Trend of hip fracture incidence in Germany : a population-based study

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1 DOI /s ORIGINAL ARTICLE Trend of hip fracture incidence in Germany : a population-based study A. Icks & B. Haastert & M. Wildner & C. Becker & G. Meyer Received: 2 August 2007 / Accepted: 16 November 2007 # International Osteoporosis Foundation and National Osteoporosis Foundation 2007 Abstract Summary We analyzed hip fracture incidence trends in Germany , using national hospital discharge register. Crude incidences per 100,000 increased from (95% CI ) in 1995 to ( ) in Age-sex-adjusted annual incidence ratios A. Icks Faculty of Public Health, Department of Epidemiology and International Public Health, School of Public Health, Bielefeld University, Bielefeld, Germany A. Icks North-Rhine Westphalian Chamber of Physicians, Düsseldorf, Germany B. Haastert medistatistica, Neuenrade, Germany M. Wildner Bavarian Health and Food Safety Authority, Oberschleissheim, Germany C. Becker Center of Geriatrics, Robert Bosch Hospital, Stuttgart, Germany G. Meyer Institute of Public Health and Nursing Research, Bremen University, Bremen, Germany A. Icks (*) Faculty of Public Health, Bielefeld University, c/o North-Rhine Westphalian Chamber of Physicians, Tersteegenstr. 9, Düsseldorf, Germany dr.andrea.icks@aekno.de showed a statistically significant, but only slight increase (1.01, p<0.01), compared to higher rises in the past. Trends differed markedly with sex, age, and regions. Introduction Data concerning actual trends of the hip fracture incidence and differences for sex, age, and region are limited. We analyzed hip fracture incidence trends in Germany , using the national hospital discharge register. Crude incidences per 100,000 increased from (95% CI ) in 1995 to ( ) in Age-sex-adjusted annual incidence ratios showed a statistically significant, but only slight increase (1.01, p<0.01), compared to higher rises in the past. Trends differed markedly with sex, age, and regions. Methods Analysis of annual hip fracture incidences using the national hospital discharge register. Estimate of age-sexadjusted changes was found by using Poisson regression (incidence rate ratios, IRR). Results The number of patients with at least one hospital admission for hip fracture increased (1995: n=99,141; 2004: n=116,281). Crude incidences per 100,000 were (95% confidence interval ,9) and ( ), respectively. The age-sex-adjusted hip fracture incidence increased statistically significantly, but only slightly (IRR per year: 1.01; ; IRR : 1.05, p<0.01). In men aged 40 years or older, incidences increased. In women, there was a tendency of a decrease up to 74 years of age, but also a significant increase in higher age groups. In people 0-39 years, the incidence declined markedly (IRR , men 0.74; , women 0.62; , both p<0.01). The increase was significantly higher in Eastern compared to Western Germany (interaction: p=0.002), and differences between East and West decreased. Conclusions In contrast to earlier years, the hip fracture incidence in Germany increased only slightly,

2 with a decline in younger people, but increases in older ages, particularly in men. Regional differences decreased. Keywords Epidemiology. Hip fracture. Incidence. Population-based register study. Trend analysis Introduction The burden of hip fractures is well recognized. In addition to causing substantial health deterioration, hip fractures have a large economic effect due to the requirement of hospital and follow-up care [1, 2]. The incidence of hip fractures increases with age, and the total number of fractures is expected to rise due to population aging. This relates both to the relative proportion of the elderly within populations and an increase of the oldest old (double aging). Only a limited number of studies investigated actual trends of the hip fracture incidence. In contrast to earlier studies [3 5], only a few studies found an increase in the elderly even after age-adjustment [6, 7]. However, the majority of analyses found a leveling off or even a decrease of the age-adjusted hip fracture incidence [8 12]. Some studies found different trends for men and women and for various age groups [13 15]. Hip fracture incidence trends in younger people have not been evaluated. In Germany, the nationwide trend of hip fracture incidence is unknown so far, since data for Western Germany are available only for years after the mid-1990s. A former study evaluated the trend in Eastern Germany between 1971 and 1996 and found an age-adjusted annual rise of approximately 3%. Between 1990, the year of the reunification of Eastern and Western Germany, and 1996, the annual rise was even up to 6%. Interestingly, the hip fracture incidence in Western Germany in 1996 has been found to be significantly higher compared to Eastern Germany [4]. Thus, the aim of our study was (1) to analyze the secular trend of hip fracture in Germany from 1995 to 2004, using the national hospital discharge diagnosis registry, (2) to evaluate differences in trends for sex and age groups, and (3) to compare the actual situation and trends in Western and Eastern Germany. Methods Population and data We used data from the national hospital discharge diagnosis register (Krankenhausdiagnosestatistik). This register provides data on hospital discharges since 1993 and covers more than 99% of hospitals in Germany. Its validity has been proven in several studies [4]. Each hospital discharge is registered with date, age and sex of the patient, patient s residence, and diagnosis. Diagnoses are coded using the International Classification of Diseases (ICD). Hip fractures were counted by ICD 9 diagnosis 820 (up to 1999) and by ICD 10 diagnosis S72.0, S72.1, and S72.2. The accuracy of hip fracture coding has been verified [4]. A number of 1,515 cases were not available due to missing data (0.12% of the total of 1,213,820 cases). Population data were taken from official statistics (National Office of Statistics). Statistical analyses We estimated annual hip fracture incidences per 100,000 population along with 95% confidence intervals, overall and stratified for sex and age (strata: 0-59 years of age, with a 10- year strata, years of age, with a 5-year strata, last stratum 90), and region (Eastern and Western Germany, Berlin excluded, since no East West-specific data available), assuming Poisson distribution. To account for recurrent admissions and double registrations, we used the carefully evaluated correction factor of 0.89 to estimate first admissions,which means patients with at least one hospital admission due to hip fracture per year [16]. We standardized rates to the German population in To analyze the hip fracture incidence trends between 1995 and 2004 in the whole population and in the various strata, we used multiple Poisson regression including age and/or sex as confounders. We estimated age/ sex adjusted average annual changes (incidence rate ratios, IRR) and changes over the whole study period of 10 years as average 9-year change IRR 9, corresponding to the multiplicative model. Two-sided 95% confidence intervals of IRRs were computed based on the profile likelihood function. Interaction terms were included to evaluate differences in the trend of hip fractures between men and women and Western and Eastern Germany. To take into account overdispersion, we performed all analyses with dscale adjustment [17]. All analyses were performed using the Statistical Analysis Systems SAS (SAS for XP PRO, Release 9.1 TS1M3, SAS Institute Inc. Cary, NC, USA). Results Population The German population increased from 81.8 million in 1995 to 82.5 million in The proportion of younger subjects decreased (people aged 0-39 years: 52.3% in 1995, 46.8% in 2004), whereas the proportion of higher age groups increased (proportion of people aged 65 or older: 15.6% in 1995, 18.6% in 2004), particularly the oldest old (subjects aged 80 years or older: 4.0% in 1995, 4.3% in 2004). More detailed data are available from the authors.

3 Numbers and crude incidences of hip fractures The number of hospital discharges for hip fractures in Germany increased, from 111,394 in 1995, to 130,653 in After correction for double registration and readmissions, there were 99,141 and 116,281 patients with at least one hospital admission in 1995 and 2004, respectively, corresponding to crude incidences of (95% confidence interval ) per 100,000 population in 1995 and ( ) per 100,000 in Trend of hip fracture incidence Table 1 shows standardized incidences between 1995 and 2004 for the whole population, as well as stratified by sex, and by region. Age- and sex-specific incidence rates are presented as well as the average annual changes and changes over the whole study period Figure 1 displays age- and sex-specific incidence rates in Eastern and Western Germany. As expected, incidence rates were higher in older age groups over the whole study period. In younger people, incidences were higher in men, and they were much higher in elderly women. Except in young men, incidences were higher in Western compared to Eastern Germany. Overall, there was a statistically significant, but only slight increase of the hip fracture incidence of about 1% per year (average annual change: IRR 1.01; 95% confidence interval , p<0.01). The total increase between 1995 and 2004 was 5% (IRR 1.05; , p<0.01). However, the trends differed markedly by age, sex, and region (Table 1). In men aged 40 years or older, incidences increased in most age groups, in particular in subjects aged 85 to 89 years. In women aged 40 years or older, there was a tendency of a decrease up to the age of 74 years, but a pronounced increase in subjects aged 75 to 79 and subjects older than 85 years. However, interaction between trend and sex was not significant (p=0.89). In younger age groups, there was a marked decline in the hip fracture incidence (IRR , age group 0-39 years: men 0.74; , women 0.62; , both p<0.01). The increase between 1995 and 2004 was significantly higher in Eastern compared to Western Germany (interaction term: p=0.002). This trend could be seen especially in older age groups. Thus, the difference between East and West Germany decreased. Discussion Main findings From an international point of view, only few studies have evaluated actual trends of hip fracture incidence. This is the first analysis presenting trends of hip fractures for whole Germany. Without age- and sex-adjustment, we found a relevant increase in the total number and incidence of hip fractures, paralleling the aging of the population. After adjustment for age and sex, we found a statistically significant but, only slight increase of the hip fracture incidence. In comparison to an earlier study on incidence data from Eastern Germany up to 1995 observing a high average annual increase from 3% to 6% [4], our analysis suggests a leveling off since the middle of the 1990s. Trends differed between men and women, with a lower increase or even a decrease in women. An incidence increase seemed to be particularly present in older subjects, in contrast to younger age groups, where the incidence declined. As in 1995, the incidence was still higher in Western Germany, however, with a reduction of the difference between Eastern and Western Germany over time. Comparison to other studies We found the hip fracture incidence in Germany to be lower than in Scandinavian countries [8, 18], and higher compared to Spain and Serbia [10, 19]. This result is in accordance with a former analysis by Johnell et al. [20]. Some of the studies which have evaluated hip fracture trends, in particular those that evaluated earlier data and those from Northern and Eastern Europe, found an increase [3 7, 19], whereas other, more recent studies found a leveling off similar to our study or even a decrease during the past decade [8 11, 14]. Most studies were limited to subjects of 50 years or older. In this age group, we found an annual increase of 0.6%, resulting in a 6% increase over the period 1995 to Few studies found different patterns for men and women. Löfmann et al. found an incidence increase in men, and a decrease in women [13]. Chevalley et al. reported a reduction in women between 1991 and 2000, but no incidence change in men [15]. The observation of a more pronounced hip fracture incidence in elderly men is in line with our findings. To the best of our knowledge, no study investigated incidence trends in younger age groups. The observed decrease in people younger than 40 years in our study is striking [21]. Already in the middle of the 1990s, the incidence of hip fractures was found to be higher in Western Germany [4]. The higher increase in the Eastern compared to the Western part of Germany, resulting in a decrease of the difference between Eastern and Western Germany, is of particular interest. Implications of the study findings It has been suggested that hip fractures in different age groups represent different etiologies and hence should be

4 Table 1 Incidence rates of hip fractures and trends in Germany, 1995 to IRR per year IRR Total a ** 1.05 ( ) Men b ** 1.07 ( ) Women b ** 1.05 ( )) East-G c ** 1.13 ( ) West-G c * 1.03 ( ) Male, age ** 0.51 ( ) ** 0.69 ( ) ** 0.65 ( ) ** 0.84 ( ) ( ) ( ) ** 1.18 ( ) ( ) ** 1.10 ( ) ** 1.16 ( ) ( ) ** 1.37 ( ) ** 1.13 ( ) Female, age ** 0.41 ( ) ** 0.53 ( ) ** 0.57 ( ) ** 0.76 ( ) ( ) ( ) * 0.92 ( ) ** 0.78 ( ) ** 0.90 ( ) ** 1.20 ( ) ( ) ** 1.23 ( ) * 1.06 ( ) a Standardized to the German population in b Age-standardized c Age-sex-standardized, without Berlin (no East West-specific data available) Incidence rates per 100,000 (95% confidence interval). IRR: Incidence rate ratio (95% confidence interval) from age-sex-adjusted Poisson regression * p<0.05 ** p<0.01 regarded separately. In younger age groups, hip fractures are mainly induced by major traumatic causes like car and working accidents or sports injuries. The decrease in younger people is probably due to a reduction in severe injuries in association with working and traffic accidents [21], as has been shown in several countries [22, 23]. Hip fractures in the elderly are mainly due to osteoporosis and falls with relatively minor external trauma. A leveling off of the earlier observed secular trend may be due to a combination of period and cohort effects. In earlier birth cohorts, the early-life risk factors for fracture may have had stronger impact on the late-life fracture risk than in the others [12]. It is also conceivable that the increase of average body weight and body mass index may reduce the risk of fracture [24]. The tendency of a lower increase or even a decrease among elderly women compared to rates in male subjects could arise from more specific prevention and treatment of osteoporosis. However, there is a lack of sufficient evidence on a secular change in Germany [24, 25]. The earlier menarche and the extension of the age of menopause, combined with a lower fertility may contribute to a relative reduction of the risk of osteoporotic fractures in women. Finally, falls and fracture prevention programs in the elderly introduced in Germany during the past decade may have contributed to a relative lowering of the risk of hip fractures, in particular in people up to 85 years of age [26, 27]. The regional difference between Eastern and Western Germany with a higher increase in the East is of special interest. The reasons are unknown so far. Different ways of life (nutrition, activity level) and environmental conditions may have been responsible for the lower risk of hip

5 Hip fracture incidence, Western Germany, Men 1200,0 1000,0 800,0 Incidence per 100, ,0 400,0 0 to to to to ,0 0, Year Hip fracture incidence, Eastern Germany, Men 1200,0 1000,0 800,0 Incidence per 100, ,0 400,0 0 to to to to ,0 0, Year Without Berlin Fig. 1 Age-sex specific incidences in Eastern and Western Germany

6 fractures in Eastern Germany, and a convergent change of life patterns and conditions, since the re-unification may contribute to a leveling off between the two parts of Germany [4]. Limitations Several limitations have to be considered [1]. Misclassification within the hospital discharge register due to coding mistakes has to be assumed. The classification system changed in 1999 (ICD 9 to ICD 10). However, hip fractures are clearly categorized in both versions of the ICD, and hip fracture coding has been proven for accuracy [4]. The register does not allow evaluation of reasons of hip fractures. Nevertheless, the hospital discharge register has been shown to be a valid instrument [2, 4]. We used a correction factor to account for double registrations and recurrent admissions, which has been carefully evaluated in Germany [16]. Nevertheless, it cannot be excluded that the number of recurrent hospital admissions changed over the study period [4]. Furthermore, readmissions may differ with age and sex. However, a constant correction factor has been regularly used in incidence trend studies [4, 20]. Nevertheless, future studies should examine the correction factor with respect to its variability with time, sociodemographic variables, and region [3]. Cohort effects for hip fracture incidence have been shown [28]. We did not apply age period cohort models, since there is an ongoing controversial debate on the most appropriate model to adjust for age, period, and cohort. In conclusion, after adjusting for age and sex, we found only a slight increase in the incidence of hip fractures compared to higher rises in the past which have been found in the Eastern part of Germany. Thus, assuming a continuation of the trend of the past decade, a further increase should not exceed much of what is expected from the demographic aging of the population. The differences in the trends in Eastern and Western Germany should be evaluated in further studies. The identification of causes may provide valuable insights into the origin of secular trends and may provide important clues for prevention. The reported heterogeneity of trends between sex, age groups, and regions is a major finding of our study. Future analysis of hip fractures trends should include stratification for these socio-demographic determinants for a better understanding of the differences in hip fracture incidence trends between socio-demographically defined subpopulations within and across countries. The decline in younger age groups may reflect developments following prevention of working and traffic accidents, which are worth monitoring in their own right. Acknowledgement The study was supported by a grant from the North-Rhine Westphalian Ministry of Health and Social Services. We would like the Health Counselling Committee of the North-Rhine Westphalian Chamber of Physicians (Head Dr. Arnold Schüller) for their support. We would further like to thank Dr. Olaf Schoffer, Research Department of the National Statistical Office, for his support in data management, and Prof. Florian Gebhard, Clinic of Surgery, University of Ulm, for his support in interpreting the results. Funding The study was supported by a grant from the North-Rhine Westphalian Ministry of Health and Social Services. Conflict of interest statement conflict of interest. References All authors declare that they have no 1. Cummings SR, Melton LJ (2002) Epidemiology and outcomes of osteoporotic fractures. Lancet 359: Keene GS, Parker MJ, Pryor GA (1993) Mortality and morbidity after hip fractures. BMJ 307: Kannus P, Pakkari J, Niemi S (1995) Age-adjusted incidence of hip fractures. Lancet 346: Wildner M, Clark DE (2001) Hip fracture incidence in East and West Germany. 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