Jan 2, 1985 - with hip fractures to a Texas hospital was compared with that of age-matched ... hospital in San Antonio, Texas, between 1980 and 1984.9 We.
Risk of Postmenopausal Hip Fracture in Mexican American Women RICHARD L. BAUER, MD, MSc, ANDREW K. DIEHL, MD, MSc, SARA A. BARTON, MS, JEAN BRENDER, RN, PHD, AND RICHARD A. DEYO, MD, MPH
____ TABLE 1-Ethnic Distributions of Hip Fracture Patients and Controls
Abstract: To assess the risk of hip fracture in Mexican Americans, the ethnicity of 80 women aged 50 years and over admitted with hip fractures to a Texas hospital was compared with that of age-matched women hospitalized for other reasons. The risk of fracture for Mexican Americans was only 35 per cent that of Whites (95% CI = 19 per cent, 65 per cent). This finding was confirmed in a chart survey performed in a second hospital population. These results suggest that Mexican American women may receive less potential benefit from preventive measures for hip fracture than Whites. (Am J Public Health 1986; 76:1020-1021.)
Introduction The risk of postmenopausal hip fracture varies widely among racial groups.'-5 In the United States, Blacks have low rates of hip fracture relative to Whites. 8 Although Mexican Americans are a large and growing minority in the United States, their risk of hip fracture has not been previously described. This study examines the risk of hip fracture in Mexican American women relative to women of other ethnic groups using two independent data sets. Methods Case Control Study
Cases and controls were selected from women inpatients aged 50 years and older admitted to a large teaching hospital in San Antonio, Texas, between 1980 and 1984.9 We located charts of 99 of 101 femoral fracture patients (ICD codes 820-821) identified in the hospital discharge log. Thirteen patients with subtrochanteric fractures, four with prior hip fractures, and two lacking x-ray reports were excluded. ' For each case, two controls matched for age (within five years), sex, and admission date were selected from the admission log. Patients with a prior history of hip fracture were excluded as controls. Thirty per cent of controls were admitted for cardiovascular disease, 19 per cent for cancer, 20 per cent for surgical procedures, and 6 per cent for orthopedic problems other than hip fracture. No other diagnosis made up more than 5 per cent of controls. Physicians' admission notes and the hospital data base were reviewed to determine each subject's ethnicity (Mexican American, Black, White, and other). The patient's surname and maiden name were also compared with the 1980 list of Spanish surnames published by the US Census Bureau. " Address reprint requests to Richard L. Bauer, MD, MSc, Division of General Medicine, Department of Medicine, University of Texas Health Science Center at San Antonio, San Antonio, TX 78284 (Dr. Bauer is a Milbank scholar in epidemiology). Drs. Diehl and Deyo are also with the same department at the University; Ms. Barton is with the Center for Demographic and Population Genetics, University of Texas Health Science Center at Houston; Ms. Brender is a research health scientist at Audie Murphy Veterans Administration Hospital, San Antonio. This paper, submitted to the Journal June 13, 1985, was revised and accepted for publication January 2, 1985. © 1986 American Journal of Public Health 0090-0036/86$1.50
1 020
Ethnicity
Hip Fracture Patients N (%)
Controls N (%)
Mexican American White Black Other TOTAL
30 (37) 43 (54) 7 (9) 0 (0) 80 (100)
88 (55) 48 (30) 23 (14) 1 (1) 160 (100)
Physician assessment of ethnicity was used in these analyses because it was recorded in all charts and because it agreed closely with other methods of classification. Agreement between various methods of classifying ethnic group was tested using the kappa statistic."2 In all comparisons, agreement was very strong (physicians vs data base, kappa = 0.97; physicians vs surname, kappa = 0.94; physicians vs maiden name, kappa = 0.79). The odds ratios for hip fracture were determined using
the maximum likelihood method for matched data."' Confidence intervals were determined with Miettinen's test-based method.'4 Age-stratified analyses (by 10-year age intervals) were also performed.'3 15 Hospital Discharge Survey
To determine if the relation between Mexican American ethnicity and hip fracture holds for other populations, we analyzed data from a 1970-71 hospital discharge survey of 18 hospitals in eight rural southeast Texas counties.* Current and past discharges for hip fracture were identified for 2,075 randomly selected women (1768 Whites, 225 Blacks, and 82 Mexican Americans) aged 50 years and over. Ethnicity was assessed from chart entries. All femoral fractures (ICD 820-821) were counted in this analysis, as it was not possible to distinguish subtrochanteric from other femoral fractures. Summary odds ratios were determined after stratifying by 10-year age intervals. 13 15 Ninety-five per cent confidence intervals were calculated using Miettinen's test-based method. 14 Results Case Control Study
Mexican Americans and Blacks were less represented among hip fracture patients (mean age 73.2 years) than among controls (mean age 72.3 years) (Table 1). In the matched pairs analysis, the odds ratio of fracture for Mexican Americans as compared with Whites was 0.35 (95% CI, 0.19 to 0.65). The odds ratio for Blacks was 0.43 (95% CI, 0.16 to 1.18) as compared to Whites. An age-stratified analysis gave nearly identical estimates of risk, and the odds ratio did not vary much among age strata. To identify potential bias due to differing referral patterns for hip fracture patients and controls, we compared the estimated income and area of residence for both groups. Zip codes and *Barton SA, Seybold SV, Schull WJ: Man's burden of inherited disease and disability: eight counties in Texas. US-Mexico Border Health Association meeting, Monterrey, Nuevo Leon, Mexico, June 18, 1974.
AJPH August 1986, Vol. 76, No. 8
PUBLIC HEALTH BRIEFS TABLE 2-Prevalence of Hip Fracture In the 1970-71 HospIal Discharge Survey
Total number of women % Age >75 % of patients with hip fracture Age adjusted odds ratio (OR) 95% confidence intervals for OR
Whites
Mexican Americans
Blacks
1768 24.2 4.6
82 15.9 2.4 .77
225 31.1 1.3 .30
(.19-3.17)
(.10-.88)
-
income levels were similar within ethnic groups, suggesting that cases and controls came from similar populations.
fracture, is less common among Mexican Americans than Whites.'9' 20 While these environmental factors may be important, it is also possible that Mexican Americans have a greater bone mass than Whites. The increased bone mass of Blacks probably accounts for their decreased risk of fracture.2' While the reasons for lowered fracture risk among Mexican Americans remain unclear, this ethnic group does appear to enjoy relative protection. This observation may be clinically important in guiding prophylactic therapy.22 ACKNOWLEDGMENTS This research was presented in part at the national meeting of the American Federation for Clinical Research, Washington, DC, May 1985.
Hospital Discharge Survey
REFERENCES
The proportion of patients with hip fracture differed substantially between ethnic groups (Table 2). After adjustment for age, the odds ratio for hip fractures among Blacks as compared with Whites was 0.30 (95% CI, 0.10 to 0.88). The odds ratio for Mexican Americans as compared with Whites was also reduced (0.77) although the 95% confidence intervals on this value were quite wide (95% CI, 0.19 to 3.17). Discussion
The results of the case control study indicate a decreased risk of hip fracture in Mexican American and Black women in comparison with Whites. The low risk of hip fracture in Blacks is comparable with results of previous studies.A8 These similarities suggest that our study methods did not result in a biased comparison of Blacks with Whites, and tend to support the validity of our comparison of Mexican Americans with Whites. In the hospital discharge survey, the estimated risk of hip fracture among Mexican Americans was lower than for Whites although the wide confidence interval around this value indicates considerable imprecision. Our inability to distinguish subtrochanteric from other hip fractures may have reduced the observed association. It is unlikely that bias in the selection of study subjects in the case control study influenced our findings. Cases and controls were matched for age and sex, and all diagnoses were considered in the control group except for patients with a prior hip fracture. In addition, ethnic differences in referral patterns do not appear to account for the reduced risk in Mexican Americans. Other potential confounding variables were not examined in this study. Estrogen use and high calcium intake, both of which decrease the risk of hip fracture, are reported to be less frequent in Mexican Americans.'6 Controlling for these factors may further reduce the observed odds ratio for hip fractures in Mexican Americans. On the other hand, adjusting for obesity, which is more common in Mexican Americans, may increase the estimate of risk.'7' 18 In addition, smoking, which is associated with increased risk of hip
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