Cortical bone loss and measurements of the second metacarpal bone. I. Comparisons between adult Guamanian Chamorros and American caucasiansкод для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 59:461-466(1982) Cortical Bone Loss and Measurements of the Second Metacarpal Bone. 1. Comparisons Between Adult Guamanian Chamorros and American Caucasians C. C . PLATO, R. M. GARRUTO, R. T. YANAGIHARA, K.-M. CHEN, J. L. WOOD, D. C. GAJDUSEK, AND A. H. NORRIS Gerontology Research Center, Natimal Institute on Aging, National Institutes of Health, Baltimore, Maryland (C.C.P., J.L. W., A.H. N.), and Laboratory of Central Nervous System Studies, National Institute of Neurolouical and Communicative Disorders and Stroke. National Institutes of Heal&, Bethesda, Maryland, and the NINCDS Research Center, Tamuning, Cuam (R.M.G., R.T.Y., K-M.C., D.C.G.) KEY WORDS Bone loss, Osteoporosis, Bone measurements, Guamanians, Caucasians ABSTRACT The amount of radiographically detectable cortical bone, as determined by measurements of the second metacarpal, was evaluated in 42 male and 45 female Guamanian Chamorros and compared with the degree of bony demineralization in U.S. Caucasians participating in the Baltimore Longitudinal Study on Aging of the Gerontology Research Center. All Chamorros were individually matched to the Caucasian participants for age, sex, and menopause status. Chamorros of both sexes showed bilateral asymmetry in bone measurements and in the amount of cortical bone. Both Chamorro and Caucasian males had longer second metacarpals and more cortical bone than females. Caucasian males, however, had longer and larger second metacarpals than Chamorro males. Despite differences in the length and total width, Chamorro and Caucasian participants generally showed no significant differences in the amount of cortical bone or percent cortical area in the second metacarpal, suggesting that larger bones may not always indicate greater cortical mass. Although cross-sectional data suggested apparent age differences in the onset and rate of bone loss between Chamorros and Caucasians, the numbers of participants were too small to allow meaningful age-by-age statistical comparisons. The causes of and pathogenetic relationship between amyotrophic lateral sclerosis and parkinsonism-dementia - two relentlessly progressive, invariably fatal neurological diseases occurring in high incidence among the Chamorro people of Guam - remain obscure. Because of the unusually low levels of alkaline earth metals, particularly calcium and magnesium, in samples of soil and drinking water from southern Guam and two other geographical isolates of motor neuron disease and parkinsonian syndromes (Gajdusek and Salazar, 1982; Iwata et al., 1978; Shiraki and Yase, 1975), recent studies have focused on the evaluation of mineral metabolism in patients with these disorders (Yanagihara et al., 1981). As part of these studies, bilateral hand x-rays have been obtained from Chamorro patients and nonaffected controls for comparative 0002-948318215904-0461$02.00 0 1982 ALAN R. LISS, INC. measurements of bone and for determination of cortical bone mass. These data are currently being analyzed and will be reported separately. The purpose of the present report is to describe measurements of the second metacarpal bone in neurologically normal Guamanian Chamorros and to compare them with those obtained from an age-, sex-, and menopause status-matched group of Caucasians participating in the Baltimore Longitudinal Study on Aging of the Gerontology Research Center (GRC). MATERIALS AND METHODS Bilateral hand radiographs were obtained from 42 adult male and 45 adult female GuaReceived March 1, 1982; accepted August 2, 1982 462 C.C. PLAT0 ET AL. manian Chamorros ranging in age from 21 to 70 years. All participants were neurologically normal, and were either hospital employees or individuals who had accompanied their relatives or friends to the Guam Memorial Hospital. Informed consent was obtained from all participants. The x-rays from each participant were individually matched with the x-rays obtained from GRC Caucasians of the same sex and similar age. In certain cases, especially at younger ages, it was not possible to pair Guamanians with Caucasians of exactly the same age, but in no instance was the intrapair age difference greater than 5 years. Female Chamorros and Caucasians were also matched for menopausal status. Since all but one of the Chamorro women experienced natural menopause, Caucasian women with hysterectomies or other forms of induced menopause were excluded from the study. Although women were matched for menopausal status at the time of x-ray, it was not possible to match them for age at onset of menopause. The average age at onset of menopause was 46.6 years in Chamorros, and 51.6 years in Caucasians. The GRC participants were of good general health and of above-average education and socioeconomic status. Detailed descriptions of this group have been previously reported (Stone and Norris, 1966; Rowe et al., 1976). Hand radiographs were taken posteroanteriorly on Kodak RP/S X-Omat film at an average exposure of 1.0 second at 100 mA and 60 kVp without intensifying screens and were developed at the Baltimore City Hospitals. Measurements of total width (TW), medullary width (MW), and length (LEN) at the midshaft of the second metacarpal bone were performed “blindly” by the same individual (Plato et al., 1980). Combined cortical thickness (CCT) was derived by subtracting MW from TW (i.e., CCT = TW-MW). Percent cortical area (PCA), the ratio of cortical area to total area, was calculated using the formula, PCA = (TW12 - (MW12/(TW12.To a great extent PCA is independent of body size. Further descriptions of these measurements and methods for determining the bone’s midshaft are given elsewhere (Garn et al., 1964; Garn, 1970; Plato and Norris, 1980). Because of the small sample size, and since Guam and GRC participants were individually matched for age, sex, and menopause status, the data were not separated into age groups. Bilateral differences among Guamanians, as well a s differences between Guam and GRC samples, were compared using the Student’s t-test. Regression lines were derived using a second-degree polynomial model, Y = bo + blX + bzX2 (Ostle, 1954). RESULTS AND DISCUSSION Guam-GRC comparisons Table 1 compares measurements of the second metacarpal bone in the left and right hands, respectively, of Guamanian and Caucasian males. Caucasian males had significantly wider and longer second metacarpal bones than their Chamorro counterparts. Differences in MW, CCT, and PCA were not significant. Caucasian females also had longer and wider bones than Chamorro females (Table 2). Although Caucasian women had greater values for all one-parameter variables (TW, MW, CCT, and LEN) than Guamanian women, they had smaller (although nonsignificant) values for PCA, which depends on two parameters (cortical area and total area). In general, Guamanian women had smaller and more compact bone than Caucasian women. Paired bilateral comparisons Paired bilateral differences 0or mean differences between measurements of the right and left hands of the same individual are shown in Table 3. A positive d indicates a higher mean value in the right hand. Among Guamanians, significant bilateral differences were found for TW in both sexes, MW in males, and CCT in females. Bilateral differences in LEN and PCA were not significant in either sex. In the GRC group (not shown in the tables), most d values were also positive. However, significant bilateral differences were seen only for TW in males (P< 0.01) and LEN in females (P < 0.05). Regression analysis Postulating a second-order binomial function, we fitted a regression curve of each variable on age. Each distribution was then tested for best fit by both linear and curvilinear (quadratic) regression. Predicted values for MW, CCT, and PCA of both Caucasian and Guamanian males and females best fit the models of curvilinear regression on age. Predicted values for CCT are shown in Figure 1. Only curves for the left hands are presented, but curves for the right hands were similar. The regression slopes of the respective variables for Guamanian and GRC males and females showed no significant differences, mainly because of the wide intragroup variability and the small numbers. Despite the lack of statistical differences between the regres- 463 BONE LOSS IN GUAMANIANS AND CAUCASIANS TABLE 1. Comparisons between second metacarpal bone measurements of42 age-matched Guam and GRC male Dairs Second metacarpal bone measurements Left hands Total width (mm) Medullary width (mm) Combined cortical thickness (mm) Length (mm) Percent cortical area (%) Right hands Total width (mm) Medullary width (mm) Combined cortical thickness (mm) Length (mm) Percent cortical area (%) t 0.01. 't Values for Paired Comparisons Guam-GRC differences Group comparisons Guam GRC t S.E. Mean S.E. Mgan (d) S.E. Mean (S4 values' 8.80 3.29 5.51 0.10 0.17 0.14 9.39 3.70 5.69 0.11 0.15 0.12 -0.59 -0.42 -0.17 0.16 0.23 0.18 -3.37** - 1.84 -0.95 65.83 85.00 0.60 1.31 70.93 83.88 0.63 1.03 -4.97 1.09 0.81 1.65 -6.12** 0.66 9.11 3.54 5.57 0.10 0.16 0.14 9.71 4.02 5.69 0.12 0.16 0.14 -0.60 -0.48 -0.12 0.14 0.24 0.20 - 1.99 66.03 84.02 0.45 1.25 71.31 82.12 0.62 1.45 -5.28 - 1.90 0.74 2.06 -7.13** -0.92 -4.40** -0.58 a and s;l were calculated before rounding off. TABLE 2. Comparisons between second metacarpal bone measurements of 45 age- and menopausal status-matched Guam and GRC female pairs Paired comparisons Guam-GRC differences Group comparisons Second metacarpal bone measurements Left hands Total width (mm) Medullary width (mm) Combined cortical thickness (mm) Length (mm) Percent cortical area (%) Right hands Total width (mm) Medullary width (mm) Combined cortical thickness (mm) Length (mm) Percent cortical area (%) Guam Mean GRC S.E. t values' Mean S.E. Mean S.E. (d) 7.80 2.96 4.84 0.07 0.14 0.10 8.02 2.90 5.12 0.08 0.14 0.11 -0.22 0.06 -0.28 0.10 0.16 0.13 -2.24* 0.39 -2.22* 61.39 84.76 0.44 1.18 65.01 86.11 0.54 1.12 - 1.35 -3.61 0.79 1.32 -4.58** - 1.02 8.08 3.04 5.04 0.09 0.15 0.12 8.17 2.98 5.20 0.07 0.15 0.12 -0.09 -0.07 -0.15 0.11 0.19 0.16 -0.79 -0.35 -0.97 61.56 84.88 0.41 1.29 65.21 85.75 0.57 1.26 -3.65 -0.87 0.78 1.54 -4.66** -0.56 (%I) *P < 0.05. **P < 0.01. 't Values for and sa were calculated before rounding off. a sion slopes of Guamanians and Caucasians, certain trends are worthy of comment. 1.) After attainment of maturity, neither TW nor LEN changed Significantly, regardless of hand, sex or population group. At all ages, TW and LEN were greater in Caucasians than Guamanians and greater in the right than the left hands. 2.) Males and females of both population groups, over the age of 40 years showed increasing MW with age. Males younger than 40 years had significantly larger MW than females, but this difference gradually dimin- ished with advancing age owing to accelerated bone resorption from the endosteal surface in postmenopausal women. Guamanian males and females under the age of 35 years had larger MW than their respective Caucasian counterparts. This relationship reversed after the age of 50 to 60 years. 3.) The distribution of predicted values for CCT (Fig. 1) gives the degree of bone loss with age, which reflects changes in MW since TW does not change with age. With the exception of the Guamanian males younger than 40 years, males of both ethnic groups had more 464 C . C . PLAT0 ET AL. TABLE 3. Paired bilateral dqferences in measurements ofthe second metacarpal bone in Guamanian Chamorros Second metacarpal bone measurements Male (N = 42) Total width (mm) Medullary width (mm) Combined cortical thickness (mm) Length (mm) Percent cortical area (%) Female (N = 45) Total width (mm) Medullary width (mm) Combined cortical thickness (mm’, Length (mm) Percent cortical area (%) Paired bilateral comparisons (right-left differences) Mgan S.E. t (d) (sx) values’ 4.45** 0.06** 0.84 0.31 0.25 0.06 0.07 0.08 0.07 0.20 -0.95 0.34 0.56 0.29 0.08 0.21 0.05 0.09 0.09 5.51** 0.88 2.26* 0.17 0.12 0.17 0.80 0.98 0.15 0.58 - 1.69 > P 2 0.01. **P < 0.01. ‘t Values ford and s;, were calculated before rounding off. *0.05 -E -E 7.0 ‘z 6.0 E 8 5.0 bone and lost less bane with age than did females. The reason for the smaller amount of cortical bone in younger Guamanian males is not clear from the present data. I t may reflect secular changes in the Guamanian society or enviranment. The possibility of secular effects needa to be given further consideration since Gumanian males in the age groups having low values for CCT were born after the end of World War 11, which marked the beginning of rofound sociocultural changes on Guam. early every aspect of daily life of both sexes, including nutritional, occupational, residential, and recreational preferences or habits, was affected by these changes, but the major impact was upon men. At younger ages, Caucasian females had greater predicted CCT than Chamorro females, but after age 60 the situation was reversed and Caucasian women had less cortical bone than their Guamanian counterparts. Both female groups began to lose cortical bone after the age of 40, but with increasing age Cauca- R v) 3 ....J ..-. 3 -1 -0.-C. -0 e s m 8 e L e 4.0 3.0 , I 20 30 50 40 60 70 AGE (years) Fig. 1. Predicted combined cortical thickness of the left second metacarpal bone of male and female Chamorros (Guam) and Caucasians (GRC). The curvilinear regression equations are Guam males: Y = 2.393 + 0.148X - 0.0016X2,r2 = 0.18, P < 0.02; Guam females: Y = 5.443 + 0.0032X - 0.0003X2, r2 = 0.33, P < 0.001. GRC males: Y = 7.463 - 0.0527X + 0.0003X2, r2 = 0.17, P < 0.03; GRC females: Y = 3.884 + 0.0954X 0.0014X2, r2 = 0.44, P < 0.001. BONE LOSS IN GUAMABiIANS AND CAUCASIANS sian females lost bone more rapidly than Chamorro females. It is unclear from the present data whether this differential loss of cortical bone between Chamorro and Caucasian women is due primarily to genetic or cultural factors, or to a combination of both. The regression lines for predicted PCA (which is relatively independent of bone size) followed very closely those for CCT. That is, Caucasians of both sexes had greater PCA than Chamorros during youth, but the situation was reversed after age 60. In earlier studies on measurements of the second metacarpal bone of Caucasian males and females, we demonstrated that progressive bone loss occurred with increasing age, that the TW and LEN of the second metacarpal did not change sigmfkantly after adulthood, that the second metacarpal of the right hand was larger (with greater cortical mass) than the left regardless of hand dominance, that males had longer and wider second metacarpal bones than females, and that postmenopausal women lost more bone than men of the same age (Plato et al., 1980; Plato and Nonis, 1980; Plato and Purifoy, 1982). This study c onf i i e d our earlier observations and also revealed discrete differences between bone measurements in Chamorros and Caucasians. We cannot ascertain from our sample whether these differences are due to biological variation, to sampling error, to nutritional habits, or to socioeconomic conditions. Further studies are currently under way in both populations to clarify the biological significance of these differences. ACKNOWLEDGMENTS The field assistance of Mr. Manuel T. Cruz, Mr. Francisco C. Leon Guerrero, Mr. Luis T. Munoz, Mr. Jose M. Torres, Mrs. Mary E. Hernandez, and Dr. Olivia T. Cruz of the NINCDS Research Center of Guam is gratefully acknowledged. We also thank Mr. James Pauley and the x-ray technicians of the Guam Memorial Hospital for their cooperation, Mrs. 465 Janice DiGracia and Mrs. Kathleen Fox of the Gerontology Research Center for their invaluable assistance throughout the course of this project, Dr. Larry Brant for his statistical consultation, and Miss Catherine Daum for her patient help in the preparation of the manuscript. LITERATURE CITED Gajdusek, DC, and Salazar, AM (1982) Amyotrophic lateral sclerosis and parkinsonism-dementia in high incidence among the Auyu and Jakai people of West New Guinea. Neurology 32:107-126. 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