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a Department of Epidemiology and Biostatistics, University of Western Ontario, London, Canada
b Department of Physical Medicine and Rehabilitation, Medical University of South Carolina, Charleston
Rhonda J. Scudds, Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Kow-loon, Hong Kong E-mail: rsrhonda{at}inet.polyu.edu.hk.
William B. Ershler, MD
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Abstract |
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Methods. Questionnaires sent to a sample of community-dwelling seniors included detailed questions about pain; the topics covered pain intensity, frequency, duration and location, use of pain medication, cause of pain, physical disability, depressive symptoms, chronic conditions, and demographic information.
Results. Of the 885 respondents, 644 reported musculoskeletal pain 
. Multiple logistic regression analysis revealed that pain of severe or greater intensity was shown to be significantly associated with disability 
. Pain experienced all or nearly all of the time 
and taking pain medication 
were also shown to be associated with disability. The number of pain locations reported by the respondents was also shown to be significantly associated with disability. The OR for the mean number of pain locations (5.8 locations out of a possible 45) was calculated to be 2.12 (95% CI 1.43 and 3.16).
Conclusion. A thorough pain evaluation and appropriate management of certain aspects of pain may aid in the independent functioning of elderly persons.
THE attention to research on musculoskeletal pain in the elderly population is beginning to increase. With an aging population and a large percentage of elderly persons presenting with pain-related chronic musculoskeletal conditions, research into the effect that pain has on physical disability is necessary. Estimates of the percentage of elderly persons with musculoskeletal pain range from 20% to 71%, depending on the definition used for musculoskeletal pain (1)(2)(3)(4). Similar estimates have been made for the prevalence of physical disability, again based on the criteria used to define physical disability.
The presence of pain has been shown to be related to physical disability (5)(6)(7). However, when the presence of pain was used in the analyses, it was considered to be equal for all subjects. As a result, the relationship between pain and disability may actually be diminished because of the possibility that mild pain, or pain in one area of the body for a short period of time, affects physical disability much less than does severe pain that is present in many locations and present almost all of the time.
Little information is available in the literature about the association between physical disability and specific characteristics of pain—such as pain intensity, frequency, location, and duration—that is especially relevant to the elderly population. In a few studies involving persons with low back pain, the relationship between pain intensity and disability has been examined (8)(9)(10)(11). These studies did not include senior citizens or included only a small percentage of persons aged 65 years or older. However, evidence of a significant positive relationship between pain intensity and disability has been shown in groups of younger people with low back pain.
The primary objective of this study was to determine whether specific characteristics of pain, such as intensity, location, duration, and frequency, are associated with physical disability for people aged 65 years or older who report musculoskeletal pain. Functional independence in the elderly population is important. The data obtained from a sample of senior citizens may provide information about the multidimensional nature of musculoskeletal pain and its possible association with physical disability.
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Methods |
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The main study variables were physical disability, pain intensity, location, duration and frequency, pain medication, and knowledge of the cause of the pain. The presence of a physical disability was evaluated as a categorical variable. A respondent was considered to have a physical disability if he or she reported having at least "some difficulty" with three or more activities. This definition was used to maximize the likelihood that those categorized as having a physical disability were categorized correctly. Also, this definition was used to compare the results of this study with other studies using this criteria (12). The activities listed in the Stanford Health Assessment Questionnaire (HAQ) (13) were incorporated into the questionnaire to examine physical disability. The HAQ was initially designed to assess disability in persons with rheumatoid arthritis (13). However, its use has spread to assess disability in groups of individuals who have other chronic musculoskeletal conditions and in the general population (14). The questionnaire consists of questions about twenty activities in eight different functional categories, including dressing and grooming, rising, eating, walking, hygiene, reaching, gripping, and other activities. The other activities included more complicated tasks such as shopping and household chores. Four possible response categories are listed after each activity: with no difficulty, with some difficulty, with much difficulty, and unable to do. Also, the respondent could report whether help or an aid or device was required to perform the activity.
The presence of musculoskeletal pain was assessed by asking the respondents, "In the last two weeks, have you had any kind of pain in muscles, joints, or bones?" A 2-week period was used in an attempt to minimize recall bias for the specific characteristics of the pain. To assess pain intensity, a 7-point verbal descriptor scale (VDS) was used. The respondents were asked, "In general, how would you describe the level of the pain in your muscles, joints or bones in the last two weeks?" The VDS presented the respondent with the following categories: no pain, slight pain, mild pain, moderate pain, severe pain, extreme pain, and the worst pain imaginable. Elderly persons have been shown to have little trouble with this scale (15), and the VDS has been used to assess pain intensity validly and reliably in the general population (16)(17)(18)(19)(20).
To determine the location of pain, the respondents were asked to shade in the areas on the front and back views of a body diagram. The body diagrams were divided into forty-five areas similar to those described by Toomey and colleagues (21), and pain location was examined by determining the total number of painful areas reported.
The "duration of pain" question included durations of less than 1 year, 1 year to less than 5 years, 5 years to less than 10 years, and 10 years or more. Pain frequency in the past 2 weeks was also assessed by asking the respondents how they would best describe their musculoskeletal pain. The two main categories of responses included whether pain was present all of the time or almost all of the time. The respondents were also asked if they were taking any medication for their musculoskeletal pain and whether they knew the cause of their pain. Both of these variables were dichotomous variables with yes or no as possible answers.
Comorbidity, depressive symptoms, sleep quality, age, sex, marital status, income adequacy, educational level, and living arrangements were also assessed in this questionnaire. These factors have been shown to be related to physical disability and were included in the questionnaire to control for their potentially confounding effects on the associations in question (1)(6)(12)(15)(22)(23)(24)(25)(26)(27). Comorbidity was measured by providing the respondents with a list of 19 medical conditions and asking them if a physician had ever told them that they had any of the conditions. The Center for Epidemiological Studies depression scale was incorporated into the questionnaire to assess depressive symptoms (28)(29)(30). Sleep quality was measured using a 10-cm visual analog scale, with endpoints of "as well as you could imagine" and "as bad as you could possibly imagine," after the respondents were asked how well they had slept, on average, in the last 2 weeks. Age, sex, marital status, income adequacy, and educational level were all assessed as categorical variables.
Analysis
All analyses were performed using SPSS version 6.02 (SPSS, Inc., Chicago, IL). Descriptive statistics were performed, including frequency distributions for categorical variables and means and standard errors for continuous data. The univariate associations between physical disability and each of the individual characteristics of pain, and between physical disability and the potential confounding variables were determined by calculating the odds ratio (OR) for each variable pair and the associated 95% confidence interval (CI). When the independent variable was continuous, the OR per one-unit increase of the variable was calculated. After the univariate analyses, mathematical modeling techniques using binomial logistic regression (31)(32) were performed to examine the association between physical disability and the different characteristics of musculoskeletal pain, adjusting for significant confounding variables.
The model was reduced using a backward elimination method by removing individual variables that were nonsignificant. The difference in the -2 log likelihood values of successive models was used as the criterion for eliminating nonsignificant variables. A variable was eliminated from the model if the chi-square statistic for the difference of the -2 log likelihood values was nonsignificant at an alpha level greater than .05.
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Results |
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. The majority of the respondents were women (63.2%). The average number of chronic conditions reported by the respondents was four 
and approximately 25% of the respondents were classified as having depressive symptoms. The average score for sleep quality was calculated to be 32.5 mm 
A summary of the demographic and clinical characteristics of the sample is displayed in Table 1 .
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compared with a mean of 5.1 
for men.
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and 0.81 
, respectively.
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Multivariate analysis showed that pain experienced all or nearly all of the time was significantly associated with physical disability 
. The other pain variable associated with the presence of physical disability was pain medication. The OR for those taking pain medication was calculated to be 1.64 (95% CI 1.08–2.51). The additional significant variables that remained in the final model, and therefore were adjusted for, consisted of age group, number of chronic conditions, and sleep quality (Table 7 ).
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Discussion |
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Pain intensity was divided into three categories: slight or mild; moderate; and severe, extreme, or worst pain imaginable. Only after pain was rated more intense than moderate did the OR associated with disability increase to approximately 4 in the logistic regression analyses. As mentioned previously, several research studies have shown an association between pain intensity and physical disability, although not in the population of elderly persons (8)(9)(10)(11). It is possible that once a certain perceived level of pain has been reached, its effect on physical functioning becomes more profound. This assumes a causal relationship between musculoskeletal pain and physical disability, an explanation that is biologically plausible but not one that can be concluded from this cross-sectional study.
The number of areas of pain that an individual shaded in on a body diagram was also shown to be significantly associated with physical disability. The more shaded areas, the more likely that he or she had difficulty doing daily activities. No previous research reports have examined this relationship. However, a compounded effect of multiple areas of pain seems likely. It may be important to look at more than simple pain intensity when examining the relationship between pain and disability.
As shown by the study data, many other aspects of pain may play a role in whether a person has difficulty doing particular activities. The frequency of pain was also strongly associated with physical disability. Those persons with pain all of the time or nearly all of the time were at least twice as likely to have a physical disability. It is interesting that moderate pain present all of the time may be just as clinically significant as periods of extreme pain. Although statistically significant, these results may be explained by another factor, such as anxiety or coping strategy. To report having pain all or nearly all of the time may reflect some cognitive or psychological aspect of the pain experience that was not examined in this study.
The duration of pain, although significantly related to physical disability in the univariate analyses, was eliminated from the final multivariate model. It is possible that those who have had pain for a longer period of time are older. Consequently, the age of the respondent may have accounted for the significant relationship between pain duration and disability. However, no significant association was found between duration of pain and age. Disability was shown to increase with aging, which supports several studies that reported similar results (22)(33)(34). With regard to the duration of pain, experiencing longer periods of pain may result in altered and improved coping strategies to deal with the potential effects of physical disability.
Not knowing the cause of pain, even though this approached statistically significant levels in the multivariate model, was also eliminated. This factor, however, may be important clinically in its role in physical disability. Those who do not know the cause of their pain may not have sought explanation for the cause, possibly because the pain was not impacting their physical functioning. On the other hand, knowing the cause of pain may allow a person to deal with the pain better and to implement coping strategies, treatments, or adaptations necessary for maintaining physical functioning. Further research in this area may be warranted.
Those persons who were taking pain medication were more than 1.5 times more likely to have a physical disability. These data, controlling for the other pain variables, imply that another factor, apart from those strictly related to pain, may play a role in this relationship. Experience with pain or the interpretation of pain may influence whether a person takes pain medication and may also influence activities related to pain and the reporting of difficulty with certain activities related to pain. Another possible explanation could be that those who took pain medication actually had higher pain scores, which may have been diluted in the categorization of pain intensity.
Some of the limitations of the study should be mentioned. The data were collected using a cross-sectional design. Consequently, no causal relationships can be concluded from the results. Although associations were found between the presence of a physical disability and pain intensity, location, frequency and medication use, these factors cannot be assumed to cause difficulty with daily physical activities. Further research is required to investigate, in a prospective manner, the effect of pain on physical disability.
An additional potential limitation involves the possible discrepancy between self-report and more objective measures of health status. The study relied on the health perceptions of the respondents. With regard to pain, this should not be a problem because pain is an individual experience and researchers and clinicians alike rely on their subjects' and patients' perceptions of pain. Assessing difficulty with daily activities, however, may be more problematic. Discrepancies between self-reported functional ability and observation of function have been reported (35). However, in Rubenstein and coworkers' (35) study of nursing home residents, subjects tended to overstate their functional abilities. In case a similar overestimation of functional ability occurred in our study, the association between specific pain variables may have been underestimated.
Finally, volunteer bias may have occurred in the study. Although specific, simple instructions were provided that described who should complete the questionnaire, it is possible that those individuals who had pain or those who had preconceived notions about the relationship between pain and disability were more likely to complete the questionnaire.
More than one-quarter of the elderly persons who reported pain described it as severe or present all or almost all of the time, or they shaded in many areas of pain on the body diagram. All of these characteristics of pain were shown to be associated with physical disability. Thorough pain assessment and adequate pain management should be emphasized in this elderly group of individuals. Several recent clinical studies have assessed the effects of exercise programs on pain and disabilty for persons with osteoarthritis, a condition commonly associated with pain in the elderly population (36)(37)(38). These studies have reported reductions in disability and pain and improvements in functional tasks. Additional research, including prospective studies examining the effect of musculoskeletal pain on the development of physical disabilities, should be undertaken. Education and treatment studies, including exercise programs, are also required to determine effective ways of preventing and managing disability and musculoskeletal pain in a variety of conditions associated with pain as well as maintaining or increasing functional independence.
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Acknowledgments |
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Received January 5, 1999
Accepted November 10, 1999
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