Incidence and Mortality Following Hip Fracture in Korea

Of all fracture types in the elderly resulting from osteoporosis, hip fracture is the most serious, and has high associated levels of morbidity and mortality. In many countries, populations are aging and many studies have reported significant increases in the incidence of hip fracture with age (1, 2). It has been estimated that in 2050, approximately 50% of all hip fractures in the world will occur in Asia (2, 3), and thus, it is expected that hip fractures are likely to present a serious socioeconomic problem in developing Asian countries (2, 4, 5). Recently, population-based epidemiologic studies on hip fracture in Asia have reported relatively high incidences of hip fracture, and confirmed that the number of hip fractures is likely to increase markedly in the near future (4-6).

In contrast with studies on the incidence of hip fracture, morbidity and mortality studies related to hip fracture in Asia are rare, and the studies have been performed with limited sample size (7-9). Even though many epidemiologic studies related to mortality and morbidity following hip fracture have been published in the western countries (10), these studies cannot be used for reference purposes due to geographical variations (11, 12).

In this study, we evaluated nationwide data regarding incidence and mortality after hip fracture in Korea by using administrative claims database of the Health Insurance Review and Assessment Service (HIRA), which comprises of fully adjudicated medical and pharmacy claims for 50 million beneficiaries in Korea. Every clinic, hospital and pharmacy in Korea is obliged to submit patient data regarding healthcare services and medical costs to the HIRA for reimbursement. The purpose of this study is to assess incidences of hip fracture, patterns of mortality following hip fracture in the entire population, and to document excess mortality due to hip fracture in people over 50 yr of age in Korea.

The present study is the first nationwide, database-based, observational study of hip fracture conducted in Korea in terms of its incidence, mortality, and excess mortality. After the complete computerization of the claims database in 2005, HIRA data now represent a secure source of data that can be easily studied. From 2005 to 2008, the number of hip fractures increased by 21% (from 16,866 in 2005 to 20,432 in 2008) and the annual hip fracture incidence increased by 2.3% (from 147.6/100,000 to 156.6/100,000). Our data show that the age-standardized annual incidence of hip fractures was 199.4/100,000 for women and 94.5/100,000 for men in 2008. In agreement with previous studies on the incidence of hip fracture in Korea, the incidence of hip fracture has increased. Kang et al. (9) performed a cohort study using HIRA data and reported age-standardized annual incidence rates for hip fractures: 146.38/100,000 for women and 61.72/100,000 for men in 2003. Recently, Kim et al. (14) performed a cohort study using hospital based record and radiographic data and analyzed hip fracture incidence in Jeju island over a five-year period (2002-2006). They reported that the crude incidence rate of hip fractures was 174.4/100,000 for women and 66.1/100,000 for men (14). However, a higher incidence of hip fracture using HIRA data has been reported by Lim et al. (13). They reported that the age-standardized annual incidence rates of hip fracture were 262.8/100,000 for women and 151.8/100,000 for men in 2003 (13). A comparison of the three findings indicates that results of Lim et al. (13) were somewhat overestimated. In our consideration, this discrepancy emerged due to the difference in operational definition of the hip fracture using HIRA data (9, 13, 14). Lim et al.'s study was not used in the operational definition of the hip fracture but they used only on ICD code (S72.0 and S72.1). We have confirmed that the incidence of hip fracture, using only ICD codes (S72.0 and S72.1) was four times higher than the incidence of hip fracture with using the operational definition.

Rates of hip fracture in Korea that can be found in the present study are slightly higher than the rates reported by population-based studies conducted in South East Asia (Thailand and Malaysia) (4), China (18, 19), and Mexico (20), but lower than the rates reported in other Asian countries such as Japan (5), Hong Kong (4), and Singapore (4), and those in Norway (21), and the United States (22). Recently, some studies report that incidence of hip fracture in some countries such as Japan, Austria, and France shows steady or decreasing trend (23-25). However, hip fractures in Korea are projected to increase dramatically because the rate of the increase of the elderly population in Korea is greater than that of anywhere else in the world.

In this study, the cumulative mortality rate after hip fracture continued to increase throughout the study period, and the crude mortality rate in patients over 50 yr of age at 1-yr post-injury was 17.8% (21.8% in men and 16.2% in women). Although the crude mortality rate in Korean population is similar to that reported by others (7, 8, 26, 27), the crude mortality at one-year post-fracture varies due to population heterogeneity with respect to age, pre-fracture health status, socio-economic status, and mental health. Recently, Abrahamsen et al. (10) performed a meta-analysis of mortality after hip fracture and reviewed 1,114 studies. They reported that the crude mortality rate at one-year post-fracture ranged from 50% to 5.9% (8, 27-29).

To compare mortality after hip fracture with that in other studies, we calculated SMRs. Although direct comparisons were difficult, it was possible to compare mortalities. In our study, the SMRs of patients who were older than 50 yr were averaged at 6.1 at 3 months, 3.5 at 1 yr, and 2.3 at 2 yr post-fracture. Tsuboi et al. (8) performed a 10-yr follow-up study on hip fracture mortality in 1,169 patients who were older than 50 yr. They reported that SMRs were 2.7 at 1 yr, 2.0 at 2 yr, 1.7 at 5 yr, and 1.94 at 10 yr. Richmond et al. (26) performed an observational study on 836 hip fracture patients older than 65 yr, and reported that SMR peaked at 2.8 at 3 months post-fracture. However, excess mortality was still observed at 2 yr post-fracture with an overall SMR of 1.3 (26). Although there was a difference between their report and ours due to the nature of the study population, the trends of the two studies are similar. The reason for the higher SMR observed in this study is related to patient age, which is inversely correlated with SMR. In addition, we found that SMR is inversely correlated with cumulative crude mortality rates and that it decreases over the course of follow-up. Therefore, the present study shows that excess risk of mortality is the greatest during the immediate post-fracture period.

In this study, male mortality after hip fracture was found to be 1.4 times higher than female mortality. Other studies have reported that male mortality is about twice as high as female mortality during the first year post-fracture (9, 30). Although reports tend to differ regarding male mortality rates, this finding is consistent with other studies. In these studies, it was demonstrated that the reasons for higher male mortality are: comorbidities, higher infection rates, poor osteoporosis management, and a higher risk of postoperative complications (9, 30).

This study has some limitations. First, incidences based on insurance claims records might be underestimated. For example, hip fractures may not be diagnosed or treated by health care institutions. However, due to the emergent character of hip fracture, it requires hospitalization, and thus we believe that the incidence of hip fractures determined using claims records represents reality. In addition, contralateral hip fracture which could occur within 6 months and nonoperatively treated hip fracture such as impacted femoral neck fractures were not included. This was the other factor of underestimation.

Second, the reliance on ICD-10 diagnostic codes to identify incident fractures may have caused incident hip fractures to be misclassified. In addition, high energy injury such as fall from a height and simple greater trochanteric fracture could be included. However, we confirmed the accuracy of the diagnostic algorithm. In this study, the sensitivity of the algorithm was found to be 93.1% using diagnosis codes from HIRA claims records with respect to direct hospital based record and radiographic data.

Third, the mortality rates of hip fracture were compared with the mortality rates of an age matched general population, which included some hip fracture patients and this potentially may have caused an underestimation of excess associated mortality.

In conclusion, we have shown that the incidence of hip fracture in women showed an increasing tendency from 2005 to 2008. Considering its increasing rate in the elderly population, hip fracture is likely to become a huge socioeconomic burden in Korea. Furthermore, hip fracture has a pronounced excess mortality rate. These findings should be used to alert the general population, health institutions, and health policy decision makers to take action on reducing the incidence of hip fracture and minimizing complications after hip fracture.