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Case-control study of hazards in the home and risk of falls and hip fractures.

Introduction

About 30% of people aged 65 years and over fall at least once each year. Hip fractures are the most serious consequence of falls: 16% of women and 5% of men will have a hip fracture during their lives, the majority of these fractures occurring after the age of 75 years [1]. An often-mentioned strategy for preventing falls and fractures is identification of environmental hazards in the home (such as poor lighting, rugs, electrical cords), with subsequent home modifications to make the home a safer place [2-5]. However, the evidence that home hazards increase the risk of falling is meagre-some of the best studies of risk factors for falls have found very little difference in environmental hazards between the homes of fallers and non-fallers [6-8]. To our knowledge, there have been no studies of the relationship between environmental hazards and the risk of hip fractures.

We conducted a case-control study among elderly people referred to the occupational therapy department of a large hospital in the western suburbs of Sydney, Australia. The objective of the study was to determine if the prevalence of various environmental hazards was greater in the homes of people with recurrent falls or a recent hip fracture than in the homes of other elderly people.

Methods

Subjects were selected from people aged 65 years and over seen by an occupational therapist at Sydney's Westmead Hospital for a home assessment. Subjects were recruited over an 18-month period from January 1991 to June 1992.

Subjects were a consecutive series of people referred for a home visit from the geriatric and orthopaedic wards and geriatric domiciliary care service: the most common primary medical problems in these subjects were dementia (n = 64), hip fracture (n= 52), stroke (n = 26), and arthritis (n = 22). (A home visit is done for all patients with a hip fracture admitted to Westmead Hospital who have the potential to return home.)

People were ineligible if they did not live in a private home in the community (n = 120); if they had had a previous home assessment by an occupational therapist (n= 66); or if they had a pathological fracture (n= 3). Otherwise eligible subjects were excluded for the following reasons: transferred to another hospital (n = 5); lived out of area (n = 11); subject died prior to home assessment (n= 1); or subject refused home assessment (n = 1).

One occupational therapist assessed 58% of homes and the remainder were assessed by one of six other occupational therapists. Occupational therapists take into account the functional status of each patient (including general mobility, use of walking aids, and vision) in deciding whether or not features of that patient's home are a hazard. Hence it was not possible to keep occupational therapists unaware of whether they were assessing the home of a case or a control. For people with a recent, sudden change in mobility status (such as hip fracture or stroke), home assessments were completed according to the occupational therapist's judgement of the subject's status prior to this loss of mobility.

The home assessment instrument contained 35 potential hazards and was an abbreviated version of the Westmead Home Safety Assessment, designed for use by occupational therapists in their clinical work. The development and reliability of the instrument is described elsewhere [9]. For those hazards assessed in both the reliability study and the present study, kappas were excellent (kappa ~0.75) for six hazards (floor coverings in internal traffic ways, bed, bed-lighting, bedroom wardrobe, bath-tub, and bath rails); good to fair (kappa: 0.4-0.7;) for 15; and poor (kappa < 0.4) for seven (gates, floor surface in toilet room, toilet, presence of pets, rails on external and internal ramps, and shower rails) [9].

The hazards assessed in this study are listed in 'I'able II. Access-ways were defined as all approaches used bv the resident to get into the house; traffic-ways were defined as the most frequently used route to get from room to room; seating was the chair most frequently used by the subject (including cushions); lighting was assessed as on the day of the home visit; and pets included dogs and cats only. An area of the house was deemed to be hazardous if one or more hazards were identified in it.

Other data collected for this study werenumber of falls in past year; cognitive impairment (based on a rating of nil, mild, moderate or severe according to criteria used routinely by the occupational therapists at Westmead Hospital); number of medications used (from medical records); use of psychotropic medications (from medical records); and type and number of medical conditions (from computerized geriatric department records).

Analyses for recurrent fallers (people with two or more falls in the past year) excluded hip-fracture cases and compared recurrent fallers to non-recurrent fallers (people with one or no falls in the past year). Analyses for hip fractures compared subjects with hip fractures to all other study subjects (combined recurrent and non-recurrent fallers). Data analysis involved crude, stratified and multivariate methods to produce odds ratios and 95% confidence intervals for associations between recurrent falls or hip fractures and home hazards [10]. Multiple logistic regression as used to assess the relationship between recurrent falls and hazards and between hip fractures and hazards, while simultaneously controlling for other variables.

Results

There were 252 eligible subjects: 52 hip fracture cases, 43 people with two or more falls in the past year but no hip fracture (fallers) and 157 subjects with fewer than two falls in the past year and no hip fracture (non-fallers). Ten subjects had missing data on number of falls. Selected characteristics of study subjects are shown in Table I. About 60% of fallers and non-fallers had some degree of cognitive impairment, compared with 39% of hip fracture cases. Use of psychotropic medications was more common among fallers and hip fracture cases than among non-fallers.
Table 1. Characteristics of non-recurrent fallers ([greater than or
equal to]1 fall inpast year), recurrent fallers ([greater than or
equal to]2 falls in past year) and hip fracture cases(a)

                              Non-recurrent  Recurrent  Hip fracture
                              fallers        fallers    cases
                              (n=152)        (n=43)     (n=52)
                              n (%)          n (%)      n (%)
Characteristic
Sex
  Female                      100 (66)       28 (65)    40 (77)
  Male                         52 (34)       15 (35)    12 (23)
  Age group
   65-74                       40 (26)       11 (26)    19 (37)
   75-79                       43 (28)        6 (14)     8 (15)
  80-84                        40 (26)       17 (40)    14 (27)
[greater than or equal
   to] 85                      29 (21)        9 (21)    11 (21)
Cognitive impairment
  None                         63 (41)       17 (40)    31 (61)
  Mild                         40 (26)       14 (33)    13 (26)
  Moderate                     27 (18)        5 (12)     7 (14)
  Severe                       22 (16)        7 (16)     0 (0)
Use of psychotropic medication
                               34 (22)       13 (30)    15 (29)
No. of diagnoses
  0                            45 (30)       11 (26)    10 (19)
  1                            46 (30)        9 (21)    21 (40)
  2                            40 (26)       16 (37)    10 (19)
[greater than or equal
  to] 3                        21 (14)        7 (16)    11 (21)
No. of medications
  0                            27 (18)        5 (12)     8 (15)
  1-2                          48 (32)       11 (26)    14 (27)
  > 2                          77 (50)       27 (63)    30 (58)

(a) The three groups of subjects are mutually exclusive.




The relationship between recurrent falls and hip fracture and various home hazards is shown in Table II. The age- and sex-adjusted odds ratios (ORs) for recurrent falls were significantly increased (p < 0.05) for only one hazard: hazardous toilet railings (OR: 11.5). The age- and sex-adjusted odds ratios for hip fracture were significantly increased (p < 0.05) for two household areas: internal traffic-ways (OR: 2.7) and the bathroom (OR: 2.3). In addition, nine specific hazards were associated with increased risk of hip fracture: doormats (OR:14.4), floor mats in traffic-ways (OR: 3.5), internal steps (OR:9.1), seating (OR: 3.8), bed-lighting (OR: 3.1), bath-tubs (OR: 3.9), bath-mats (OR: 4.6) and toilets (OR: 5.7). Compared with those with railings judged to be safe, the odds ratios for hip fracture were significantly increased in people with no shower railings (OR: 4.3) or toilet railings (OR: 7.5) and in people with hazardous external step railings (OR: 7.0) or hazardous toilet railings (OR:11.9). These findings were essentially unchanged after using logistic regression to adjust for age, sex, cognitive impairment, use of psychotropic medications, number of recorded medical conditions and number of medications.

[TABULAR DATA II OMITTED]

Hip fracture cases had an average of 6.3 hazards in their homes; recurrent fallers had an average of 4.8 hazards; and non-recurrent fallers had an average of 4.2 hazards (see Table III).

We assessed the association between falls and hazards in sub-groups defined by cognitive impairment. Among cognitively intact subjects, the number of home hazards was the same for fallers and non-fallers; however, cognitively impaired fallers had significantly (p < 0.05) more hazards than cognitively impaired non-fallers (see Table III).
Table III. Number of hazards in the homes of hip fracture
cases, recurrent fallers and non-recurrent fallers(a)
                                Mean no. of
                                home hazards   p value(a)

All study subjects
  Hip fracture cases              6.3           0.001
  Non-hip fracture controls       4.4
  Recurrent fallers               4.8           0.12
  Non-recurrent fallers           4.2
Cognitively impaired subjects
  Recurrent fallers               4.9           0.05
  Non-recurrent fallers           3.9
  Cognitively intact subjects
  Recurrent fallers               4.6           0.98
  Non-recurrent fallers           4.6

(a) See footnote (a) to Table II for definitions of hip fracture cases,
fallers and non-fallers.
(b) p value from t test for difference between means.




Discussion

In this study there were practically no differences in environmental hazards between the homes of people with recurrent falls and the homes of other older people. There was some suggestion, however, that home hazards might increase the risk of falls in people with cognitive impairment.

Our study was conducted among older people referred to a geriatric domiciliary service. Such people tend to be fairly frail and this may explain our failure to find any association between falls and home hazards, as there is some evidence that host factors, not the environment, cause most falls among frail older people [11, 12]. Another possible explanation for the general lack of association between falls and home hazards in our case-control study is that hazards that were involved in falls had been removed or modified by the time of the study home assessment. Finally, this was a relatively small study and so there was limited statistical power to detect all but very strong associations.

We found that the homes of people with a recent hip fracture appeared to be more hazardous than those of people without a hip fracture. However, we are concerned that these findings might be due to biased assessment of hazards in the homes of hip fracture patients. Occupational therapists assessing homes could not be kept 'blind' to whether or not a subject had had a recent hip fracture because a patient's functional status is an important part of judging whether or not hazards are present in that patient's home. This means that home assessors could have had a tendency to call a factor a hazard in the homes of hip fracture cases but not in the homes of other subjects, leading to spurious associations.

One way of minimizing the problem of differential misclassification of exposure in case-control studies is to keep data collectors 'blind' to subjects' case-control status. We are doubtful, however, whether such 'blinding' would improve the validity of case-control studies of home hazards and falls and fractures. The problem is that the existence of a hazard depends in large degree on the functional status of the person in whose home the potential hazard exists. For example, a change in the type of floor covering will be a much greater hazard in the home of a person with Parkinson's disease than in other homes. We would go so far as to suggest that home hazard assessment that ignores the functional status of the person living in the assessed homes is meaningless.

Another limitation of our hip fracture data is that subjects in the comparison group may have been more frail than the hip fracture patients. It is possible that the homes of many of these frail control subjects had been modified to reduce the presence of hazards, resulting in spurious associations between hazards and hip fractures.

Several falls cohort studies have included baseline home assessments. A problem in these studies is that home assessments were done up to a year before falls occurred and it is possible that hazards changed over that time. In particular, hazards may have been modified or removed as a direct result of their identification at the baseline home assessment. Tinetti et al. found no overall difference in the number of hazards in the homes of fallers and non-fallers but bedroom hazards were associated with falls [6]. Nevitt et al. found an increased risk of falls in people who reported that factors like poor lighting and low chairs made daily life difficult but there was no association between falls and other home hazards [7]. However, in subsequent analyses of these data, Northridge et al. found that having multiple hazards in the home was associated with risk of falls in active older people but not in frail older people [13]. Studenski et al. have recently reported an increased risk of falls associated with a higher home hazard score [14].

Three randomized trials involving multifactorial interventions (including home assessment) for falls prevention have recently been published [15-17]. All found that their interventions produced some reduction in risk of falls but the independent benefits of home assessment and modification are impossible to determine because this was just one of the many interventions that participants received.

Assessment of home hazards and recommendations for home modifications have long been part of occupational therapy practice with older people. More recently, public-health professionals have become interested in home safety checklists, with subsequent action to make homes safer, as a way of preventing falls and fractures in elderly people [5-7]. However, the present study, like most previous studies, provides very limited evidence that hazards are an important cause of falls and fractures. We believe that the failure to find the expected strong associations between home hazards and falls is due to the limitations of observational epidemiological studies for investigation of this issue. Cohort studies are problematic because of the long time period between assessment of hazards and occurrence of falls, and case-control studies may be inappropriate because of the difficulties of obtaining unbiased assessments of the presence of hazards. To overcome the difficulties likely to be encountered in any observational study of home hazards, we urge researchers to conduct large randomized trials of home assessment and modifications for the prevention of falls and fractures in the elderly population.

References

[1.] Cummings SR, Black DM, Rubin SM. Lifetime risk of hip, Colles', or vertebral fracture and coronary heart disease among white postmenopausal women. Arch Intern Med 1989;149:2445--8. [2.] Tinetti ME, Speechley M. Prevention of falls among the elderly. N Engl F Med 1989;320:1055-9. [3.] The prevention of falls in later life: a report of the Kellogg International Work Group on the Prevention of Falls by the Elderly. Dan Med Bull 1987;34(suppl 4):1-26. [4.] Tideiksaar R. Preventing falls: home hazard checklists to help older patients protect themselves. Geriatrics 1986; 41:26-8. [5.] Rubenstein LZ, Robbins AS, Schuman BL, et al. Falls and instability in the elderly. FAm Geriatr Soc 1988;26678. [6.] Tinetti ME, Speechley M, Ginter SF. Risk factors for falls among elderly persons living in the community. NEngl,JMed 1988;319:1701-7. [7.] Nevitt MC, Cummings SR, Kidd S, et al. Risk factors for recurrent nonsyncopal falls. JAMA 1989;261:2663-8. [8.] Campbell AJ, Borrie MJ, Spears GF, Jackson SL, Brown JS, Fitzgerald JL. Circumstances and consequences of falls experienced by a community population 70 years and over during a prospective study. Age Ageing 1990;19: 136-41. [9.] Clemson L, Roland M, Cumming R. Occupational therapy assessment of potential hazards in the homes of elderly people: an inter-rater reliability study. Aust Occup The J 1992;39:23 - 6. [10.] Rothman KJ. Modern epidemiology. Boston: Little, Brown & Co., 1986. [11.] Morfitt JM. Falls in older people at home: intrinsic versus environmental factors in causation. Public Health (Lond) 1993;97:115-20. [12.] Northridge ME, Nevitt MC, Kelsey JL. Falls in the elderly in relation to home hazards. (Submitted). [13.] Northridge ME, Nevitt MC, Kelsey JL, Link B. Home hazards and falls in the elderly: the need to consider the health and functioning of the individual. Am J Public Health 1995;85:509-15. [14.] Studenski S, Duncan PW, Chandler J, et al. Predicting falls: the role of mobility and nonphysical factors. J Am Geriatr Soc 1994;42:297-302. [15.] Hornbrook MC, Stevens VJ, Wingfield DJ, et al. Preventing falls among community-dwelling older people: results from a randomised trial. Gerontologist 1993;34:16-23. [16.] Tinetti ME, Baker DI, McAvay G, et al. A multifactorial intervention to reduce the risk of falling among elderly people living in the community. NEnglJMed 1994;331: 821-7. [17.] Wagner EH, LaCroix ZA, Grothaus L, et al. Preventing disability and falls in older adults: a population-based randomized trial. Am J Public Health 1994;84:1800-6.

Authors' addresses L. Clemson, M. Roland Occupational Therapy Department, Westmead Hospital, Westmead, NSW 2145, Australia

R. G. Cumming(*) Department of Public Health and Community Medicine, A27, University of Sydney, Sydney NSW 2006, Australia

(*) Address correspondence to Dr R. G. Cumming

Received 10 August 1995
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Author:Clemson, Lindy; Cumming, Robert G.; Roland, Maryanne
Publication:Age and Ageing
Date:Mar 1, 1996
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