the center in question.
d e v e l o p m e n t approximates half a standard deviation or Z score. T h e r e is no falling-off in the Black children at 6 months, 1 year, 18 months, or even at 3 years, as earlier studies from Africa h a v e suggested. T h e d a t a are internally consistent. F o r the age range considered, roughly ! to 7 years, children of largely African ancestry in the U n i t e d States are not only a d v a n c e d skeletally, but they are also taller as measured b y standing height or stature. T h e height excess of Ne g r o infants and children averages 0.77 cm. for boys and 1.20 cm. for girls, or close to 0.25 standard deviations (Z scores). As with ossification timing, N e g r o girls are m o r e a d v a n c e d i n stature t h a n Negro boys. T h e statural a d v a n c e is present t h r o u g h the tenth year in the present subject sample.
T h e m e a n Orshansky I n d e x for the A m e r ican N e g r o families sampled is 1.06, close to the defined " p o v e r t y level" of 1.00. N e a r ly half of the Black boys and girls in the sample were below poverty. I n Contrast, the m e a n i n c o m e / n e e d s ratio for the W h i t e families was 1.70, in this comparison. Despite the u n f a v o r a b l e difference in socioeconomic Status or i n c o m e / n e e d s , the poor Black children 'are a d v a n c e d skeletally, over the notso-poor W h i t e boys and girls. I t is currently difficult to assess the past literature, some of it nearly 50 years old, with a view to c o m p a r i n g the socioeconomic status of "unselected" Black an d W h i t e ,neonates, inf~tnts, and children in varied hospital studies here and abroad. I t is difficult to c o m p a r e nutritional quality and environm e n t a l quality of Black boys and girls from
9 68
G a r n e t al.
South Africa in 1952 and Brush Foundation White children radiographed prior to 1942. For obvious reasons we have not attempted a detaiIed comparison with our previous norms for postnatal ossification, derived from Fels Institute studies of well-nourished children? 4 T h e data clearly indicate American N e g r o advancement of 25 postnatal handwrist centers, including round bones, epiphyses of the long bones, and epiphyses of the short bones in each ray or digit. W h a t we have here is compelling evidence for Negro advancement of postnatal ossification, through and beyond the fifth and sixth years, with the n u m b e r of subjects (N) approaching or exceeding 1,000 for the latest appearing centers. I n the United States, in 1968 to 1970, comparing subjects of the lower socioeconomic groupings, Negro children are skeletally advanced through the fifth and sixth years, and they do not fall behind as African reports suggest. Since ossification timing (age at appearance of postnatal ossification centers) is not necessarily correlated with later osseous events, we may not project these findings at 1 to 6 years to later ages, e.g., 6 to 13.1~ Available literature on later skeletal developm e n t in Negro boys and girls is equivocal. T h e data suggest continuing advancement in Black girls, but not necessarily in Black boys? 6 Cross-racial comparisons of growth, development, and maturation are complicated when per capita income, utilization of the food dollar and food selection, and childrearing patterns are systematically different. Reliance on packaged and snack foods m a y widen the poverty gap. I n the present study we simply report that near-poverty level Negro boys and girls are approximately 0.5 S.D. ahead of somewhat higher i n c o m e / needs level White boys and girls in age at appearance of postnatal ossification centers. If the developmental difference is purely genetic, the approximately 0.5 Negro advance in ossification timing would be raised to 0.63 by correction for the 10 to 25 per cent accretion of E u r o p e a n genes. Again, correction for the 0.6 difference in income/needs
The Journal of Pediatrics June 1972
ratio (approximately $480 per person) raises the apparent Black-White difference in ossification to 0.67 Z scores or standard scores. I n any event, the developmental advancem e n t of Black boys and girls is in the opposite direction from simple expectancy, and it has bearing on the radiographic method of development appraisal. The authors are grateful to Mr. Richard L. Miller of the computer facility of the Center for Human Growth and Development for development of the program for the computation of M and ~r, to Marcia Lux for assistance in the data compilation, and to Shirley M. Garrett for assistance in the manuscript completion. REFERENCES
1. Garn, S. M.: Physical growth and development, Am. J. Phys, Anthropol. 10: 169, 1952. 2. Tanner, J. M.: Growth at adolescence, ed. 2, Oxford, 1962, Blackwell Scientific Publications. 3. Falkner, F., Pernot-Roy, M. P., Habich, H., S6n6cal, J., and Mass6, G.: Some international comparisons of physical growth in the two first years of life, Courrier 8: 1, 1958. 4. Jones, P. R. M., and Dean, R. F. A.: The effects of Kwashiorkor on the development of the bones of the hand, J. Trop. Pediatr.
2: 51, 1956. 5. Beresowski, A., and Lnndie, J. K.: Sequence in the time of ossification of the carpal bones in 705 African children from birth to six years of age, S. Afr. J. Med. Sci. 17: 25, 1952. 6. Tobias, P. V.: Some aspects of the biology of the Bantu-speaking African, Leech 28: 3, 1958. 7. Hess, A. F., and Weinstoek, M.: A comparison of the evolution of carpal centers in White and Negro newborn infants, Am. J. Dis. Child. 29: 347, 1925. 8. Dunham, E. C., Jenss, R. M., and Christie, A. U.: A consideration of race and sex in relation to the growth and development of infants, J. P~mAWm 14: 156, 1939. 9. Kelly, I-I. J., and Reynolds, L.: Appearance and growth of ossification centers and increases in the body dimensions of White and Negro infants, Am. J. Roentgenol. Radium Ther. Nucl. Med. 57: 477, 1947. 10. Christie, A.: Prevalence and distribution of ossification centers in the newborn infant, Am. J. Dis. Child. 77: 355, 1949. 11. Reed, T. E.: Caucasian genes in American Negroes, Science 165: 762, 1969. 12. Abramowitz, M., and Stegun, I. A.: Handbook 9 of mathematical functions, Washington, 1964, U. S. Government Printing Office. 13. Orshansky, M.: Counting the poor: Another
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Skeletal development in low-income Negro children
look at the poverty profile, Soc. Sec. Bull. 28: 3, 1965. 14. Garn, S. M., Rohmann, C. G., and Silverman, F. N.: Radiographic standards for postnatal ossification and tooth calcification, Med. Radiogr. Photogr. 43: 45, 1967. 15. Malina, R. M.: Skeletal maturation rate in
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North American Negro and White children, Nature 223: 1075, 1969. 16. Malina, R. M.: Skeletal maturation studied longitudinally over one year in American Whites and Negroes six through thirteen years of age, Hum. Biol. 42: 377, 1970.