American Journal of Epidemiology Copyright ® 1992 by The Johns Hopkins University School of Hygiene and Public Health All rights reserved
Vol. 136, No. 11 Printed in U.S.A.
Black-White Differences in Fracture Rates
Marie R. Griffin,1 Wayne A. Ray,1 Randy L. Fought,1 and L. Joseph Melton III2
To compare the incidence of all nonvertebral fractures between elderly blacks and whites, the authors conducted a retrospective cohort study among Tennessee Medicaid enrollees aged 65 years or more from 1987 through 1989. A previously validated computer algorithm identified 6,802 persons of black or white race with 7,645 new nonvertebral fractures. The incidence of all nonvertebral fractures in blacks was only half of that in whites. This finding persisted after the authors controlled for sex, age, and nursing home residence (relative risk = 0.4, 95% confidence interval 0.4-0.5). Rates were consistently lower among blacks within subgroups defined by these factors and for each of the 13 different fracture sites examined. The magnitude of the difference between blacks and whites in rates of all fractures combined and most site-specific fractures is similar to that previously reported for hip fractures. These consistent racial differences suggest a common underlying factor(s). Am J Epidemiol 1992;136: 1378-85. aged; blacks; fractures; incidence; racial stocks; retrospective studies; whites
The incidence of hip fracture is higher in whites than in blacks (1). Most studies have found rates in white women to be 2-3 times those in black women, while rates in white men are 1-2 times those in black men (26). These data are available because hip fractures are relatively common in the elderly, are easily diagnosed, and nearly always result in hospitalization, thus permitting their study with computerized hospital discharge Received for publication February 10,1992, and in final form May 19, 1992. 1 Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN. 2 Section of Clinical Epidemiology, Mayo Clinic and Mayo Foundation, Rochester, MN. Reprint requests to Dr. Marie R. Griffin, Department of Preventive Medicine, Vanderbilt University School of Medicine, A-1124 MCN, 1161 21st Avenue, Nashville, TN 37232-2637. This research was supported by grants from the Centers for Disease Control (R49/CCR403562-02-1) and the Food and Drug Administration (FD-U-000073) Dr. Marie Griffin is a Burroughs Wellcome Scholar in pharmacoepidemiology. The authors gratefully acknowledge the assistance of Susan Patterson, Janet Higdon, and De'Siree' MorganLyons with manuscript preparation
data. However, such data are inadequate for identifying fractures at other skeletal sites, which often do not result in hospital admission (7). As a consequence, these other fractures have been much less studied, even though they are associated with substantial disability and cost and together outnumber hip fractures (8). Little is known about racial differences in rates of these other fractures. To overcome this problem, we developed and validated a method of fracture identification using computerized inpatient and outpatient Medicaid and Medicare claim files which has a positive predictive value of 94 percent and an estimated sensitivity of 91 percent for all treated fractures combined (9). We thus were able to study the epidemiology of all nonvertebral fractures in the elderly Tennessee Medicaid population from 1987 through 1989. MATERIALS AND METHODS Sources of data
The study population was identified using the Tennessee Medicaid enrollment file,
1378
Black-White Differences in Fracture Rates
which includes personal identifiers and information on demographic characteristics, periods of enrollment, and (through linkage with death certificates) dates of death and coded underlying causes of death (10). Fractures were identified using Medicare (for those Medicaid recipients also enrolled in Medicare) and Medicaid claim files indicating a diagnosis of fracture coded using the International Classification of Diseases, Ninth Revision, Clinical Modification (II) or treatment for fracture coded using the Physicians' Current Procedural Terminology, Fourth Edition (12) (9, 10). Cohort definition
We studied the incidence of new fractures in the population of Tennessee Medicaid enrollees aged 65 years or more from 1987 through 1989. For each individual, persontime began during the study years when all of the following three criteria were met: attainment of age 65 years, enrollment in Medicaid for at least 365 days (to exclude persons enrolled in Medicaid because of expenses associated with a fracture), and absence of a billing code indicating a fracture in the preceding 31 days (to exclude encounters associated with fracture follow-up care). Person-time at risk for each type of fracture ended on the first of the following dates: first fracture of that type, loss of Medicaid enrollment, death, or the end of the study period (December 31, 1989). Fracture ascertainment
We used a previously developed computer algorithm to identify new fractures (9). To develop the algorithm, we identified 3,086 possible nonvertebral fractures during 1987 among persons aged 65 years or more based upon the computerized diagnostic and procedure codes. Vertebral fractures were excluded because they are often asymptomatic and frequently do not result in a medical encounter. Review of medical records for a sample of 1,440 of^the 3,086 possible fractures allowed us to develop a computer algorithm that identified new fractures with an estimated positive predictive value of 94
1379
percent and sensitivity of 91 percent. The estimated positive predictive value and sensitivity of the computer algorithm for identifying fractures at 13 specific sites (in order of their frequency) are as follows: for the hip, the positive predictive value was 98 percent and sensitivity was 97 percent; for the radius/ulna, 96 percent and 93 percent; for the humerus, 95 percent and 90 percent; ribs/sternum, 84 percent and 82 percent; pelvis, 93 percent and 89 percent; ankle, 96 percent and 78 percent; femoral shaft, 87 percent and 75 percent; hand, 86 percent and 87 percent; tibia/fibula, 79 percent and 87 percent; skull/face, 89 percent and 97 percent; foot, 95 percent and 90 percent; clavicle/scapula, 86 percent and 91 percent; and patella, 82 percent and 100 percent. For the present study, we identified the first fracture at each site for all cohort members during the study period, exclusive of vertebral fractures. Analysis
Unadjusted rates for site-specific fractures and all nonvertebral fractures were calculated by dividing the number of fractures by person-time with stratification by age, sex, and race. Summary age- and sex-adjusted rates for blacks and whites were calculated using the population structure of US whites in 1988 (13). The effects of age, sex, race, nursing home status, month (to evaluate seasonal variation), calendar year (to evaluate temporal trends), and residence (urban, suburban, or rural) on site-specific fracture rates were estimated from Poisson regression models (14) using the GLIM program (15). Month, calendar year, and residence did not influence fracture rates; the simpler model which excluded those terms gave similar results, and those results are presented here. To examine the distribution of circumstances of fracture, we used data from the 1,207 patients with confirmed fractures for whom medical records were reviewed for the validation study (9). Patients were classified by site of fracture if there was a single fracture; otherwise, they were classified as having multiple fractures.
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Griffin et al.
RESULTS
During the three study years 1987-1989, 7,424 Tennessee Medicaid enrollees aged 65 years or more had one or more nonvertebral fractures identified by the computer algorithm. This study was confined to the 6,802 persons (92 percent) of white or black race, with a total of 7,645 fractures. The incidence of new nonvertebral fractures was lower for blacks than for whites within each age and sex group (table 1), with ratios ranging from 0.6:1 to 0.4:1. The overall ratio of age- and sex-adjusted rates was 0.5:1. Within each racial group, incidence of fracture increased with age such that, among those aged 85 years or more, 4.6 percent of white males, 2.1 percent of black males, 7.0 percent of white females, and 2.8 percent of black females in this population sustained at least one nonvertebral fracture annually. The most common fractures were those of the hip, which made up 36 percent of all fractures in this age group, the radius/ulna (13 percent), the rib/sternum (11 percent), the humerus (9 percent), and the pelvis (6 percent). The other sites each accounted for less than 5 percent of all fractures (table 2). Rates of fracture occurrence varied markedly by fracture site, age, and sex (figure 1). However, for each fracture site, age- and sexspecific rates were lower in blacks than in whites. In an analysis which controlled for sex,
age, and nursing home residence, overall fracture rates in blacks were 40 percent of those of whites (relative risk = 0.4, 95 percent confidence interval 0.4-0.5) (table 2). In addition, fracture rates were lower in blacks than in whites for each fracture site, and in most instances, the differences in rates were statistically significant (table 2). After we controlled for race, age, and nursing home residence, fracture rates were significantly greater at most skeletal sites in women than in men (table 2). Men had greater rates for fractures of the skull and face, chest (rib/sternum or clavicle/scapula), and hand, although the latter difference was not statistically significant. After we controlled for race and sex, fracture rates increased with age at most sites (table 2). Only ankle fractures were significantly more common among younger individuals. The overall incidence of fractures was higher among nursing home residents, primarily because of significantly higher rates of hip, hand, femoral shaft, tibia/fibula, and skull/face fractures. However, fractures of the radius/ ulna, rib/sternum, and foot were significantly lower among nursing home residents. Of the sample of 1,207 persons with fractures for whom the medical record was reviewed, 1,048 (87 percent) were of white or black race and had the circumstances of the fracture recorded in the medical record. Eighty-seven percent of all fractures were due to falls associated with trauma conven-
TABLE 1. Age-, race-, and sex-specific and age- and sex-adjusted annual incidence rates (per 10,000 person-years) of first nonvertebral fracture among Tennessee Medicaid enrollees aged 65 years or more, 1987-1989 Whites (years)
Person-years
No of fractures
Blacks Rate
Person-years
No. of fractures
Rate
Male 65-74 75-84 >85
14,021 13,756 5,064
348 472 231
248 343 456
5,436 5,322 2,178
78 79 46
143 148 211
Female 65-74 75-84 >85
40,581 41,882 22,304
1,238 2,029 1,554
305 484 697
17,052 15,630 7,447
255 264 208
150 169 279
137,608
5,872
362
53,065
930
163
Adjusted total
Black-White Differences in Fracture Rates
1381
TABLE 2. Adjusted relative riskt of fractures at various sites, by race, sex, age, and nursing home residence, among Tennessee Medicaid enrollees aged 65 years or more, 1987-1989 Black race
Female sex
Age 75-84 years
Age >85 years
Site
RRt
95% C\%
RR
Nursing home resident
95% Cl
RR
95% Cl
RR
95% Cl
RR
95% Cl
1.3-1.5
1.9*
1.8-2.0
1.3*
1.2-1.4
Any (n = 6,802)
0.4*
0.4-0.5
1.3*
1.3-1.4
1.4*
Hip (n = 2,750) Radius/ulna (n = 1,004) Rib/sternum (n = 858) Humerus (n = 659) Pelvis (n = 443) Ankle (n = 368) Hand (n = 314) Femoral shaft (n = 275) Tibia/fibula (n = 274) Foot(n = 241) Skull/face (n = 222) Clavicle/scapula
0.4*
0.4-0.5
1.2*
1.1-1.3
2.2*
2.0-2.5
3.2*
2.8-3.5
1.8*
1.6-1.9
0.3*
0.3-0.4
2.5*
2.1-3.1
1.2*
1.0-1.3
1.2
1.0-1.4
0.8*
0.7-0.9
0.4*
0.3-0.4
0.8*
0.7-0.9
1.4*
1.2-1.6
1.9*
1.6-2.3
0.7*
0.6-0.9
0.3* 0.3* 0.7* 0.6*
0.2-0.4 0.2-0.4 0.5-0.9 0.4-0.8
1.7* 2.6* 2.4* 0.9
1.4-2.1 1.9-3.5 1.8-3.3 0.7-1.1
1.6* 2.2* 0.7* 0.8
1.3-1.9 1.7-2.8 0.6-0.9 0.6-1.0
2.0* 3.9* 0.5* 0.9
1.6-2.5 2.9-5.1 0.4-0.7 0.7-1.3
1.1 1.0 1.0 1.5*
0.9-1.3 0.8-1.2 0.8-1.3 1.2-2.0
0.8
0.6-1.1
2.5*
1.7-3.7
1.0
0.8-1.4
1.5*
1.1-2.0
2.5*
1.9-3.2
0.7* 0.4*
0.5-0.9 0.3-0.6
2.3* 1.6*
1.6-3.4 1.1-2.3
0.9 0.8
0.7-1.2 0.6-1.1
1.2 0.7
0.8-1.6 0.5-1.0
2.4* 0.7*
1.8-3.1 0.5-1.0
0.5*
0.4-0.8
0.6*
0.4-0.7
1.1
0.8-1.6
1.7*
1.2-2.4
1.9*
1.4-2.5
0.4*
0.2-0.7
0.7*
0.5-1.0
1.0
0.7-1.5
0.8
0.5-1.4
1.1
0.7-1.7
0.7
0.4-1.1
2.2*
1 2-3.8
1.1
0.7-1.6
0.6
0.3-1.1
0.9
0.6-1.5
(17 = 1 2 7 )
Patella (n = 110)
• Significantly (p < 0.05) different from 1. t Adjusted by Poisson regression for race, sex, age, and nursing home residence; the reference group is whites for race, males for sex, 65-74 years for age, and those not in a nursing home for residence. X RR, relative risk; Cl, confidence interval
tionally considered minimal to moderate (table 3). This included 82 percent of all fractures for white males, 73 percent for black males, 89 percent for white females, and 84 percent for black females. Between 52 percent (tibia/fibula) and 95 percent (hip) of specific fracture types were due to falls to the ground that occurred while the person was standing or sitting or transferring from one position to another (table 3). Most of these were falls from the same level or falls covering a short distance such as a step or curb. Other circumstances included: being caught between two objects or striking or being struck by an object (2 percent); greater degrees of trauma (8 percent), predominantly motor vehicle crashes, but also including assault and falls from greater heights; and spontaneous fractures (3 percent), that is, all those with no known associated trauma.
DISCUSSION
In this large retrospective cohort study of fractures in elderly Medicaid enrollees, the rate of all fractures in blacks was 40 percent of that of whites, after controlling for age, sex, and nursing homes status, and was consistently lower among blacks within the subgroups defined by these factors. We considered whether differential misclassification of fractures by race or differential selection of fracture-prone patients into the Medicaid program by race could have accounted for these findings. Since we used a computerized algorithm to identify fractures, it is likely that there was some misclassification of fractures. However, because of the high sensitivity and predictive value of the algorithm for most fractures (9), it is unlikely that the rates reported here err by more than 10 percent
1382
Griffin et al.
Male
Female
Male
Female
800-
10 "
30 -
Femoral Shad
20 10 -
30 •
Tbia/Fbula
20 -
CO CD >
10 -
£ o o o o
30 • Foot 20 • 10 •
30 -
I
Skull/Face
20 -
3
10 , 30 •
a
a
Clavide/Scapula
20 • 10
J-^J: 30 -
Patella
20 10
65-74 75^4 > 8 5
65-74 75-84
Age
2:85 Whit*
65-74 75-84 > 8 5 o--a Black
65-74 75-84 > 8 5
Age
FIGURE 1. Age- and sex- specific annual incidence (per 10,000 person-years) of first fracture, by site, among white (•) and black (•) Medicaid enrollees aged 65 years or more in Tennessee, 1987-1989.
Black-White Differences in Fracture Rates
1383
TABLE 3. Circumstances of fracture (%) for 1,048 Tennessee Medicaid enrollees aged 65 years or more whose medical records were reviewed, by site Fall with minimal/ moderate trauma
Other trauma
Total
Same level
Bed/chair/ commode
Any (n = 1,048)
87
75
11
2
8
3
Hip (n = 451) Radius/ulna (n = 119) Rib/sternum (n = 72) Humerus (n = 78) Pelvis (n = 51) Ankle (n = 56) Hand (n = 26) Femoral shaft (n = 35) Tibia/fibula (n = 25) Foot (n = 24) Skull/face (n = 28) Clavicle/scapula (n = 14) Patella (n = 9) Multiple sites (n = 60)
95 90
82 83
13 7
0 3
3 7
2 1
79
69
10
3
11
7
87 94 85 70 75 52 58 75 92
74 86 80' 62 49 40 54 43 71 78 60
13 8 5 8 26 12 4 32 21 11 5
1 0 2
5 6 9 0 9 28 13 25 7 0
6 0 4 0 17 20 0 0 0 11 2
89 65
for all fractures or for most individual fracture sites. In addition, we found that the sensitivity and predictive value of the algorithm were not influenced by age, sex, race, or nursing home status (9), so the differences in rates by age, sex, and race are unlikely to have been caused by misclassification. Elderly persons enrolled in the Medicaid program qualify because of poverty and/or medical illness, and in Tennessee, they represent only about 16 percent of the state's elderly population. Medicaid enrollees have higher proportions of women (77 percent), persons aged 85 years or more (19 percent), and nursing home residents (24 percent) than the general Tennessee population aged 65 years or more (16). Blacks comprised about 28 percent of our study population, compared with about 14 percent of those aged 65 years or more in the state of Tennessee (16). These particular demographic characteristics may influence race- and sexspecific rates if conditions associated with Medicaid enrollment influence fracture risk. Fracture rates in this Medicaid population are higher than those reported for other populations. In a study of all fall-related injuries among elderly persons in a predominately white population in South Miami Beach, Florida, which had demographics similar to
Caught/ struck
31
0 0 29 0 0 0 0
Greater trauma
Spontaneous fracture or cause unknown
33
the white Tennessee Medicaid population (63 percent women, 22 percent aged 85 years or more), the incidence of all nonskull fractures was 321 per 10,000 person-years (17) compared with a rate of 413 nonskull, nonvertebral fractures for the white elderly Medicaid enrollees in this study—a 30 percent rate increase. Hip fracture rates in this Medicaid population are also higher than those reported for other populations (2-7); ageand sex-adjusted rates were 70 percent and 40 percent higher than those previously reported for US whites and blacks, respectively (3). The differences between hip fracture rates among persons enrolled in Medicaid and other populations diminished with age, such that for black and white women aged 85 years or more, hip fracture incidence rates were nearly identical to those for US black and white women, respectively (3). Since illness is one criterion for Medicaid eligibility, Medicaid patients are likely to be sicker than their non-Medicaid counterparts. It is possible that there is differential selection of persons into Medicaid by race, such that white Medicaid enrollees are sicker or more fracture-prone than black enrollees. This type of selection bias could account for the racial differences in rates that we observed. However, the similarity of hip frac-
1384
Griffin et al.
ture rates in Medicaid enrollees aged 85 years or more with those of the general US population for both blacks and whites (3) suggests that these older enrollees may be similar to their non-Medicaid counterparts in terms of fracture risk. The racial differences in fracture rates persisted in this oldest age group. In addition, the consistency of these findings with other data showing similar racial differences in hip fracture rates (I, 3-6) argues against the large racial differences found in this population being due only to differential enrollment of fractureprone whites in the Medicaid program. The reasons for the lower fracture rates in blacks in this population are unknown. However, consistent racial differences in rates for fractures at all sites and for all ages studied suggest a common factor(s) underlying these differences. Because our data suggest that nearly 90 percent of these fractures resulted from a fall associated with minimal to moderate trauma, the most probable explanations for the observed lower rates in blacks are a lower risk of falling and/or increased bone strength (18). Although there are only limited data comparing fall rates in blacks and whites (19), there is considerable evidence that bone mass is higher in American blacks than in whites (20-22). Bone mineral density of the hip (20), radius (20, 21), and spine (20, 21) is higher in black women than in white women, after adjustment for age and body mass. There is some evidence that the rate of bone remodeling in blacks is lower than that in whites (22), which may protect blacks from age-related bone loss. Hip fractures accounted for only 36 percent of all nonvertebral fractures in this study. Although these fractures are more numerous and result in higher morbidity and costs than other types of fractures, when the data are considered together it is clear that other types of fractures contribute significantly to morbidity and health care costs (23). Despite the finding that fracture rates in blacks are close to half of those in whites, fall-related fractures remain a significant problem for blacks as well as whites. In our population, nearly 2 percent of black Med-
icaid enrollees sustained at least one nonvertebral fracture per year. Detailed studies are needed to elucidate the factors that underlie these racial differences in fracture incidence, including comparative studies of determinants of bone mass, fall risk, and fall characteristics. The public health significance of this line of research is underscored by the observation that reducing fracture rates among whites to the rate for blacks would have an effect in women as dramatic as that envisioned with long term estrogen replacement therapy (24). If the relevant mechanisms could be identified, fracture rates in blacks might be reduced even further.
REFERENCES 1. Melton LJ III. Differing patterns of osteoporosis across the world. In: Chestnut CH. ed. New dimensions in osteoporosis in the 1990s. Hong Kong: Excerpta Medica Asia, 1991:13-18. 2. Kellie SE, Brody JA. Sex-specific and race-specific hip fracture rates. Am J Public Health 1990:80: 326-8. 3. Rodriguez JG, Sattin RW, Waxweiler RJ. Incidence of hip fractures, United States. 1970-83. Am JPrevMed 1989.5:175-81. 4. Farmer ME, White LR, Brody JA. et al. Race and sex differences in hip fracture incidence. Am J Public Health 1984:74:1374-80. 5. Silverman SL, Madison RE. Decreased incidence of hip fracture in Hispanics, Asians, and blacks: California hospital discharge data. Am J Public Health 1988:78:1482-3. 6. Bauer RL. Ethnic differences in hip fracture: a reduced incidence in Mexican Americans. Am J Epidemiol 1988; 127:145-9. 7. Garraway WM, Stauffer RN. Kurland LT, et al. Limb fractures in a defined population. II. Orthopedic treatment and utilization of health care. MayoClin Proc 1979:54:708-13. 8. Melton LJ III. The second fifty years: promoting health and preventing disability. In: Berg RL, Cassells JS, eds. Osteoporosis. Washington, DC: National Academy Press, National Academy of Sciences, 1990:76-100. 9. Ray WA, Griffin MR, Fought RL, et al. Identification of fractures from computerized Medicare files. J Clin Epidemiol 1992:45:703-14.. 10. Ray WA. Griffin MR. Use of Medicaid data for pharmacoepidemiology. Am J Epidemiol 1989; 129:837-49. 11. Fanta CM, Finkel AJ, KJrschner CG, et al. Physicians' current procedural terminology. 4th ed. Chicago, IL: American Medical Association, 1992. 12. US Department of Health and Human Services. International Classification of Diseases, Ninth Re-
Black-White Differences in Fracture Rates
13. 14. 15. 16. 17.
18. 19.
vision, Clinical Modification. 2nd ed. Washington, DOUSGPO, 1980. Hollmann FW. United States population estimates, by age, sex, race, and Hispanic origin: 1980 to 1988. Curr Pop Rep l990;l045:4l. McCullagh P, Nelder JA. Generalized linear models. 2nd ed. New York: Chapman and Hall Ltd, 1989. Payne CD. Generalized Linear Interactive Modeling: the GLIM system. Oxford, England: Royal Statistical Society, 1986. Tennessee Statistical Abstracts 1989. 11th ed. Knoxville, TN: Center for Business and Economic Research, 1989. Sattin RW, Huber DAL, DeVito CA, et al. The incidence of fall injury events among the elderly in a defined population. Am J Epidemiol 1990; 131: 1028-37. Melton JL III, Wahner HW, Richelson LS, et al. Osteoporosis and the risk of hip fracture. Am J Epidemiol 1986; 124:254-61. Nevitt MC, Cummings SR, Kidd S, et al. Risk
20.
21.
22. 23.
24.
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factors for recurrent nonsyncopal falls: a prospective study. JAMA 1989,261:2663-8. Liel Y, Edwards J, Shary J, et al. The effects of race and body habitus on bone mineral density of the radius, hip, and spine in premenopausal women. J Clin Endocrinol Metab 1988,66:1247-50. Luckey MM, Meier DE, Mandeli JP, et al. Radial and vertebral bone density in white and black women: evidence for racial differences in premenopausal bone homeostasis. J Clin Endocrinol Metab 1989,69:762-70. Weinstein RS, Bell NH. Diminished rates of bone formation in normal black adults. N Engl J Med 1988,319:1698-1700. Melton LJ 111. Epidemiology of fractures. In: Riggs BL, Melton LJ III, eds. Osteoporosis: etiology, diagnosis, and management. New York: Raven Press, 1988:133-54. Weiss NS, Ure CL, Ballard JH, et al. Decreased risk of fractures of the hip and lower forearm with postmenopausal use of estrogen. N Engl J Med 198O;3O3:1195-8.
Vol. 136, No. 11 Printed in U.S.A.
Black-White Differences in Fracture Rates
Marie R. Griffin,1 Wayne A. Ray,1 Randy L. Fought,1 and L. Joseph Melton III2
To compare the incidence of all nonvertebral fractures between elderly blacks and whites, the authors conducted a retrospective cohort study among Tennessee Medicaid enrollees aged 65 years or more from 1987 through 1989. A previously validated computer algorithm identified 6,802 persons of black or white race with 7,645 new nonvertebral fractures. The incidence of all nonvertebral fractures in blacks was only half of that in whites. This finding persisted after the authors controlled for sex, age, and nursing home residence (relative risk = 0.4, 95% confidence interval 0.4-0.5). Rates were consistently lower among blacks within subgroups defined by these factors and for each of the 13 different fracture sites examined. The magnitude of the difference between blacks and whites in rates of all fractures combined and most site-specific fractures is similar to that previously reported for hip fractures. These consistent racial differences suggest a common underlying factor(s). Am J Epidemiol 1992;136: 1378-85. aged; blacks; fractures; incidence; racial stocks; retrospective studies; whites
The incidence of hip fracture is higher in whites than in blacks (1). Most studies have found rates in white women to be 2-3 times those in black women, while rates in white men are 1-2 times those in black men (26). These data are available because hip fractures are relatively common in the elderly, are easily diagnosed, and nearly always result in hospitalization, thus permitting their study with computerized hospital discharge Received for publication February 10,1992, and in final form May 19, 1992. 1 Department of Preventive Medicine, Vanderbilt University School of Medicine, Nashville, TN. 2 Section of Clinical Epidemiology, Mayo Clinic and Mayo Foundation, Rochester, MN. Reprint requests to Dr. Marie R. Griffin, Department of Preventive Medicine, Vanderbilt University School of Medicine, A-1124 MCN, 1161 21st Avenue, Nashville, TN 37232-2637. This research was supported by grants from the Centers for Disease Control (R49/CCR403562-02-1) and the Food and Drug Administration (FD-U-000073) Dr. Marie Griffin is a Burroughs Wellcome Scholar in pharmacoepidemiology. The authors gratefully acknowledge the assistance of Susan Patterson, Janet Higdon, and De'Siree' MorganLyons with manuscript preparation
data. However, such data are inadequate for identifying fractures at other skeletal sites, which often do not result in hospital admission (7). As a consequence, these other fractures have been much less studied, even though they are associated with substantial disability and cost and together outnumber hip fractures (8). Little is known about racial differences in rates of these other fractures. To overcome this problem, we developed and validated a method of fracture identification using computerized inpatient and outpatient Medicaid and Medicare claim files which has a positive predictive value of 94 percent and an estimated sensitivity of 91 percent for all treated fractures combined (9). We thus were able to study the epidemiology of all nonvertebral fractures in the elderly Tennessee Medicaid population from 1987 through 1989. MATERIALS AND METHODS Sources of data
The study population was identified using the Tennessee Medicaid enrollment file,
1378
Black-White Differences in Fracture Rates
which includes personal identifiers and information on demographic characteristics, periods of enrollment, and (through linkage with death certificates) dates of death and coded underlying causes of death (10). Fractures were identified using Medicare (for those Medicaid recipients also enrolled in Medicare) and Medicaid claim files indicating a diagnosis of fracture coded using the International Classification of Diseases, Ninth Revision, Clinical Modification (II) or treatment for fracture coded using the Physicians' Current Procedural Terminology, Fourth Edition (12) (9, 10). Cohort definition
We studied the incidence of new fractures in the population of Tennessee Medicaid enrollees aged 65 years or more from 1987 through 1989. For each individual, persontime began during the study years when all of the following three criteria were met: attainment of age 65 years, enrollment in Medicaid for at least 365 days (to exclude persons enrolled in Medicaid because of expenses associated with a fracture), and absence of a billing code indicating a fracture in the preceding 31 days (to exclude encounters associated with fracture follow-up care). Person-time at risk for each type of fracture ended on the first of the following dates: first fracture of that type, loss of Medicaid enrollment, death, or the end of the study period (December 31, 1989). Fracture ascertainment
We used a previously developed computer algorithm to identify new fractures (9). To develop the algorithm, we identified 3,086 possible nonvertebral fractures during 1987 among persons aged 65 years or more based upon the computerized diagnostic and procedure codes. Vertebral fractures were excluded because they are often asymptomatic and frequently do not result in a medical encounter. Review of medical records for a sample of 1,440 of^the 3,086 possible fractures allowed us to develop a computer algorithm that identified new fractures with an estimated positive predictive value of 94
1379
percent and sensitivity of 91 percent. The estimated positive predictive value and sensitivity of the computer algorithm for identifying fractures at 13 specific sites (in order of their frequency) are as follows: for the hip, the positive predictive value was 98 percent and sensitivity was 97 percent; for the radius/ulna, 96 percent and 93 percent; for the humerus, 95 percent and 90 percent; ribs/sternum, 84 percent and 82 percent; pelvis, 93 percent and 89 percent; ankle, 96 percent and 78 percent; femoral shaft, 87 percent and 75 percent; hand, 86 percent and 87 percent; tibia/fibula, 79 percent and 87 percent; skull/face, 89 percent and 97 percent; foot, 95 percent and 90 percent; clavicle/scapula, 86 percent and 91 percent; and patella, 82 percent and 100 percent. For the present study, we identified the first fracture at each site for all cohort members during the study period, exclusive of vertebral fractures. Analysis
Unadjusted rates for site-specific fractures and all nonvertebral fractures were calculated by dividing the number of fractures by person-time with stratification by age, sex, and race. Summary age- and sex-adjusted rates for blacks and whites were calculated using the population structure of US whites in 1988 (13). The effects of age, sex, race, nursing home status, month (to evaluate seasonal variation), calendar year (to evaluate temporal trends), and residence (urban, suburban, or rural) on site-specific fracture rates were estimated from Poisson regression models (14) using the GLIM program (15). Month, calendar year, and residence did not influence fracture rates; the simpler model which excluded those terms gave similar results, and those results are presented here. To examine the distribution of circumstances of fracture, we used data from the 1,207 patients with confirmed fractures for whom medical records were reviewed for the validation study (9). Patients were classified by site of fracture if there was a single fracture; otherwise, they were classified as having multiple fractures.
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RESULTS
During the three study years 1987-1989, 7,424 Tennessee Medicaid enrollees aged 65 years or more had one or more nonvertebral fractures identified by the computer algorithm. This study was confined to the 6,802 persons (92 percent) of white or black race, with a total of 7,645 fractures. The incidence of new nonvertebral fractures was lower for blacks than for whites within each age and sex group (table 1), with ratios ranging from 0.6:1 to 0.4:1. The overall ratio of age- and sex-adjusted rates was 0.5:1. Within each racial group, incidence of fracture increased with age such that, among those aged 85 years or more, 4.6 percent of white males, 2.1 percent of black males, 7.0 percent of white females, and 2.8 percent of black females in this population sustained at least one nonvertebral fracture annually. The most common fractures were those of the hip, which made up 36 percent of all fractures in this age group, the radius/ulna (13 percent), the rib/sternum (11 percent), the humerus (9 percent), and the pelvis (6 percent). The other sites each accounted for less than 5 percent of all fractures (table 2). Rates of fracture occurrence varied markedly by fracture site, age, and sex (figure 1). However, for each fracture site, age- and sexspecific rates were lower in blacks than in whites. In an analysis which controlled for sex,
age, and nursing home residence, overall fracture rates in blacks were 40 percent of those of whites (relative risk = 0.4, 95 percent confidence interval 0.4-0.5) (table 2). In addition, fracture rates were lower in blacks than in whites for each fracture site, and in most instances, the differences in rates were statistically significant (table 2). After we controlled for race, age, and nursing home residence, fracture rates were significantly greater at most skeletal sites in women than in men (table 2). Men had greater rates for fractures of the skull and face, chest (rib/sternum or clavicle/scapula), and hand, although the latter difference was not statistically significant. After we controlled for race and sex, fracture rates increased with age at most sites (table 2). Only ankle fractures were significantly more common among younger individuals. The overall incidence of fractures was higher among nursing home residents, primarily because of significantly higher rates of hip, hand, femoral shaft, tibia/fibula, and skull/face fractures. However, fractures of the radius/ ulna, rib/sternum, and foot were significantly lower among nursing home residents. Of the sample of 1,207 persons with fractures for whom the medical record was reviewed, 1,048 (87 percent) were of white or black race and had the circumstances of the fracture recorded in the medical record. Eighty-seven percent of all fractures were due to falls associated with trauma conven-
TABLE 1. Age-, race-, and sex-specific and age- and sex-adjusted annual incidence rates (per 10,000 person-years) of first nonvertebral fracture among Tennessee Medicaid enrollees aged 65 years or more, 1987-1989 Whites (years)
Person-years
No of fractures
Blacks Rate
Person-years
No. of fractures
Rate
Male 65-74 75-84 >85
14,021 13,756 5,064
348 472 231
248 343 456
5,436 5,322 2,178
78 79 46
143 148 211
Female 65-74 75-84 >85
40,581 41,882 22,304
1,238 2,029 1,554
305 484 697
17,052 15,630 7,447
255 264 208
150 169 279
137,608
5,872
362
53,065
930
163
Adjusted total
Black-White Differences in Fracture Rates
1381
TABLE 2. Adjusted relative riskt of fractures at various sites, by race, sex, age, and nursing home residence, among Tennessee Medicaid enrollees aged 65 years or more, 1987-1989 Black race
Female sex
Age 75-84 years
Age >85 years
Site
RRt
95% C\%
RR
Nursing home resident
95% Cl
RR
95% Cl
RR
95% Cl
RR
95% Cl
1.3-1.5
1.9*
1.8-2.0
1.3*
1.2-1.4
Any (n = 6,802)
0.4*
0.4-0.5
1.3*
1.3-1.4
1.4*
Hip (n = 2,750) Radius/ulna (n = 1,004) Rib/sternum (n = 858) Humerus (n = 659) Pelvis (n = 443) Ankle (n = 368) Hand (n = 314) Femoral shaft (n = 275) Tibia/fibula (n = 274) Foot(n = 241) Skull/face (n = 222) Clavicle/scapula
0.4*
0.4-0.5
1.2*
1.1-1.3
2.2*
2.0-2.5
3.2*
2.8-3.5
1.8*
1.6-1.9
0.3*
0.3-0.4
2.5*
2.1-3.1
1.2*
1.0-1.3
1.2
1.0-1.4
0.8*
0.7-0.9
0.4*
0.3-0.4
0.8*
0.7-0.9
1.4*
1.2-1.6
1.9*
1.6-2.3
0.7*
0.6-0.9
0.3* 0.3* 0.7* 0.6*
0.2-0.4 0.2-0.4 0.5-0.9 0.4-0.8
1.7* 2.6* 2.4* 0.9
1.4-2.1 1.9-3.5 1.8-3.3 0.7-1.1
1.6* 2.2* 0.7* 0.8
1.3-1.9 1.7-2.8 0.6-0.9 0.6-1.0
2.0* 3.9* 0.5* 0.9
1.6-2.5 2.9-5.1 0.4-0.7 0.7-1.3
1.1 1.0 1.0 1.5*
0.9-1.3 0.8-1.2 0.8-1.3 1.2-2.0
0.8
0.6-1.1
2.5*
1.7-3.7
1.0
0.8-1.4
1.5*
1.1-2.0
2.5*
1.9-3.2
0.7* 0.4*
0.5-0.9 0.3-0.6
2.3* 1.6*
1.6-3.4 1.1-2.3
0.9 0.8
0.7-1.2 0.6-1.1
1.2 0.7
0.8-1.6 0.5-1.0
2.4* 0.7*
1.8-3.1 0.5-1.0
0.5*
0.4-0.8
0.6*
0.4-0.7
1.1
0.8-1.6
1.7*
1.2-2.4
1.9*
1.4-2.5
0.4*
0.2-0.7
0.7*
0.5-1.0
1.0
0.7-1.5
0.8
0.5-1.4
1.1
0.7-1.7
0.7
0.4-1.1
2.2*
1 2-3.8
1.1
0.7-1.6
0.6
0.3-1.1
0.9
0.6-1.5
(17 = 1 2 7 )
Patella (n = 110)
• Significantly (p < 0.05) different from 1. t Adjusted by Poisson regression for race, sex, age, and nursing home residence; the reference group is whites for race, males for sex, 65-74 years for age, and those not in a nursing home for residence. X RR, relative risk; Cl, confidence interval
tionally considered minimal to moderate (table 3). This included 82 percent of all fractures for white males, 73 percent for black males, 89 percent for white females, and 84 percent for black females. Between 52 percent (tibia/fibula) and 95 percent (hip) of specific fracture types were due to falls to the ground that occurred while the person was standing or sitting or transferring from one position to another (table 3). Most of these were falls from the same level or falls covering a short distance such as a step or curb. Other circumstances included: being caught between two objects or striking or being struck by an object (2 percent); greater degrees of trauma (8 percent), predominantly motor vehicle crashes, but also including assault and falls from greater heights; and spontaneous fractures (3 percent), that is, all those with no known associated trauma.
DISCUSSION
In this large retrospective cohort study of fractures in elderly Medicaid enrollees, the rate of all fractures in blacks was 40 percent of that of whites, after controlling for age, sex, and nursing homes status, and was consistently lower among blacks within the subgroups defined by these factors. We considered whether differential misclassification of fractures by race or differential selection of fracture-prone patients into the Medicaid program by race could have accounted for these findings. Since we used a computerized algorithm to identify fractures, it is likely that there was some misclassification of fractures. However, because of the high sensitivity and predictive value of the algorithm for most fractures (9), it is unlikely that the rates reported here err by more than 10 percent
1382
Griffin et al.
Male
Female
Male
Female
800-
10 "
30 -
Femoral Shad
20 10 -
30 •
Tbia/Fbula
20 -
CO CD >
10 -
£ o o o o
30 • Foot 20 • 10 •
30 -
I
Skull/Face
20 -
3
10 , 30 •
a
a
Clavide/Scapula
20 • 10
J-^J: 30 -
Patella
20 10
65-74 75^4 > 8 5
65-74 75-84
Age
2:85 Whit*
65-74 75-84 > 8 5 o--a Black
65-74 75-84 > 8 5
Age
FIGURE 1. Age- and sex- specific annual incidence (per 10,000 person-years) of first fracture, by site, among white (•) and black (•) Medicaid enrollees aged 65 years or more in Tennessee, 1987-1989.
Black-White Differences in Fracture Rates
1383
TABLE 3. Circumstances of fracture (%) for 1,048 Tennessee Medicaid enrollees aged 65 years or more whose medical records were reviewed, by site Fall with minimal/ moderate trauma
Other trauma
Total
Same level
Bed/chair/ commode
Any (n = 1,048)
87
75
11
2
8
3
Hip (n = 451) Radius/ulna (n = 119) Rib/sternum (n = 72) Humerus (n = 78) Pelvis (n = 51) Ankle (n = 56) Hand (n = 26) Femoral shaft (n = 35) Tibia/fibula (n = 25) Foot (n = 24) Skull/face (n = 28) Clavicle/scapula (n = 14) Patella (n = 9) Multiple sites (n = 60)
95 90
82 83
13 7
0 3
3 7
2 1
79
69
10
3
11
7
87 94 85 70 75 52 58 75 92
74 86 80' 62 49 40 54 43 71 78 60
13 8 5 8 26 12 4 32 21 11 5
1 0 2
5 6 9 0 9 28 13 25 7 0
6 0 4 0 17 20 0 0 0 11 2
89 65
for all fractures or for most individual fracture sites. In addition, we found that the sensitivity and predictive value of the algorithm were not influenced by age, sex, race, or nursing home status (9), so the differences in rates by age, sex, and race are unlikely to have been caused by misclassification. Elderly persons enrolled in the Medicaid program qualify because of poverty and/or medical illness, and in Tennessee, they represent only about 16 percent of the state's elderly population. Medicaid enrollees have higher proportions of women (77 percent), persons aged 85 years or more (19 percent), and nursing home residents (24 percent) than the general Tennessee population aged 65 years or more (16). Blacks comprised about 28 percent of our study population, compared with about 14 percent of those aged 65 years or more in the state of Tennessee (16). These particular demographic characteristics may influence race- and sexspecific rates if conditions associated with Medicaid enrollment influence fracture risk. Fracture rates in this Medicaid population are higher than those reported for other populations. In a study of all fall-related injuries among elderly persons in a predominately white population in South Miami Beach, Florida, which had demographics similar to
Caught/ struck
31
0 0 29 0 0 0 0
Greater trauma
Spontaneous fracture or cause unknown
33
the white Tennessee Medicaid population (63 percent women, 22 percent aged 85 years or more), the incidence of all nonskull fractures was 321 per 10,000 person-years (17) compared with a rate of 413 nonskull, nonvertebral fractures for the white elderly Medicaid enrollees in this study—a 30 percent rate increase. Hip fracture rates in this Medicaid population are also higher than those reported for other populations (2-7); ageand sex-adjusted rates were 70 percent and 40 percent higher than those previously reported for US whites and blacks, respectively (3). The differences between hip fracture rates among persons enrolled in Medicaid and other populations diminished with age, such that for black and white women aged 85 years or more, hip fracture incidence rates were nearly identical to those for US black and white women, respectively (3). Since illness is one criterion for Medicaid eligibility, Medicaid patients are likely to be sicker than their non-Medicaid counterparts. It is possible that there is differential selection of persons into Medicaid by race, such that white Medicaid enrollees are sicker or more fracture-prone than black enrollees. This type of selection bias could account for the racial differences in rates that we observed. However, the similarity of hip frac-
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Griffin et al.
ture rates in Medicaid enrollees aged 85 years or more with those of the general US population for both blacks and whites (3) suggests that these older enrollees may be similar to their non-Medicaid counterparts in terms of fracture risk. The racial differences in fracture rates persisted in this oldest age group. In addition, the consistency of these findings with other data showing similar racial differences in hip fracture rates (I, 3-6) argues against the large racial differences found in this population being due only to differential enrollment of fractureprone whites in the Medicaid program. The reasons for the lower fracture rates in blacks in this population are unknown. However, consistent racial differences in rates for fractures at all sites and for all ages studied suggest a common factor(s) underlying these differences. Because our data suggest that nearly 90 percent of these fractures resulted from a fall associated with minimal to moderate trauma, the most probable explanations for the observed lower rates in blacks are a lower risk of falling and/or increased bone strength (18). Although there are only limited data comparing fall rates in blacks and whites (19), there is considerable evidence that bone mass is higher in American blacks than in whites (20-22). Bone mineral density of the hip (20), radius (20, 21), and spine (20, 21) is higher in black women than in white women, after adjustment for age and body mass. There is some evidence that the rate of bone remodeling in blacks is lower than that in whites (22), which may protect blacks from age-related bone loss. Hip fractures accounted for only 36 percent of all nonvertebral fractures in this study. Although these fractures are more numerous and result in higher morbidity and costs than other types of fractures, when the data are considered together it is clear that other types of fractures contribute significantly to morbidity and health care costs (23). Despite the finding that fracture rates in blacks are close to half of those in whites, fall-related fractures remain a significant problem for blacks as well as whites. In our population, nearly 2 percent of black Med-
icaid enrollees sustained at least one nonvertebral fracture per year. Detailed studies are needed to elucidate the factors that underlie these racial differences in fracture incidence, including comparative studies of determinants of bone mass, fall risk, and fall characteristics. The public health significance of this line of research is underscored by the observation that reducing fracture rates among whites to the rate for blacks would have an effect in women as dramatic as that envisioned with long term estrogen replacement therapy (24). If the relevant mechanisms could be identified, fracture rates in blacks might be reduced even further.
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vision, Clinical Modification. 2nd ed. Washington, DOUSGPO, 1980. Hollmann FW. United States population estimates, by age, sex, race, and Hispanic origin: 1980 to 1988. Curr Pop Rep l990;l045:4l. McCullagh P, Nelder JA. Generalized linear models. 2nd ed. New York: Chapman and Hall Ltd, 1989. Payne CD. Generalized Linear Interactive Modeling: the GLIM system. Oxford, England: Royal Statistical Society, 1986. Tennessee Statistical Abstracts 1989. 11th ed. Knoxville, TN: Center for Business and Economic Research, 1989. Sattin RW, Huber DAL, DeVito CA, et al. The incidence of fall injury events among the elderly in a defined population. Am J Epidemiol 1990; 131: 1028-37. Melton JL III, Wahner HW, Richelson LS, et al. Osteoporosis and the risk of hip fracture. Am J Epidemiol 1986; 124:254-61. Nevitt MC, Cummings SR, Kidd S, et al. Risk
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factors for recurrent nonsyncopal falls: a prospective study. JAMA 1989,261:2663-8. Liel Y, Edwards J, Shary J, et al. The effects of race and body habitus on bone mineral density of the radius, hip, and spine in premenopausal women. J Clin Endocrinol Metab 1988,66:1247-50. Luckey MM, Meier DE, Mandeli JP, et al. Radial and vertebral bone density in white and black women: evidence for racial differences in premenopausal bone homeostasis. J Clin Endocrinol Metab 1989,69:762-70. Weinstein RS, Bell NH. Diminished rates of bone formation in normal black adults. N Engl J Med 1988,319:1698-1700. Melton LJ 111. Epidemiology of fractures. In: Riggs BL, Melton LJ III, eds. Osteoporosis: etiology, diagnosis, and management. New York: Raven Press, 1988:133-54. Weiss NS, Ure CL, Ballard JH, et al. Decreased risk of fractures of the hip and lower forearm with postmenopausal use of estrogen. N Engl J Med 198O;3O3:1195-8.
