Impact of persistent hip or knee pain on overall health status in elderly people: A longitudinal population study

Authors


Abstract

Objective

To investigate hip or knee symptoms in older persons from a longitudinal, population perspective, and to determine the impact of persistent hip or knee pain on general health status over time.

Methods

A postal questionnaire was sent to a random sample of 5,500 individuals ages ≥65 years containing the Short Form 36 (SF-36) general health survey, Lequesne hip and knee indices, and a hip/knee pain severity item. Respondents reporting hip or knee symptoms at baseline received an identical questionnaire 12 months later. Respondents were classified into a persistent pain group with either hip or knee pain at both baseline and followup, and a nonpersistent pain group who reported hip or knee pain at baseline but no pain at followup.

Results

At baseline, 1,305 (40.7%) of 3,210 eligible respondents reported hip or knee pain. At 1 year, 1,072 (82.1%) of 1,305 individuals responded, of whom 820 (76.5%) remained symptomatic (the persistent group). In multivariate analysis, baseline factors identified as strongly related to having persistent pain were maximum Lequesne score (odds ratio [OR] 1.09, P < 0.001), maximum hip/knee pain score (OR 1.61, P < 0.001), and number of painful hip and knee joints at baseline (OR 1.48, P = 0.004). Following adjustment for age, sex, and baseline score, differences in mean SF-36 change scores of the 2 groups were significant for all dimensions except for mental health.

Conclusion

In older persons, a symptomatic hip or knee frequently progresses in terms of worsening symptoms and accrual of other symptomatic hip or knee joints. The impact of persistent symptoms on general health is substantial.

INTRODUCTION

Demographically, individuals over 65 years of age are the fastest growing age group. This population growth has considerable implications for health service and socioeconomic planning during the next 2 decades (1, 2). There has been much debate concerning the extent to which increases in longevity will be offset by increased morbidity at older ages (3). Diseases that are associated with impaired mobility are of particular concern due to their potential to increase social isolation and ultimately to threaten a person's ability to live independently. Irrespective of their precise underlying etiology, symptomatic hips or knees are associated with considerable mobility impairment in elderly persons (4). For these reasons, population studies of the natural history of such problems represent vital pieces of information to the planners of future health and social services.

A number of population-based studies have reported the prevalence of individuals affected by hip or knee pain, or by hip or knee osteoarthritis (OA) specifically (5–11). These studies focus on the hip or the knee, rather than both. Although the age profile of study participants varies between these different studies, all nevertheless agree that the prevalence of hip or knee disease is highest among those who are older than 65 years of age.

Although much information is now available concerning the prevalence of hip and knee symptoms in elderly persons, less is known about the natural history of such problems. There are a number of reasons for this. One is that studies of hip or knee problems vary regarding the definition of the problem, or take as their starting point different stages in the care pathway. Different studies therefore also tend to consider different subgroups of the population, so that, for instance, clinically-based studies will naturally exclude individuals with hip or knee symptoms who have not sought help. Understanding the natural history of painful hip or knee conditions is also limited by the fact that such symptoms may be caused by a number of different diseases or acute injuries, with different likely outcomes. In contrast, studies that are based upon specific confirmed diagnoses, e.g., OA, are limited because they generally exclude individuals with hip or knee symptoms that do not appear to have the particular underlying disease of interest.

For all of these reasons, there is a dearth of longitudinal, population-based information of older persons with hip or knee symptoms. Such studies do well to focus on both joints because elderly persons with hip or knee symptoms frequently have more than one symptomatic joint (12).

This report describes findings from a longitudinal survey of hip and knee symptoms in elderly persons. The current study has 2 main goals, to examine the 12-month course of hip and knee symptoms among a cohort of individuals who reported hip or knee pain at baseline, and to assess the impact of persistent hip or knee pain on general health status over time.

PATIENTS AND METHODS

Local research ethics committee approval was obtained for the study (Applied and Qualitative Research Ethics Committee reference A01.060).

Study population.

A random sample of 5,500 Oxfordshire residents, ages 65 years and older, was obtained from the Oxfordshire Health Authority register representing January 2002. Full details concerning the sample size calculations are provided elsewhere (12). A postal questionnaire and cover letter were sent to all participants within a 2-week period in April 2002 and followed up with 2 postal reminders (including a second copy of the questionnaire). Respondents who reported hip or knee symptoms at baseline were sent an identical followup questionnaire 12 months later.

Questionnaire.

The questionnaire was divided into a general section, a hip section, and a knee section. The general section contained a small number of demographic items and the anglicized version of the Short Form 36 (SF-36) general health questionnaire (13). The SF-36 contains 36 items and is widely used as a generic health status instrument. It provides scores on 8 dimensions: physical functioning, role limitations due to physical problems, bodily pain, social functioning, general mental health, role limitations due to emotional problems, energy/vitality, and general health perceptions representing the last 4 weeks. There is also an item that addresses health change during the last 12 months: “Compared to one year ago, how would you rate your general health now?” Scores for each dimension range from 0 (poor health) to 100 (good health).

The hip section began with a screening question using a modified version of the question used in the National Health and Nutrition Examination survey (14), which has also been used in other studies: “During the past 12 months, have you had pain in or around either of your hips on most days for 1 month or longer?” (6, 9–11). Respondents who reported symptoms were asked additional questions about their hip problem, including: “Do you know the cause of your hip pain?”

Severity during the last 4 weeks was assessed separately for the right and left hip using the hip and knee disability indices defined by Lequesne et al (15, 16). This produces a composite measurement score ranging from 1 to 24 points based on 11 items concerned with the presence of pain, discomfort, maximum walking distance, and ability to function. Patients were also asked to rate pain severity in each hip during the last 4 weeks on a scale ranging from “none” to “very severe.” Information regarding the presence of serious comorbidity was assessed using the question: “Do you currently have another health problem that is at least as bad as the problem with your hip?”

The corresponding knee section of the questionnaire was identical to the hip section except that the word “knee” substituted for the word “hip,” and 5 items differed in the Lequesne index. The order of the hip and knee sections was reversed in half of the questionnaires to ensure that the completion rate for the screening question in each section was not biased by its position in the questionnaire. The followup questionnaire was identical to the baseline questionnaire.

Statistical analysis.

Pearson's chi-square test was used to test for differences in baseline characteristics between respondents to the followup questionnaire and those lost to followup. Respondents with followup data were classified into 2 groups for analysis: a persistent pain group who reported either hip or knee pain at both baseline and followup survey, and a nonpersistent pain group who reported hip or knee pain at baseline but no pain at follow-up. Three severity groups, conforming to the threshold values suggested by Lequesne et al (15), were defined separately for the hips and knees: a mild-moderate group (Lequesne score 1–7), a severe group (Lequesne score 8–13), and an extremely severe group (Lequesne score ≥14). Similarly, 3 pain groups (based on the pain severity item) were defined as mild, moderate, and severe. When respondents reported bilateral symptoms, the most severe and most painful joint was used for these classifications.

The association of various sociodemographic, general health, and joint-specific characteristics with having persistent hip or knee pain at followup was examined using Pearson's chi-square test. Factors with a P value less than 0.2 in the univariate analysis were evaluated in a multivariate logistic regression model to investigate which factors were most strongly predictive of persistent pain. General mobility items (taken from the Lequesne index) were not included in the model in order to avoid collinearity. Model fit was assessed using the Hosmer and Lemeshow goodness-of-fit test, and the classification statistic (proportion of observations correctly classified) was computed (17).

The 8 dimensions of the SF-36 were calculated for the persistent and nonpersistent groups at baseline and at followup. The mean change scores for each dimension were calculated and found to be normally distributed for both groups. Analysis of covariance was used to estimate the difference in the group mean change scores. This analysis included an adjustment for the patients' baseline scores to correct for the phenomenon of regression to the mean (18, 19). All analyses were conducted using STATA version 8.0 (Stata, College Station, TX).

RESULTS

Self-reported symptomatic hips and knees at baseline and followup.

Of the 5,500 individuals originally selected, 119 patients (2.2%) were deceased and 342 patients (6.2%) were no longer living at the given address. Of the remaining 5,039 eligible participants, 1,348 (26.8%) did not respond, 201 (4.0%) were unable to participate, and 149 (3.0%) declined participation. Therefore, 3,341 (66.3%) individuals completed and returned the initial questionnaire. Age- and sex-specific response rates varied as follows: of respondents ages 65–74 years, 73.1% were women and 70.6% were men; of respondents ages 75–84, 62.3% were women and 68.3% were men; and of respondents ages 85 years and older, 43.9% were women and 54.5% were men.

Figure 1 shows the study flow of participants based on their response to the screening question at baseline and at 1-year followup. At baseline, 263 (8.3%) of 3,175 respondents reported hip pain only, 695 (21.8%) of 3,194 reported knee pain only, and 347 (11.3%) of 3,076 reported hip and knee pain. Overall, 1,072 (82.1%) of 1,305 symptomatic individuals had responded at 1-year followup, with no difference in the response rates between the 3 baseline groups (hip pain only, knee pain only, hip and knee pain; P = 0.27). Table 1 shows the baseline sociodemographic and other characteristics of respondents at 1-year followup versus those patients lost to followup.

Figure 1.

Study flow diagram based on response to screening question at baseline and 1-year followup.

Table 1. Baseline characteristics of respondents at 1-year followup compared with respondents lost to followup*
 Lost to followup No./total (%)1-year followup No./total (%)P
  • *

    Totals < 233 in lost to followup group, or < 1,072 in 1-year followup group indicate missing values for a characteristic.

  • Pearson's chi-square test.

Age group, years   
 65–7498/233 (42.1)620/1,072 (57.8) 
 75–8492/233 (39.5)383/1,072 (35.7)< 0.001
 ≥8543/233 (18.5)69/1,072 (6.4) 
Sex   
 Male89/233 (38.2)452/1,072 (42.2) 
 Female144/233 (61.8)620/1,072 (57.8)0.27
Lives alone  0.002
 Yes91/221 (41.2)318/1,047 (30.4) 
Homeowner  < 0.001
 Yes137/217 (63.1)810/1,036 (78.2) 
Education   
 Have school qualifications62/217 (28.6)370/994 (37.2)0.02
 Have a degree18/213 (8.5)120/969 (12.4)0.11
 Have professional qualifications37/207 (17.9)252/967 (26.1)0.01
Current regular smoker   
 Yes24/219 (11.0)67/1,020 (6.6)0.02
Body mass index ≥30 (obese)   
 Male15/82 (18.3)59/424 (13.9)0.30
 Female30/128 (23.4)126/580 (21.7)0.67
Severity group at baseline (Lequesne)   
 Mild-moderate32/156 (20.5)276/829 (33.3) 
 Severe58/156 (37.2)332/829 (40.1)< 0.001
 Extremely severe66/156 (42.3)221/829 (26.7) 
Pain score group at baseline   
 Mild56/187 (30.0)329/947 (34.7) 
 Moderate82/187 (43.9)403/947 (42.6)0.38
 Severe49/187 (26.2)215/947 (22.7) 
Other health problems at least as bad as hip/knee problem   
 Yes99/158 (62.7)494/830 (59.5)0.46

Hip and knee symptoms reported at followup are shown in the final stage of Figure 1. Of the 1,072 symptomatic individuals who responded to the second questionnaire, a total of 820 (76.5%) remained symptomatic (the persistent pain group), and 252 (23.5%) reported no hip or knee pain (the nonpersistent pain group) at 1-year followup. Among individuals who had reported hip pain only at baseline, 83 (37.4%) of 222 had no reported hip pain at followup and 38 (17.1%) of 222 reported both hip and knee pain. Among individuals who had reported knee pain only at baseline, 164 (28.6%) of 574 had no reported knee pain at followup and 38 (12.0%) of 574 reported both hip and knee pain. The majority of respondents reporting both hip and knee pain at baseline remained symptomatic in at least 1 joint type at followup (238 [86.2%] of 276 respondents).

The proportion of respondents reporting hip or knee pain was the same at both baseline and followup, regardless of whether the hip or knee section was positioned first in the questionnaire (P > 0.2 in all cases).

Factors associated with persistent hip or knee pain.

The characteristics of individuals in the persistent pain group compared with those in the nonpersistent pain group are presented in Table 2. Sex, smoking status, and additional health problems were not significantly associated with having persistent hip and knee pain in univariate analyses (P > 0.2); therefore, these factors were not included in the multivariate model. All other variables in Table 2 with P > 0.2 were included except for the general mobility items (which form part of the Lequesne index already included in the model). Factors identified in the multivariate analysis that were most strongly related to having persistent pain were maximum baseline Lequesne score (odds ratio [OR] 1.09, 95% confidence interval [95% CI] 1.04–1.14, P < 0.001), maximum baseline pain score (OR 1.61, 95% CI 1.31–1.99, P < 0.001), and number of painful hip and knee joints at baseline (OR 1.48, 95% CI 1.13–1.93, P < 0.004). The Hosmer-Lemeshow goodness-of-fit test indicated a satisfactory model fit (P = 0.45), and the percentage of observations correctly classified by the model was 79%.

Table 2. Baseline characteristics of people with persistent hip or knee pain compared with those who did not have symptoms at 1-year followup*
CharacteristicsNonpersistent hip or knee pain No./total (%)Persistent hip or knee pain No./total (%)P
  • *

    Totals < 252 in nonpersistent group, or < 820 in persistent group indicate missing values for a characteristic. IQR = interquartile range.

  • Unless otherwise indicated, P values determined by Pearson's chi-square test.

  • By Wilcoxon rank-sum test.

Age group, years  0.007
 65–74167/252 (66.3)453/820 (55.2) 
 75–8470/252 (27.8)313/820 (38.2) 
 ≥8515/252 (6.0)54/820 (6.6) 
Sex  0.74
 Male104/252 (41.3)348/820 (42.4) 
 Female148/252 (58.7)472/820 (57.6) 
Lives alone65/247 (26.3)253/800 (31.6)0.11
Is a homeowner208/245 (84.9)602/791 (76.1)0.004
Education   
 Have school qualifications99/231 (42.9)271/763 (35.5)0.04
 Have a degree39/231 (16.9)81/738 (11.0)0.02
 Have professional qualifications72/230 (31.3)180/737 (24.4)0.04
Current regular smoker14/241 (5.8)53/779 (6.8)0.59
Body mass index ≥30 (obese)   
 Male11/97 (11.3)48/327 (14.7)0.40
 Female20/141 (14.2)106/439 (24.2)0.01
Other health problem(s) at least as bad as hip/knee problem101/176 (57.4)393/654 (60.1)0.52
Joints affected at baseline  < 0.001
 Hip(s) only69/252 (27.4)153/820 (18.7) 
 Knee(s) only145/252 (57.5)429/820 (52.3) 
 Both hip(s) and knee(s)38/252 (15.1)238/820 (29.2) 
Number of joints (hips and knees) affected at baseline  < 0.001
 1163/252 (64.7)360/815 (44.2) 
 274/252 (29.4)345/815 (42.3) 
 3 or 415/252 (6.0)110/815 (13.5) 
Severity group at baseline (Lequesne)  < 0.001
 Mild-moderate94/169 (55.6)182/660 (27.6) 
 Severe56/169 (33.1)276/660 (41.8) 
 Extremely severe19/169 (11.2)202/660 (30.6) 
Pain score group at baseline  < 0.001
 Mild117/211 (55.5)212/736 (28.8) 
 Moderate78/211 (37.0)325/736 (44.2) 
 Severe16/211 (7.7)199/736 (27.0) 
Used painkillers for hip/knee pain in last 4 weeks53/174 (30.5)358/663 (54.0)< 0.001
Months since onset of hip/knee problem, median/total (IQR)24/125 (12–84)60/480 (24–120)< 0.001
Maximum distance can walk is <100 yards10/178 (5.6)70/689 (10.2)0.06
Use a walking aid45/207 (21.7)268/739 (36.3)< 0.001
Cannot go up and down a flight of stairs6/210 (2.9)31/740 (4.2)0.38

Change in overall health status over a period of 1 year.

The mean change scores for the SF-36 dimensions are reported in Table 3. The individuals in the persistent pain group had baseline scores that were consistently lower (poorer) than those in the nonpersistent pain group across all dimensions. The mean change scores for the persistent pain group were all negative values, indicating that the overall health status in this group had deteriorated over the course of the year, whereas most of the mean change scores for the nonpersistent pain group were positive, suggesting an improvement in most aspects of general health. The estimated differences in the mean change scores of the 2 groups, adjusting for age, sex, and baseline score, were significant for all dimensions except for mental health. A negative difference in mean change score indicates that the persistent pain group experienced more deterioration and less improvement in health compared with the nonpersistent pain group over the 1-year period.

Table 3. Change in SF-36 scores of participants with persistent hip or knee pain compared with those who did not have symptoms at 1-year followup*
SF-36 dimension Nonpersistent hip or knee pain (n = 252) Mean ± SDPersistent hip or knee pain (n = 820) Mean ± SDEstimated difference in mean change scores (95% CI)P
  • *

    SF-36 = Short Form 36; 95% CI = 95% confidence interval.

  • People with missing values for an SF-36 dimension at baseline or followup were excluded from the analysis.

  • Analysis of covariance adjusted for age, sex, and baseline score. Negative differences in mean change scores imply that the persistent pain group experienced more deterioration/less improvement in general health than the nonpersistent pain group over 1-year period.

Physical functionBaseline64.5 ± 26.449.7 ± 28.7  
 Followup65.5 ± 26.746.0 ± 28.5  
 Change0.97 ± 20.1−3.7 ± 15.7−7.3 (−10.2, −4.3)< 0.001
Role limitation (physical)Baseline62.0 ± 41.147.1 ± 43.2  
 Followup67.3 ± 38.940.4 ± 41.9  
 Change5.3 ± 39.1−6.8 ± 41.1−18.8 (−24.3, −13.2)< 0.001
PainBaseline64.0 ± 22.851.4 ± 23.3  
 Followup71.8 ± 21.849.9 ± 22.6  
 Change7.8 ± 22.4−1.6 ± 20.1−14.7 (−17.4, −11.9)< 0.001
Social functionBaseline83.8 ± 22.173.2 ± 28.9  
 Followup83.9 ± 24.671.0 ± 29.0  
 Change0.15 ± 21.3−2.3 ± 23.8−5.7 (−9.0, −2.5)0.001
Mental healthBaseline78.1 ± 16.675.5 ± 16.7  
 Followup78.0 ± 15.474.9 ± 16.7  
 Change−0.14 ± 14.0−0.59 ± 14.0−1.4 (−3.3, 0.62)0.18
Role limitation (emotional)Baseline84.0 ± 29.774.2 ± 39.0  
 Followup80.3 ± 33.869.8 ± 41.1  
 Change−3.7 ± 36.2−4.5 ± 39.9−5.3 (−10.8, 0.10)0.05
Energy and vitalityBaseline56.8 ± 18.750.2 ± 20.3  
 Followup57.4 ± 19.148.8 ± 20.2  
 Change0.65 ± 13.7−1.4 ± 14.7−3.6 (−5.9, −1.3)0.002
General health perceptionBaseline62.3 ± 18.557.6 ± 20.1  
 Followup63.5 ± 19.357.1 ± 19.4  
 Change1.2 ± 14.0−0.54 ± 13.5−2.7 (−4.8, −0.70)0.009

These findings were also largely reflected in the SF-36 item that asks about health change in the previous 12 months. Among the respondents with persistent hip or knee pain, 68 (8.5%) of 802 regarded their health as better, 511 (63.7%) of 802 thought their health was the same, and 223 (27.8%) of 802 thought their health was worse than the year before. The corresponding proportions for those who were not symptomatic at followup were 39 (16.1%) of 243 respondents, 164 (67.5%) of 243 respondents, and 40 (16.5%) of 243 repondents, respectively. The difference between the 2 groups was significant (P < 0.001, Pearson's chi-square test).

DISCUSSION

In a previous analysis, our findings showed that ∼40% of persons age ≥65 years have hip or knee pain lasting 1 month or more in a given year, and that symptoms frequently affect more than 1 joint, usually involving both legs (12). In addition, in cross-sectional analyses, a significant dose-response relationship was demonstrated in that study for worsening general health status, according to the number of weight-bearing joints that were reported to be symptomatic.

Our current analysis reports longitudinal findings from the same study, which evaluated individuals at 12-months' followup who had symptomatic hips or knees at baseline.

Our analysis revealed that of those respondents who reported hip or knee pain at baseline, 76.5% remained symptomatic 12 months later. Approximatley 14% of the respondents who had hip or knee pain only at baseline reported having pain in both types of joints 12 months later.

In a multivariate analysis, factors found to be strong predictors of hip or knee pain persisting for at least 1 year included the severity of symptoms and disability reported at baseline (Lequesne and pain score of the most severe joint) and the total number of hip and knee joints that were symptomatic at baseline.

A striking finding was that hip or knee pain that had persisted for at least one year led to a significant difference in an individual's general health within that time period (as measured by the SF-36 general health survey instrument), compared with the general health status of individuals whose hip and knee symptoms had resolved within that same year. This was the case for all health status dimensions (with the exception of mental health), although the most striking difference was the effect on physical role limitation and pain dimensions. Nevertheless, although the evidence presented here is consistent with causal direction (from persistent joint pain to worsening broader aspects of health), we cannot rule out the possibility that in some individuals, hip or knee symptoms reported at baseline represented only 1 element of a more widespread condition that was associated with general decline over the course of a year.

There are a number of limitations to this study. The first concerns our definition of persistent pain, because reported hip or knee pain could theoretically have lasted for only 1 month in the year preceding the baseline questionnaire and for 1 month during the followup year. We are therefore unable to specify in detail whether the pain in each symptomatic individual was recurrent, episodic, or chronic/incessant.

A second limitation concerns the respondent's response rates. Study respondents at baseline had a relatively young age distribution for individuals ages 65 and older. In particular, there was a low initial response rate in elderly women, although we did adjust for age and sex in the analysis of the SF-36 scores. Further bias in this regard was introduced at followup, as nonrespondents to the followup questionnaire were more likely to be in the oldest age group, to live alone, and not to be a home owner. They also appeared to be less educated, more likely to be regular smokers, and more likely to have more severe hip and knee pain at baseline. It is likely that many of those lost to followup had died before the followup questionnaire was sent out, but we were unable to confirm this possibility.

Large-scale population studies of health status in elderly persons are uncommon in the UK, particularly longitudinal studies. Based on this methodology, this study contributes additional information to the understanding of joint problems and mobility in elderly persons. Our sample is broadly representative of elderly persons in southeast England. This area is also somewhat more affluent than the UK as a whole (12).

Two particular findings emerged that are worth emphasizing because they have implications for further research or for health and social care provision. The first is that individuals ages ≥65 years who have 1 symptomatic hip or knee joint frequently progress, not only in terms of worsening symptoms affecting the index joint, but also in terms of the accrual of other symptomatic hip and knee joints. Reasons why additional joints become symptomatic are likely to relate to underlying etiology and specific associated risk factors (although the relationship between advanced age and prevalence of symptomatic arthritis, for instance, is not well understood at present) (4, 20–22), but other possible reasons may include the presence of behavioral factors (such as reduced levels of exercise) (23) and psychological factors (24). Such considerations were beyond the scope of this study. However, in terms of maintaining mobility and independence, the reasons why the number of symptomatic weight-bearing joints tends to increase in some elderly persons and not in others warrant further research, together with research into potential interventions to prevent or slow down this process.

The second main finding was that even during 1 year, the impact of having persistent hip or knee pain on a person's overall general health is substantial in the elderly compared with individuals whose hip or knee symptoms resolve, and that improvements in overall general health can be demonstrated in those whose hip and knee symptoms disappear. This finding is supported by evidence from other studies that show that decrements in lower extremity impairment are a significant predictor of disability in activities of daily living (4, 25).

Our findings indicate that improved pain care for symptomatic hips and knees, or more rapid access to joint replacement surgery, could substantially improve the quality of life of many elderly persons, and possibly slow down the accrual of further lower joint problems. With a rapidly increasing elderly population, we need to invest in resources that help to prevent, treat, or at least minimize hip and knee symptoms because they are widespread and persistent in this age group and will increasingly represent a huge burden to the National Health Service and to society as a whole.

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