1 Department of Epidemiology and Preventive Medicine, School of Medicine, University of Maryland, Baltimore, MD.
2 Department of Epidemiology and Biostatistics, School of Public Health, Boston University, Boston, MA.
3 School of Social Work, University of North Carolina, Chapel Hill, NC.
Received for publication September 12, 2001; accepted for publication November 11, 2002.
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ABSTRACT |
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activities of daily living; aging; disability evaluation; disabled persons; hip fractures
Abbreviations: Abbreviations: ADL, activities of daily living; BHS, Baltimore Hip Studies; EPESE, Established Populations for Epidemiologic Studies of the Elderly.
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INTRODUCTION |
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Despite changes in functioning after hip fracture, the extent to which these changes can be attributed to the fracture remains uncertain; identifying this excess loss is important for understanding the level of recovery that can be expected following a fracture. Several studies (2022, 24, 25) have reported increased impairment in physical and instrumental functioning relative to prefracture status for as long as 2 years after fracture. However, these studies lacked comparison groups and could not evaluate how much of the functional decline was due to the hip fracture and how much would have occurred in this vulnerable population even without fracture.
Three cohort studies of community-dwelling aged evaluated changes in functional status among respondents who fractured a hip compared with those who had not (2628). These studies found that, over follow-up periods of 6 months to 6 years, hip fracture patients had greater losses regarding activities of daily living (ADL) than same-aged persons who had not fractured a hip. Although these studies provide more evidence for functional impairment resulting from hip fracture than studies without comparison groups, they lack information on functional status immediately prior to the fracture and therefore cannot be used to determine how much of the observed decline preceded the fracture and how much followed it. Ideally, functional status should be measured just prior to the fracture and at multiple time points afterwards as well as at similar intervals for a comparison group. Functional status around the time of hip fracture can be assessed more accurately by identifying hip fracture patients when they are hospitalized (20, 2325, 29, 30). However, it is difficult to identify an appropriate nonfracture comparison group since the demographic and health characteristics of hip fracture patients differ from those of many other groups of older persons.
The objective of this study was to estimate the change in physical function attributable to hip fracture. A cohort of hip fracture patients was followed prospectively from the point of fracture and was compared with a group of community-dwelling aged from the Established Populations for Epidemiologic Studies of the Elderly (EPESE) (31) matched by age, sex, and functional status. Changes in disability, defined as the inability to perform three ADL either independently or with assistance (human or equipment), were evaluated. Two ADL, walking across a room and transferring from bed to chair, require lower-extremity mobility and are likely affected by hip fracture; the third activity of daily living, grooming oneself, is an upper body task that should not be substantially affected by hip fracture. In addition, because baseline functional limitations are strongly associated with subsequent functional decline (32) as well as excess mortality following hip fracture (33), changes in these ADL after hip fracture were compared by level of preexisting comorbidity, functional limitations, and age.
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MATERIALS AND METHODS |
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Hip fracture patients
These subjects participated in a study of health outcomes among patients aged 65 years or older who were admitted consecutively to one of eight hospitals in the Baltimore, Maryland, area during 19901991. Patients were excluded if they presented with pathologic fractures or resided in a nursing home, hospital, or extended-care facility. Of the 804 patients, 674 enrolled in a 2-year follow-up protocol. Additional information about construction of the sample can be found elsewhere (25). Data were collected through chart review and questionnaires administered in face-to-face interviews with patients (or a proxy if necessary) during the initial hospitalization. Face-to-face follow-up interviews were conducted with patients or proxies at 2, 6, 12, 18, and 24 months after hospitalization for hip fracture.
Comparison group
This group was derived from EPESE, a prospective study of risk factors associated with chronic disease, loss of functioning, and mortality among community-dwelling adults aged 65 years or older conducted at four sites in the United States: Massachusetts, Iowa, Connecticut, and North Carolina. Prospective data were available from three sites; therefore, our cohort was drawn from samples in Massachusetts (n = 3,421), Iowa (n = 3,492), and Connecticut (n = 2,539). A more complete description of the EPESE study can be found elsewhere (31, 32). Data were collected annually from 1982 through 1984. Face-to-face interviews were conducted with respondents or proxies (when necessary) at baseline, and telephone interviews were conducted during 12-month and 24-month follow-up. Previous evaluations of concordance between telephone and face-to-face reports of function have reported no notable differences in responses (34, 35).
Measures
Functional status was measured by self-reported ability to perform ADL. Three ADL questions were selected because they were worded similarly in the two studies: 1) walking indoors (BHS: "walk 10 feet (3 m) or across a room"; EPESE: "walking across a room"), 2) transferring from bed to chair (BHS: "get in and out of bed"; EPESE: "get from a bed to a chair"), and 3) grooming (BHS: "groom yourself (that is, brush hair and teeth); EPESE: "personal grooming such as brushing hair and teeth, or washing face"). In previous studies (27, 36), walking indoors and transferring have been associated with decline in lower-extremity functioning.
The ADL questions and response options differed slightly between the studies. In BHS, respondents were asked whether they had received help performing each activity of daily living during the past week. Baseline functioning referred to the week before the hip fracture. Response options were as follows: received no help, used help from equipment or a person, or unable to perform activity. In EPESE, respondents were asked whether there had been any time in the past 12 months when they needed help from a person or equipment to perform the activity. Response options were as follows: does not need help, gets help, or is unable to perform activity. To resolve differences, responses were recoded to "unable to perform or performs activity with assistance" versus other. In this paper, the percentage of those "unable to perform" at a specific time point is henceforth referred to as the disability rate.
Covariables available for both groups included age, sex, and five comorbid health conditions (diabetes, hypertension, cancer, stroke, and heart disease).
Merging the cohorts
The BHS cohort was older than the EPESE group and evidenced more limitations regarding ADL tasks. To minimize baseline differences between these groups, each of the three EPESE cohorts was frequency matched to the BHS cohort on sex, 5-year age group, and ability to walk indoors at baseline. Ability to walk indoors was selected for matching because of its prime importance in recovery from hip fracture and its strong association with other lower-extremity tasks of daily living. The matching procedure is described in detail elsewhere (37).
Analyses
For each activity of daily living, the proportion of respondents in the hip fracture sample disabled at baseline, 12 months, and 24 months was compared with the corresponding proportion for each of the three matched EPESE samples. Because the data are longitudinal, these comparisons were not statistically independent. Thus, appropriate standard errors were derived by fitting generalized estimating equation models (38) to account for intrasubject correlation across the follow-up period. The dependent variable was disability (yes or no); the independent variables included indicator variables for group (BHS or EPESE), time (baseline, 12 months, 24 months), and group-by-time interactions. A log-link function, an unstructured covariance matrix, and a binomial error distribution were specified for the generalized estimating equation models. Model predictions were transformed to probabilities of disability through exponentiation.
To evaluate whether baseline comorbidities and functional status modified associations between having a hip fracture and ADL outcomes, three additional stratified analyses were conducted: one stratified by whether the respondent had one or more of three diseases at baseline (heart disease, cancer, or stroke) or was free of these diseases, a second stratified by whether the respondent was able or unable to walk across the room at baseline, and a third stratified by age (less than age 85 years vs. 85 years or older).
Attributable disability rates were computed as the change in disability rate from baseline to 24 months for the BHS cohort minus the change in disability rate from baseline to 24 months for the EPESE cohort. EPESE values were determined from the average of the disability rates over the three sites.
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RESULTS |
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DISCUSSION |
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Our results are consistent with those from three previous studies that compared change in functional status among hip fracture patients versus other elderly adults (2628). A study of the New Haven, Connecticut, EPESE cohort found that 120 respondents who had fractured a hip had significantly more of a decline in their ability to dress, transfer from bed to chair, walk across a room, climb stairs, and walk half a mile (0.8 km) over 6-week and 6-month follow-up periods than did 206 respondents, matched on age, sex, and functional ability, who had not fractured a hip (26). These results were observed regardless of baseline physical functioning of hip fracture patients. We also found a greater functional decline in hip fracture patients than in other respondents whether or not comorbidity or walking disability was reported at baseline. However, a smaller proportion of our hip fracture patients had disabilities in transferring (38 percent vs. 68 percent) and walking across a room (54 percent vs. 85 percent) at 12 months, which might have been due to differences in the follow-up periods.
Likewise, 108 Longitudinal Study on Aging participants who fractured a hip over a 6-year period had significantly more disability in five categories of functioning after fracture than 4,030 study participants who had not fractured a hip (27). As in our study, respondents who fractured a hip during follow-up declined more in basic ADL (bathing, dressing, transferring in and out of bed, toileting, getting outside, and walking) and upper-body functioning (difficulty sitting, reaching up overhead, reaching out as if to shake hands, and using the fingers to grasp objects). Similarly, elderly Stockholm, Sweden, residents who had been hospitalized for a hip fracture and were functionally independent were more likely to become disabled regarding at least one of six ADL (bathing, dressing, toileting, transferring, continence, and feeding) over a 3-year period than functionally independent respondents who had not fractured a hip (28). Furthermore, among respondents who had ADL limitations at baseline, hip fracture increased the risk of functional decline over the follow-up period.
Together, these studies provide evidence that elderly persons who fracture a hip decline in both lower-extremity functioning and upper-extremity functioning over follow-up periods ranging from 6 weeks to 6 years. In the present study, most of the decline in walking and transferring ability occurred during the first 12 months. As expected, the impact of fracture on grooming was much smaller than on lower-extremity tasks. While the observed small excess loss may have been due to measurement differences between the cohorts or bias not accounted for by the analytic approach, it may also be a convalescent phenomenon associated with depressed mood, reduced ability to be mobile, and general reduction in activity (25).
The characteristics of our sample were similar to those in the study samples cited above (2628), even though our hip fracture patients were identified when they were hospitalized for fracture and our comparison subjects were community-dwelling elderly persons matched to hip fracture patients on sex, age, and functional status. In our sample, the prevalence of baseline disability in transferring and walking was similar to that in the Marottoli et al. study (26). The hip fracture patients also had similar mortality rates: 16 percent of our sample died over a 1-year period; about 20 percent died within the first year postfracture in the other studies (26, 27). The three EPESE cohorts in the present study were analyzed separately rather than merged into a single comparison group because they represented different groups in the population. The consistent results observed provide a reliable base for comparison and underscore the fact that hip fracture patients experience more functional decline over a 2-year period than sex-, age-, and function-matched peers.
The current study has several methodological strengths compared with previous studies. First, inclusion of a comparison group of elderly persons who had not fractured a hip enabled us to evaluate functional decline due to hip fracture versus that due to aging. Second, the design permitted measurement of functional status closer to the time of the fracture than in previous studies using comparison groups (2628). Third, the repeated-measure analysis provided estimates of changes in functional status over the 2-year study period that accounted for correlations in persons functional status over time. Previous studies assessed functional status only once postfracture (2628). Fourth, subjects in the EPESE and BHS cohorts were followed at the same intervals and for the same amount of time. By contrast, previous analyses of EPESE participants used a 1-year follow-up period for controls and a 6-month follow-up for hip fracture patients (26), and the analyses of the Longitudinal Study on Aging were restricted to a subset of respondents who participated in the 1990 follow-up interview (27). This study had a larger sample of hip fracture patients than previous ones (2628). Furthermore, in contrast to previous studies, the groups in the present study were frequency matched on selected confounders, which increased the statistical power to detect and isolate an effect of hip fracture on functional decline.
This study had limitations as well. Differential loss to follow-up and use of proxies may have introduced bias in attributable disability estimates. There were more deaths in the hip fracture (16.1 percent) than in the EPESE (8.7 percent) cohorts over a year. Although use of generalized estimating equations enables subjects outcomes to contribute to the results while they are alive, those who died probably would have had the worst outcomes, thus producing an underestimate or a conservative view of the true attributable disability. Losses for other reasons were smaller in the hip fracture (1 percent) than in the EPESE (12.1 percent) cohorts. To the extent that those lost were more disabled than those retained, it is possible that the observed attributable disability overestimated the actual attributable disability. The differential use of proxies to obtain information from hip fracture patients and EPESE controls introduced another potential source of bias. Similar proportions of participants in the BHS (15.7 percent) and EPESE (15.2 percent) cohorts had proxy responses during follow-up; however, at baseline, 28 percent of the BHS information came from proxies compared with 17.2 percent in EPESE. Because proxies tend to overreport disability (39, 40), the baseline difference may produce more false positives in BHS than EPESE, thereby reducing the number of hip fracture patients for whom new disability can be reported and resulting in an underestimate or conservative estimate of the actual attributable disability. Whether underestimates stemming from differential survival or use of proxies compensate for possible overestimates attributable to losses for other reasons cannot be ascertained accurately; however, overall, the net bias stemming from differential survival or use of proxies is likely to be small.
Different reference frames regarding measures and period of cohort acquisition also may have affected attributable disability estimates. Because estimates of baseline ADL functioning used different intervals (1 week in BHS vs. 12 months in EPESE), the prevalence of disability in EPESE could reflect episodes that occurred and resolved during the year preceding the interview, thereby attenuating the disability estimate. In addition, BHS and EPESE data were collected approximately 8 years apart. Although we are aware of no notable changes in the management of hip fracture or disability during this period, findings suggesting that more recent cohorts of older persons are less disabled (41) raise the possibility that changes in BHS patients are smaller than those in EPESE participants. Although we do not think that the effect would be great since we adjusted for comorbidity and functional differences between the groups, any effect would also favor an underestimate of disability attributable to hip fracture.
Because of the limited number of measures obtained in a similar manner in BHS and EPESE, we assessed change in only three ADL and controlled for a limited number of confounding variables. Nonetheless, these ADL have been studied extensively as important outcomes (2127). Finally, although results of this study are generalizable mainly to older White women, they provide important information for health care providers because this group has the highest risk of hip fracture (1).
We used a novel method to construct a comparison group of community-dwelling older adults to evaluate whether hip fracture patients experienced more functional disability than would be expected in a similar group who did not fracture. Although we could not evaluate whether those who fracture decline at a different rate before fracture and would consequently have a different level of function a year or two later than the nonfracture comparison group, results do indicate that hip fracture patients have higher levels of disability than expected over a 2-year follow-up period regarding three ADL that reflect both lower-extremity and upper-extremity functioning. The excess disability in these functions attributable to hip fracture was substantial and was not restricted to special subgroups (table 3). Comparing hip fracture patients with matched groups in the general population identifies a level of improvement to strive for when intervening to maximize functional recovery after hip fracture. These results provide an estimate of the amount of disability attributable to hip fracture. Results add to the evidence that hip fracture produces a substantial decline in functioning, and they support the need for interventions to prevent fracture and to improve rehabilitation and treatment for older persons who fracture a hip.
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ACKNOWLEDGMENTS |
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The authors acknowledge the participation of the following hospitals in the Baltimore Hip Studies: Baltimore County General Hospital (currently Northwest Medical Center), Franklin Square Hospital, Greater Baltimore Medical Center, Saint Agnes Hospital, Saint Joseph Hospital, Sinai Hospital of Baltimore, Union Memorial Hospital, and the University of Maryland Medical System. They also acknowledge the thoughtful comments on an earlier draft of this paper from Dr. Anne Cappola, assistance with analyses and graphics from Justine Golden, and careful manuscript preparation from Yvonne Aro.
A portion of this paper was presented as part of the symposium entitled "Public Use Datasets to Study Health Outcomes: Hip Fracture as an Example" at the 51st Annual Scientific Meeting of The Gerontological Society of America, Philadelphia, Pennsylvania, November 1998.
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NOTES |
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REFERENCES |
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