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Keywords:

  • Total hip replacement;
  • Elderly;
  • Function;
  • WOMAC;
  • Mental health;
  • Geriatrics;
  • Outcome assessment

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Objective

To determine whether psychosocial factors, chronic diseases, and common geriatric problems are associated with poor physical function 3 years after primary total hip replacement (THR).

Methods

We studied a sample of Medicare recipients in Ohio, Pennsylvania, and Colorado (n = 922) who underwent primary THR in 1995 (mean ± SD age 73.1 ± 5.6 years, 32% men). Participants completed a questionnaire regarding lifestyle factors, medical history, and quality of life ∼3 years after the surgery. Physical function was measured using the function subscale of the Western Ontario and McMaster Universities Osteoarthritis Index. We assessed the relationship between functional outcome 3 years postsurgery and 4 predictor domains: pain or complications in the operated hip, other musculoskeletal comorbidity, medical factors (obesity, chronic medical comorbidity, rheumatoid arthritis, and such common geriatric problems as falls, poor balance, or incontinence), and psychosocial factors (mental health, regular alcohol consumption, smoking, provider role, living alone, and education).

Results

Ten percent of subjects had poor functional status. In a logistic regression model controlling for sex and age, the following factors were associated with an increased risk for poor functional status (in order of importance): pain in the back or lower extremity, severe pain in the operated hip, poor mental health, more than 1 common geriatric problem, obesity, and less than college education.

Conclusion

Pain in the operated hip was strongly associated with poor functional status 3 years after THR. However, other factors associated with poor functional status were not related to the hip. Our results suggest that a comprehensive assessment of functional status in elderly THR patients should include assessment of common geriatric problems, mental health status, and weight.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Osteoarthritis (OA) of the hip is common among older persons (1, 2), and total hip replacement (THR) as a treatment for severe hip OA is performed frequently in this population (3). Previous studies found that preoperative functional status and medical comorbidities are important predictors of functional status following THR (4, 5). However, geriatric indicators of frailty (such as falls, decreased balance, and incontinence) that may occur independent or in addition to medical comorbidities have not been studied in patients undergoing THR, despite their older age.

Drawing from extensive literature on the multidimensional determinants of function in older persons (6–8), we hypothesized that psychosocial factors related to aging, such as poor mental health (9), living alone (10), serving in a role as provider for others (11), lower education (12), as well as geriatric indicators of frailty (7), may be associated with worse functional status 3 years after THR. We further hypothesized that these factors, seemingly unrelated to the operated hip, may be mediated through hip-related factors, such as hip pain.

The objective of this analysis was to investigate whether, and to what extent, poor physical function 3 years after THR is correlated with these factors unrelated to the hip itself.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Data source.

This analysis is based on a questionnaire followup of Medicare beneficiaries who underwent THR during the period of July 1, 1995 through December 31, 1995. Validated case finding algorithms using International Classification of Diseases, Ninth Revision, Clinical Modification and Current Procedural Terminology codes were used to assemble a population-based sample of all Medicare beneficiaries whose claims indicated that they had undergone THR during the study period (13, 14). The algorithm for identifying patients with primary THR was validated against a medical record review in 1,031 patients. The positive predictive value of the algorithm was 99% (15). Subjects younger than 65 years and those with codes indicating infection of the hip, metastatic cancer or bone cancer, conversion of hemiarthroplasty (or other hip surgery) to total hip replacement, and fractures of the hip and femur were excluded. Enrollment in a health maintenance organization was also an exclusion criterion because capitated health maintenance organizations may not reliably submit claims to the Health Care Financing Administration. For similar reasons, beneficiaries not enrolled in both parts A and B of Medicare and those not resident in the United States were excluded. We assembled a random sample of patients in 3 US states (Colorado, Pennsylvania, and Ohio) for detailed study. We chose Colorado, Pennsylvania, and Ohio because these 3 states had rates of THR near the national average and offered a range of urban and rural settings and geographic diversity.

We developed a 2-stage random sampling technique. First, we categorized hospitals according to hospital volume, and randomly chose hospitals in each of 5 volume strata, with probability of selection proportional to size. We then randomly selected patients within each hospital. See Figure 1 for descriptions of response rate and recruitment flow. The 2-stage random sampling technique selected a total of 1,938 patients with primary THR from a cohort of 7,092 primary hip replacements performed on Medicare beneficiaries during the study period in Pennsylvania, Ohio, and Colorado. Of the 1,938 primary THR recipients, 32 (1.7%) had died between the time we chose the sample and the time we contacted patients (6–12 months). Another 20 (1.0%) could not be located because of an incorrect address. Of the 1,886 surviving patients with accurate addresses, 516 (27%) never responded to the 3 letters of invitation, 340 (18%) refused to participate, and 1,031 (55%) agreed to participate. Of these, 957 (93%) returned their questionnaires. Of the 957 subjects, 755 (73%) had complete data and were included in the multivariate analyses.

thumbnail image

Figure 1. Recruitment flow. THR = total hip replacement.

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We used Medicare claims data to compare select characteristics of subjects that refused or never responded to our invitation with those of the participants. In the primary THR cohort, those who refused or never responded were older than subjects who participated (76.2 versus 74.1 years; P = 0.0001). Forty percent of eligible African American patients participated versus 51.3% of white patients (P = 0.03). Also, 34% of patients who were eligible for Medicaid (indicating poverty level income) completed the survey versus 51% of those with higher incomes (P = 0.004). Distributions of responders and nonresponders did not differ with respect to patient sex and whether the patient had a dislocation, deep wound infection, or pulmonary embolus within the 3 years following surgery.

Data elements.

This analysis was restricted to data from a questionnaire sent to eligible responding subjects concerning their current state 3 years after THR.

Physical function, measured by the Western Ontario and McMaster Universities Osteoarthritis Index Likert Version 3.0 (WOMAC) function subscale, was the dependent variable (16–18). The WOMAC is a disease-specific measure that was developed specifically for patients with OA to measure pain, stiffness, and function. We restricted our analysis to the WOMAC function subscale and transformed WOMAC function scores to a 0–100 scale: a WOMAC function score of 100 indicates that the patient has no difficulty with any of the functional activities and a score of 0 indicates that the patient has extreme difficulty with all activities. In between, a score of 25 indicates that a patient has severe difficulty, 50 indicates moderate difficulty, and 75 mild difficulty. We used 50 as a cutoff point to define poor functional status, as this score is characteristic of a patient who has moderate difficulty with all functional activities. Patients evaluated preoperatively before THR generally have WOMAC functional scores close to 50 or below (19, 20). Differences in WOMAC functional scores of more than 10 points on the transformed 1–100 WOMAC scale are generally perceptible to patients (21).

Correlates of postoperative functional status were grouped into different clinical domains.

Hip-related factors.

Index hip pain was derived from an item included in the Harris Hip Score (having none, mild or moderate, or severe pain) (3). In a question regarding complications in the operated hip, we asked for information regarding dislocation, loosening of the prosthesis, or later surgical intervention at the operated hip (none versus ≥1 of these complications).

Other musculoskeletal comorbidity.

Patients reported whether they had had another joint replacement or revision in addition to the index hip, including the contralateral hip and left or right knee (none versus 1 or more). Patients also reported whether in the past 4 weeks their activities were limited by pain or discomfort in the back or lower extremities other than the index hip (no versus yes).

Medical factors.

We assessed age, sex, and obesity (body mass index >30). Patients separately reported chronic diseases in the last 10 years (stroke; cancer; congestive heart failure; heart attack; high blood pressure; diabetes; kidney disease; asthma, bronchitis, emphysema, or other lung disease; ulcer or stomach disease; and anemia or other blood disease). These were summarized as none or 1 versus ≥2. Rheumatoid arthritis was assessed separately (no versus yes). The presence of common geriatric problems was recorded as memory problems or confusion, vision problems, hearing problems, falling down, difficulty controlling bowel or bladder, and poor balance. These were summarized as none, 1, or ≥2.

Psychosocial factors.

Mental health was assessed by the 5-item mental health index from the Short Form 36 Health Survey (22, 23). A score ≤ 60 was used to indicate poor mental health; this is equivalent to the 75th percentile of a population-based group of patients with a diagnosis of clinical depression (24). We asked about college education (no versus yes), whether subjects currently lived alone (no versus yes), were current smokers (no versus yes), or currently drank 2 or more alcoholic drinks per day (no versus yes). Provider role was considered to be present if a family member depended on the participant to do household chores (no versus yes).

Analysis.

Univariate analyses of the associations between the primary outcome (WOMAC score <50) and binary independent variables were conducted using Fisher's exact test and chi-square tests. Odds ratios (OR) and 95% confidence intervals served as measures of effect.

To compute adjusted ORs and 95% confidence intervals, logistic regression models were fit using maximum likelihood estimation. We first calculated intermediate multivariate models within each predefined clinical domain, including statistically significant independent variables from the univariate analysis (P < 0.05). Then we conducted analyses over all domains that included statistically significant variables from the intermediate analysis. All these models were adjusted for sex and age. Because multiple comparisons were made in our models, increased chances of associations were possible. Therefore P values in the multivariate analyses between 0.05 and 0.01 were viewed as borderline significant, whereas P values < 0.01 were reasonable for indicating significance.

The inclusion of hip pain, complications in the index hip, and pain in the back or lower extremity in the models that included variables from all domains could possibly result in overadjustment. This would be the case if any of the factors (for instance, obesity) limited functional status partly by causing hip or back pain. Therefore, we also conducted an analysis that included significant variables from all domains except hip and other musculoskeletal problems. Differences between this analysis and those that included these factors may provide insight into how some variables are correlated with functional status. For example, if a factor is related to function without adjustments for hip and other musculoskeletal variables, but not after such adjustments, there is evidence that the factor operates partly by causing orthopedic problems (hip or back).

A multivariate linear regression analysis with WOMAC function as a continuous dependent variable was constructed to illustrate the effects of the independent variables identified in the overall logistic regression model in terms of points in the WOMAC scale. Age, sex, and all independent variables that reached significance in the univariate analysis were controlled in the analysis. A 5% significance level was maintained throughout these analyses, and all tests were 2-sided. Data were analyzed with SPSS Version 10.0 (Chicago, IL) and SAS Version 8.0 (SAS Institute, Cary, NC).

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Patient characteristics are summarized in Table 1. Forty percent of all subjects were male. The mean ± SD age of participants was 73.1 ± 5.6 years; 32% of subjects were >75 years old. Almost all participants were white (97%). Mean WOMAC function score 3 years after primary THR was 76.9 ± 18.8. Worse functional outcome, defined as WOMAC function score <50, was found in 10.3% of all subjects.

Table 1. Characteristics of patients*
CharacteristicPercentageN
  • *

    BMI = body mass index; MHI-5 = 5-item mental health index from the Short Form 36 Health Survey.

  • Percentage unless otherwise indicated.

  • N is the number of subjects who responded to the question.

  • §

    Provider role indicates whether a family member depended on the participant to do household chores.

Medical  
 Age, mean ± SD (range) years73.1 ± 5.6 (65–93)922
  Older than 75 years32 
 Male40922
 White97914
 Rheumatoid arthritis4922
 Chronic diseases, 0–1/≥270/30922
 Obesity, BMI >3025922
 Common geriatric problems 0/1/≥245/29/26922
Index hip  
 Pain in the index hip: none/mild, moderate/severe58/25/17897
 Complications in the operated hip7922
Other musculoskeletal comorbidity  
 Other joint replacement or other revision39828
 Pain in back or lower extremity60795
Psychosocial  
 Poor mental health, MHI-5 <6012917
 College education21899
 Living alone31922
 Current smoker4916
 Two or more alcoholic drinks daily7914
 Provider role§63885

As expected, hip-related problems were associated with poor functional status (WOMAC function <50). The crude OR for severe pain in the operated hip was 5.6, and that for complications in the operated hip was 2.3 (Table 2). Pain or discomfort in the back or lower extremities had a significant association with worse functional status (OR 10.1). Medical factors significantly associated with poor functional status were obesity (OR 2.4), 2 or more chronic diseases (OR 2.4), and 2 or more common geriatric problems (OR 3.1). Psychosocial factors were significantly associated with poor function status, including poor mental health (OR 4.6) and less than college education (OR 4.1).

Table 2. Predictors of poor functional outcome on the univariate level and adjusted within domains*
CharacteristicCrude OR (95% CI)Adjusted OR (95% CI)
  • *

    Factors not significantly associated with poor outcome in univariate analysis were not included in the adjusted models. OR = odds ratio; 95% CI = 95% confidence interval; BMI = body mass index; MHI-5 = 5-item mental health index of the Short Form 36 Health Survey.

  • Adjusted for age (>75 years), sex, and statistically significant univariate factors within each domain.

Medical  
 Age, >75 years1.3 (0.8–2.0)1.2 (0.7–1.9)
 Female1.3 (0.8–2.0)1.2 (0.7–1.9)
 ≥2 chronic diseases2.4 (1.5–3.6)2.0 (1.3–3.1)
 Obesity, BMI >302.4 (1.6–3.8)2.3 (1.5–3.7)
 1 common geriatric problem1.0 (0.6–1.6)-
 ≥2 common geriatric problems3.1 (2.0–4.8)3.0 (1.8–4.6)
 Rheumatoid arthritis1.7 (0.7–4.3)-
Index hip  
 Mild or moderate pain in the index hip0.8 (0.5–1.4)-
 Severe pain in the index hip5.6 (3.5–8.8)6.2 (3.7–10.3)
 Complications in the operated hip2.3 (1.2–4.4)1.4 (0.7–2.8)
Other musculoskeletal comorbidity  
 Pain in back or lower extremity10.1 (4.3–23.4)9.5 (4.1–22.3)
 Other joint replacement or revision1.5 (1.0–2.4)-
Psychosocial  
 Poor mental health, MHI-5 <604.6 (2.8–7.6)4.0 (2.4–6.7)
 Less than college education4.1 (1.8–10.0)3.7 (1.6–8.8)
 Living alone1.2 (0.8–1.9)-
 Current smoker0.8 (0.2–2.6)-
 ≥2 alcoholic drinks0.8 (0.3–2.0)-
 Provider role0.7 (0.5–1.1)-

Age (investigated continuously, age squared, and binary: old >75 years), sex, joint replacement or revision other than the index hip, being a current smoker, consuming 2 or more alcoholic drinks per day, living alone, and having a provider role were not associated with poor functional status.

Multivariate analysis.

At least 1 factor from each domain was significantly associated with poor functional status in the multivariate analysis (Table 3). All models were adjusted for sex and age.

Table 3. Significant factors associated with poor functional outcome (WOMAC < 50) 3 years after primary THR*
CharacteristicCrude OR (95% CI)Adjusted OR (95% CI)Adjusted OR (95% CI)
  • *

    Both adjusted models included age (>75 years) and sex. WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; THR = total hip replacement; OR = odds ratio; 95% CI = 95% confidence interval.

  • All variables that reached significance in the domain-specific models were entered into the model, except severe pain in index hip, back or lower extremity pain, and complications in the operated hip.

  • All variables that reached significance in the domain-specific models including severe pain in the index hip, back or lower extremity pain, and complications in the operated hip.

Severe pain in index hip5.6 (3.5–8.8)-3.1 (1.8–5.5)
Back or lower extremity pain10.1 (4.3–23.4)-4.8 (2.0–11.80)
Complications in the operated hip2.3 (1.2–4.4)-1.5 (0.6–3.6)
Obesity2.4 (1.6–3.8)2.1 (1.3–3.5)1.9 (1.1–3.3)
≥2 chronic diseases2.4 (1.5–3.6)1.6 (1.1–2.2)1.5 (0.9–2.5)
≥2 common geriatric problems3.1 (2.0–4.8)2.8 (1.7–4.5)2.2 (1.3–3.7)
Poor mental health4.6 (2.8–7.6)3.0 (1.7–5.1)2.1 (1.1–3.9)
Less than college education4.1 (1.8–10.0)3.5 (1.5–8.4)2.7 (1.1–6.7)

In the index hip domain, severe pain in the operated hip was associated with a 6.2-fold increased risk for having a poor functional status. In the domain of other musculoskeletal comorbidity, pain in the back or lower extremities increased the risk of having poor functional status by 9.5-fold. In the medical factors domain, the presence of 2 or more chronic diseases was associated with a 2.0-fold risk for poor functional status and obesity was associated a 2.3-fold risk. Subjects who had 2 or more common geriatric problems had the highest relative risk for poor functional status within the medical domain (OR 3.0). In the psychosocial domain, subjects with poor mental health had a 4.0-fold increased risk for poor functional status. Having less than college education conferred a 3.7-fold risk.

The overall models, including significant correlates from the within-domain analyses, identified 1 hip-related factor (pain in the operated hip) and 5 non–hip-related factors (pain in the back or lower extremities, poor mental health, 2 or more geriatric problems, obesity, and less than college education) as significant factors associated with poor WOMAC functional status. As might be expected, hip pain and pain in the back or lower extremities were the variables most strongly associated with an adverse functional status. However, ORs for all the nonorthopedic factors were at least 1.9 (Table 3).

There was evidence that the effects of these factors were only partly mediated through hip, back, or lower extremity pain, since without adjustment for these orthopedic factors, the ORs for the nonhip variables all increased, but only modestly. Without the adjustment for pain in the hip, back, or lower extremities, having less than college education was the strongest factor associated with poor functional status, with an OR of 3.5 (Table 3).

Table 4 gives adjusted means for estimated WOMAC. The linear regression model and the logistic regression model identified the same independent variables as statistically significant.

Table 4. Adjusted means for estimated WOMAC function*
VariableEstimated WOMAC function
Mean ± SD
  • *

    Estimated WOMAC function is based on a linear regression model. Variables are adjusted for each other and age and sex. WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index; extr. = extremities.

Obesity 
 Yes70.8 ± 12.3
 No79.3 ± 12.0
Common geriatric problems 
 083.2 ± 10.5
 176.1 ± 12.1
 ≥268.6 ± 12.1
Mental health 
 Poor60.6 ± 11.9
 Normal79.1 ± 11.1
College education 
 Yes83.1 ± 10.6
 No75.5 ± 12.7
Pain in the back or lower extr.
 Yes69.6 ± 11.9
 No88.5 ± 11.1
Pain in the index hip 
 None83.0 ± 8.8
 Weak to moderate77.1 ± 9.0
 Severe56.7 ± 7.2

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

Previous studies have identified pain in the operated hip, coexistent disease, and baseline functional status as factors associated with functional outcome after THR (4, 5). As has been conceptualized in geriatric medicine, we hypothesized that functional status reflects multiple dimensions of wellbeing in older persons (5–8). Our findings are consistent with this concept and show that medical, geriatric, and psychosocial factors completely unrelated to the hip correlate with unsatisfactory functional status after primary THR.

The presence of chronic diseases were associated with poor functional status within the medical domain after controlling for age, sex, obesity, rheumatoid arthritis, and common geriatric problems. In the overall analysis, which included significant variables from all domains, this association was attenuated, apparently because some of the effect of chronic diseases is mediated through obesity, geriatric problems, and poor mental health. In a previous study, Greenfield and colleagues showed that a 4-level index of coexistent chronic diseases predicted functional status 1 year after THR after adjustment for sex, age, education, and marital status (4). These findings are consistent with our results. However, the authors did not present results adjusted for mental health, common geriatric problems, and obesity.

Obesity has been identified as a risk factor for the development of OA (25, 26). However, its role in functional status after THR has not been addressed well, other than findings of one study demonstrating an inverse relationship of body mass index and physical activity in patients with hip and knee arthroplasty (27). Our results add evidence that being overweight is associated with worse functional status after primary THR, possibly because of the mechanical stresses on the joint or a relative lack of activity in obese patients.

Mental health has been related to physical functioning in patients with chronic medical conditions (9), but has not been explored in patients having THR. However, in a case analysis of rehabilitation patients, good mental health appeared to help patients benefit from rehabilitation (28). In another small study, Travis and McAuley found that mentally restorative experiences supported the rehabilitation of older persons recovering from hip surgery (29). Several factors might explain the positive association between poor functional status and poor mental health, including reduced activity levels, a reluctance to adopt healthy lifestyles, and greater concern about functional limitations or limited enthusiasm to overcome them.

Education has not been well studied in patients receiving hip replacement. Dexter and Brandt documented that OA patients with more than a high school education received much more comprehensive care than less-educated patients (30), a pattern that could play a role in the better functional status we observed among patients with more education. As education is in part a surrogate of socioeconomic status, this might also indicate that low socioeconomic status is a factor associated with poor functional outcome.

Common geriatric problems have never been investigated regarding their associations with functional outcome in THR patients. Previous studies have shown that age was not an independent correlate of the outcome of total hip and knee replacement (31), findings consistent with our results. However, in our data, the presence of >1 common geriatric problem, such as history of a fall or decreased balance, vision, or hearing, remained a significant correlate of poor functional status even after multivariate adjustment (including age). This indicates that it is not age that matters with respect to poor functional status, but having common geriatric problems. We assume that in some regards, this factor affects functional status indirectly, as markers of frailty. However, some aspects of our geriatric variable may have a more direct impact on poor functional status, such as falls and poor balance.

A limitation of our study is its cross-sectional nature; patient-recorded function was not collected before surgery. This is an aging population whose outcome following THR may be compromised by preexisting or subsequent medical and geriatric-related conditions. This analysis is limited to what conditions are present at the time of the 3-year review and their impact on functional status. Future research needs to include an assessment of geriatric-related risk factors preoperatively to see if these conditions are important in prospectively affecting functional outcome after THR. In addition, the moderately low response rate might have introduced selection bias, because responders may have been more health conscious or have an inherent reason for reporting better functional status than nonresponders. Generalizability is certainly limited to white community-dwelling elderly men and women, and among them to those who were willing to participate in the study. As shown in the Subjects and Methods section, respondents were slightly younger, more likely to be white, and less likely to be Medicaid eligible.

Our report also has several important strengths, particularly its population-based and patient-focused design. We tried to limit recall bias by asking patients to make responses based on the previous 4 weeks, with the exception of the reporting of chronic diseases. Also, the use of self-administered questionnaires may have resulted in more accurate data than interview because of the anonymity of the data collection (32). Finally, we were able to consider multiple domains of possible correlates of poor functional status, including factors that have not been previously studied.

In summary, our study documents the previously unreported finding that non–hip-related factors, including poor mental health, obesity, common geriatric problems, and less than college education, are associated with poor functional status 3 years after primary THR. All of these factors could be addressed in preoperative consultations and postoperative care. Apart from education, they could be modified in comprehensive rehabilitation strategies. Patients should be aware that their functional status may depend not only on their operated hip but also on mental health, weight control, and the correction of common geriatric problems.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES

The authors are indebted to Anne H. Fossel for data management and Elisabeth Wright, PhD, for data programming.

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  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. Acknowledgements
  8. REFERENCES
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