Mortality following hip fracture has been the focus of many investigations carried out over the past 25 years (1
). Although it is well-recognized that mortality is elevated following hip fracture, controversy remains regarding the extent to which mortality may be reduced through hip fracture prevention because those at highest risk of hip fracture are frail and elderly and already at increased mortality risk. Our analysis of an MCBS survey cohort, a representative sample of the U.S. Medicare population, indicates that hip fracture is associated with excess early mortality, but we found no evidence of excess mortality risk beyond the first six months following fracture. This is important, because estimates of the impact of hip fracture prevention on population health may be exaggerated if excess long-term mortality is assumed when this is not appropriate.
Our finding of high excess mortality close to the time of fracture is consistent with other reports (7
). Regardless of study design, investigations that have examined mortality by time since hip fracture have noted the highest excess risk closest to the time of fracture. The duration of the early elevated excess risk is most commonly reported as six months, but ranges from 3 months to 12 months.
In contrast to several studies that report significant long-term excess mortality (8
), we found no evidence of excess mortality beyond six months following fracture. A prominent difference between those reports and ours is the nature of the study population. Our study population is representative of the elderly U.S. population and includes those who are institutionalized. Thus, our study cohort differs in health from the community-dwelling ambulatory elderly cohorts that have been the focus of other reports (12
). The extent to which a healthy cohort may influence estimates of long-term excess mortality is exemplified by Magaziner et al.
) who highlighted the potential for long-term excess mortality in those with few ADL/IADL impairments or with few comorbid conditions. This may help explain divergent findings from our nationally representative cohort of elders, for which no long-term excess was observed, and findings from healthier longitudinal cohorts such as EPIDOS (12
), for which continued excess risk was noted.
Differing methodological approaches to characterizing excess mortality in other studies may also have resulted in higher long-term risks than those we report. In particular, studies that rely on comparisons between mortality in hip fracture patients relative to age- and sex-specific expected mortality in the general population (13
) may not have adequately accounted for the pre-fracture frailty and illness in those who sustain a hip fracture relative to their peers. As a result, these studies may suggest a much greater adverse health impact associated with fracture than is warranted. Likewise, case-control studies matched on age and a retrospective review of health conditions are unlikely to adequately control for pre-fracture health (15
Our ability to adjust for detailed pre-fracture functional status using prospectively collected longitudinal data in a nationally representative sample is a key strength of our study. As with any longitudinal study, however, our findings are predicated on the quality of follow-up over the period studied. An in-depth evaluation of the impact of non-response on MCBS survey estimates over the period 1997 to 1999 showed favorable initial participation and follow-up rates (83% participation, with panel attrition of 11%, 5%, and 3% in the initial, second and third survey years). Both initial non-response and attrition were lower among those in poor versus better health. Current MCBS non-response procedures have been found to substantially reduce or eliminate potential non-response bias (21
Our analysis of mortality following hip fracture did not account for clinical presentation, the timing or type of fracture repair, which have been the focus of other studies (35
). Still, the difference in mortality attributable to hip fracture when considering only age, sex, and race in comparison to more fully adjusted estimates highlights the importance of pre-fracture health and functional status as an important predictor of death. We note that whether or not socioeconomic factors were included in the analyses had no impact on mortality following hip fracture (Model 2 and Model 3 comparison). Although attributable mortality increases with age, it is reduced by approximately 50% when pre-fracture health, functional status and factors other than age, sex and race alone are considered. For example, to estimate the number of potentially preventable deaths in the elderly U.S. population, we applied our estimates of attributable risk to the total number of deaths observed in the Medicare population (ages 65 and older who were not covered by managed care) in the year 2000. When only adjusting for age, sex and race, 79,370 of 971,570 deaths among women and 27,890 of 764,350 deaths among men were attributable to hip fracture. When adjusting for pre-fracture health status, the number of deaths attributable to hip fracture dropped to 40,690 in women and 13,930 in men. Thus, although short-term mortality may be prevented through hip fracture prevention, the extent to which longevity in the community may be improved by treatment remains uncertain (10
Our analyses of the impact of hip fracture on short- and long-term excess mortality for specific population subgroups may provide some additional insights. Although we found evidence of higher mortality in men than in women (see for main effects of sex), a finding consistent with other reports (15
), mortality between men and women did not appear to differ according to whether or not a hip fracture occurred. This finding contrasts with a report from the 15-year longitudinal Cardiovascular Health Study that found only 6-month excess mortality in men, but 4-year excess mortality in women (43
) Although our stratified analysis indicated potentially worse hip fracture mortality for non-blacks compared to blacks and for non-facility dwellers compared to facility-dwellers, these did not appear to differ according to whether or not a hip fracture occurred. Larger studies based on Medicare Claims data (42
), have reported significant sex and race interactions, with black females having the poorest outcomes, but we did not have sufficient power to examine sex-race interactions in our population. In addition, we did not have sufficient power to examine such interactions in the context of early and late excess hip fracture mortality risks.
Although our analysis focuses on excess mortality following hip fracture, excess mortality following other fractures is also of concern (33
). Separating out the effects of comorbid conditions from fracture complications is challenging. Unfortunately, the difficulty in accurately identifying vertebral fractures in claims data precludes a similar analytic approach to estimating excess vertebral mortality risk using the MCBS survey cohort.
In summary, although it may be possible to prevent a subset of early deaths, preventable excess long-term mortality is likely to be quite modest and therefore difficult to identify in any study using conventional statistical approaches unless an extremely large population is studied (10
). Our study indicates that fracture prevention may be of limited benefit in extending overall life expectancy due to the multiple competing mortality risks faced by the frail elderly.