Abstract
Objective
To determine if a previously published model of the influence of self-rated health on physical, mental and social health among patients with joint replacement surgery could be generalized to persons with symptomatic knee OA. Our second purpose was to determine if self-rated health mediated changes in physical, mental and social health.
Methods
Persons with symptomatic knee OA (n = 1,127) who participated in the Osteoarthritis Initiative completed the required measures at baseline, 1-, 2-, and 3-year intervals. The key variable of interest was a single-item self-rated health measure. In addition, measures of physical, mental and social health and a set of covariate measures over the 3-year period were analyzed. Structural equation modeling was used to test interrelationships among variables as well as predictive and mediational relationships among self-rated health and mental, physical and social health after adjusting for baseline covariates.
Results
The full model demonstrated good statistical fit. Prior self-rated health consistently predicted current mental health and social health. Prior social health predicted current self-rated health. Self-rated health also mediated changes in mental health and social health. Only social health changes were mediated by self-rated health over all time periods.
Conclusion
Self-rated health predicts a variety of outcomes of symptomatic knee OA. In addition, self-rated health mediates changes in social health and mental health. The use of self-rated health as a simple and efficient clinical assessment has potential for clinical utility because of its predictive capability and association with multiple health domains.
Self-ratings of general health are among the most commonly used assessments in epidemiological research.1,2 Self-rated health (SRH) is often measured using a single item scale: “In general, would you say your health is…” with possible responses of excellent, very good, good, fair and poor. The construct of SRH appears to represent a synthesis of a patient’s current physical, mental and social health states as well as a general enduring trait representing the individual’s own views of their health along a continuum of healthy to unhealthy.3 Longitudinal studies are needed to test the utility of SRH as physical, mental, and social health conditions change over time following disease or injury.
Perruccio and colleagues found that SRH measurements exhibited elements of changing and stable features in persons undergoing hip and knee arthroplasty over a six-month period following surgery4. They also examined the predictive validity of SRH for inferring current and future physical health, mental and social health constructs in a sample of persons undergoing joint arthroplasty. The authors concluded that SRH was associated with current and future health status and that clinicians should consider adoption of SRH as a clinical measurement to aid in outcome assessment and prognostic and treatment-based decisions for this particular group of patients5.
Most arthroplasty patients experience substantial improvements in a short period of time following surgery.6–8 This is generally not the case for individuals with hip or knee OA who are treated non-surgically. Persons with non-surgically treated arthritis generally report pain and disability that fluctuates, sometimes dramatically, over periods as short as a day9 or over years10–12. It is therefore critical to establish if SRH assessment has potential as a prognostic or outcome measure for persons with symptomatic knee OA.
Single item scales, because of their brevity, are ideally suited for routine use in clinical practice. SRH as a single item scale is unique among brief scales because of the volume of evidence indicating the utility of SRH responses for predicting a broad array of clinically important outcomes from physical, mental and social health3, to societal concerns such as healthcare utilization13,14 and mortality.15 Given that SRH is related to multiple constructs of interest to patients and clinicians and that it is simple to use, the SRH scale appears to have potential as an outcome and prognostic variable for persons with knee OA.
Our primary purpose was to test whether the model proposed and validated by Perruccio and colleagues5 would fit longitudinal data collected from persons with symptomatic knee OA but who did not undergo arthroplasty. If the model proposed by Perruccio et al5 generalized to persons with symptomatic knee OA, the model would be pertinent to a far greater number of patients and clinicians. Our secondary purpose was to determine if self-rated health mediated changes in health status over a 3-year period.
PATIENTS AND METHODS
The Osteoarthritis Initiative
The Osteoarthritis Initiative is a publicly and privately funded prospective longitudinal cohort study of 4,796 persons. A primary objective of the OAI study is to develop diverse cohorts of persons for the study of the natural history, risk factors, onset and progression of knee tibiofemoral OA. The target population, those with or at risk for knee OA based on defined criteria, was recruited using focused mailings of clinical population of persons with OA, newspaper advertisements, presentations at church, civic and community organizations and an educational website about knee OA. The sample is community based to the extent that only 16.8% of persons whose data were used in the current study reported currently seeing a health care professional at baseline.
The OAI study followed three sub-cohorts: incidence, control, and progression. Each subcohort has racially and ethnically diverse mixes of persons between the ages of 45 and 79 years at baseline. The progression subcohort, which was targeted for this study, has 1,390 persons with symptomatic knee osteoarthritis in one or both knees. Persons with symptomatic knee osteoarthritis are defined by OAI investigators as having both of the following in at least one knee at baseline: (a) frequent knee symptoms in the past 12 months, defined as "pain, aching or stiffness in or around the knee on most days" for at least one month during the past 12 months and (b) radiographic tibiofemoral knee OA defined as Osteoarthritis Research Society International (OARSI) atlas grades 1 to 316 which are similar to Kellgren-Lawrence (KL) grades 2 or higher17 as measured on a standardized fixed flexion radiograph. The study was approved by the respective institutional review boards at study sites and written informed consent was provided by all subjects. A complete study design protocol can be viewed at: http://www.oai.ucsf.edu/datarelease/docs/StudyDesignProtocol.pdf
Study Sample
Subjects were recruited from four university-based recruitment centers: (a) the University of Maryland School of Medicine in Baltimore, Maryland, (b) the Ohio State University in Columbus, Ohio, (c) the University of Pittsburgh in Pittsburgh, Pennsylvania, and (d) Memorial Hospital of Rhode Island, in Pawtucket, Rhode Island.
Exclusion criteria were the presence of rheumatoid arthritis, bilateral knee arthroplasty or plans to undergo bilateral knee arthroplasty in the next 3 years, bilateral OARSI stage 3 knee OA, positive pregnancy test, inability to provide a blood sample, use of ambulatory aids other than a single straight cane for more than 50% of the time, co-morbid conditions that might interfere with the 4-year participation, unlikely to reside in clinic area for at least 3 years, current participation in a double-blind randomized controlled trial, unwilling to sign informed consent. In addition, because of the need to track MRI based changes, persons were excluded if they were unable to undergo 3.0Tesla MRI. Accordingly, men weighing more than 130 kgs and women weighing more than 114kg were excluded.
Of 1,390 persons in the OAI progression subcohort, 97 persons underwent either hip or knee arthroplasty during the 3-year follow-up and 166 persons had no repeated measurements. We therefore report results from 1,127 (87.2% of the sample) persons measured at least twice during the 3-year period. Despite a high rate of subject retention over the 3-year period, there was selective loss to follow-up in OAI, a problem common to most cohort studies18. Persons lost to follow-up had greater baseline amounts of activity related pain and physical disability but similar levels of mental health as compared to persons in the progression cohort who were included in our study. Persons lost to follow-up also tended to be male and non-white (See Table 1.
Table 1.
Characteristics of 1,127 persons in the study and 166 persons excluded because of missing data
| Baseline Variables | Persons included in the study Mean (sd) or % (n = 1,127) |
Persons excluded because of missing data Mean (sd) or % (n = 166) |
t-test or chi square p-value |
|---|---|---|---|
| Age | 61.14 (9.13) | 60.97 (9.21) | 0.83 |
| Sex (% female) | 55.6 | 65.6 | 0.015 |
| Race (% Caucasian) | 72.6 | 52.7 | <0.001 |
| Body Mass Index | 30.30 (5.4) | 31.45 (5.6) | 0.05 |
| Comorbidity Score | 0.46 (0.87) | 0.59 (1.16) | 0.17 |
| Self-rated Health | |||
| (1) Excellent (%) | 134 (12.0) | 6 (17.8) | |
| (2) Very good (%) | 488 (43.7) | 51 (31.3) | <0.001 |
| (3) Good (%) | 413 (37.0) | 74 (45.4) | |
| (4) Fair (%) | 76 (6.8) | 29 (17.8) | |
| (5) Poor (%) | 5 (0.4) | 3 (1.8) | |
| CES-D Mental Health | 7.46 (7.47) | 10.04 (10.05) | <0.001 |
| WOMAC Physical Function | 17.51 (12.64) | 23.15 (15.05) | <0.001 |
| KOOS Pain* | 65.88 (18.9) | 58.19 (20.6) | <0.001 |
| KOOS Function and Sports* | 54.66 (26.0) | 49.29 (27.18) | 0.08 |
| PASE Score* | 162.29 (82.36) | 135.18 (91.30) | <0.001 |
Scores for KOOS Pain, KOOS Function and Sports and Physical Activity Scale for the Elderly (PASE) scales increase as symptoms or functional status improves. Scores for WOMAC and CES-D decrease as symptoms or functional status improves. WOMAC is defined as Western Ontario and McMaster Universities Osteoarthritis Index; KOOS is defined as Knee Osteoarthritis Outcome Score; CES-D is defined as Center for Epidemiologic Studies Depression Scale.
OAI Measurements Used in the Current Study
Data for the current study were obtained at the baseline clinic visit and during the 1-year, 2-year and 3-year follow-up visits. The clinical dataset release versions 0.2.2 and 1.2.2, 3.2.1 and 5.2.1 were used (http://oai.epi-ucsf.org/datarelease/About.asp). At all time points, self-rated health (SRH) was measured using the following self-report scale: “In general, would you say your health is…” and the respondent would select from the following options: excellent, very good, good, fair, and poor.
Activity related pain was measured at all time points with the KOOS Pain a 9-item scale that measures extent of pain with common activities such as walking and stair climbing. The scale is scored from 0 (severely painful function) to 100 (no pain with function) and is highly reliable and valid19. The OAI required subjects to complete the scale for each knee. We determined the lowest (greatest pain) score at each time period for the two knees of each subject and used this score for the analysis. The WOMAC Physical Function scale, a reliable and valid scale of activity limitations20, has 17 items and is scored from 0 to 68 with higher scores indicated more severe activity limitations. Again, OAI required subjects to complete a WOMAC for each knee and we used the highest score (worst function) of the two obtained at each time point. To quantify limitation in higher level activities, we used the validated KOOS Function, Sports and Recreational Activities scale21,22, also scaled from 0 to 100 with higher scores indicating higher function. We used these three measures as indicators of a latent physical health variable in the structural equation model described below.
For mental health, we used the Center for Epidemiologic Studied depression (CES-D), a 20 item depression screener scored from 0 (no depressive symptoms) to 60 (severe depressive symptoms). Extensive reliability and validity evidence exists for the CES-D23,24. We used the CES-D as an observed measure of mental health.
We used the Physical Activity Scale for the Elderly (PASE) as a self-report measure of social health. The PASE contains 26 questions that quantify the extent of a person’s leisure activities, household activities and occupational and voluntary activities. The scale has high levels of reliability and validity and reflects a person’s degree of involvement in socially expected roles25,26. The instrument was developed for older adults but has been validated for persons as young as 55 years.27
For covariates we used the following variables: comorbidity28, age, gender, level of education (less than high school, high school, some college, college degree, some graduate training, graduate degree).5 Comorbidity was assessed with a validated self-report instrument developed by Katz and colleagues28. The instrument contains 18 items with 0 to 32 with higher scores indicating greater numbers of comorbid conditions. In addition, we adjusted for race (White vs other) and BMI (kg/m2) because they may influence relationships among health constructs and knee OA29.
Statistical Analyses
The structural equation model (SEM) was specified a priori based on work by Perruccio and colleagues5 and is depicted in Figure 1. Consistent with the prior research5, each consecutive measurement of physical, mental, and social health is mediated by the concurrent SRH across four measurement occasions after controlling for a set of variables. In the SEM, the SRH scores ranging from 1 to 5 were treated as non-normal continuous variable in this study. Specifically, we used the restricted maximum likelihood estimator, also known as Satorra-Bentler test statistic, to obtain the correct fit statistic and standard errors30. Physical health was represented as a latent variable with three indicators. Respective factor loadings were set equal across time to assure invariant measurements of physical health31. All other variables were represented as observed variables. Restricted maximum likelihood method was used to estimate the model to account for non-normal continuous outcome variables. All available data were used during the estimation without resorting to an imputation method to replace the missing values.
Figure 1.
The figure illustrates the longitudinal model from the structural equation modeling. Statistically significant paths are indicated by the solid lines and non-significant paths are indicated by the dashed lines. Covariances are indicated by the curved lines. The covariate box along with the curved lines indicates that both the self-rated health variable and the health status variables at each time point were adjusted for covariates in the final model.
The model simultaneously tested SRH from several perspectives. First, it examined whether prior SRH was associated with current health status, as measured by physical health, mental health and social health. Second, the model examined whether prior health status was associated with current SRH. Third, it examined whether each of the measures in the model was associated with that same measure in the future. Fourth, it examined the association between current health status measures and current SRH. The SRH measures were adjusted for the covariates at baseline and all three follow-up periods. Finally, we tested whether changes in any of the health status measures were mediated by SRH.
We tested changes over three time periods: baseline to 1-year, 1-year to 2-year and 2-year to 3-year. Mplus software32 was used for model fitting. In addition to the significance of model parameters (e.g., path coefficient, factor loading), we tested the statistical significance of particular mediation pathways (e.g., Physical2 -> Self-Rated Health2 -> Physical3).
RESULTS
Descriptive statistics for the baseline and follow-up health status measures and SRH are reported in Table 2. The sample generally showed some improvement in their status from baseline to the 1-year follow-up and then the sample demonstrated minor fluctuations for most measures during the subsequent 2- and 3-year follow-ups with one exception: the social health measure (PASE) showed a consistent trend of worsening over the study period.
Table 2.
Scores for physical, mental and social health and self-rated health measures (n=1,127)
| Health Measure | Baseline Mean (SD) |
1-year Mean (SD) |
2-year Mean (SD) |
3-year Mean (SD) |
|---|---|---|---|---|
| Physical Health | ||||
| WOMAC Physical Function* | 17.5 (12.6) | 15.4 (12.6) | 15.4 (13.0) | 15.8 (13.2) |
| KOOS Pain* | 65.9 (18.9) | 70.9 (19.6) | 70.3 (20.1) | 70.2 (20.6) |
| KOOS Function and Sports* | 54.7 (26.0) | 61.9 (25.6) | 62.1 (25.8) | 60.7 (27.5) |
| Mental Health | ||||
| CES-D-Mental Health Score* | 7.5 (7.5) | 7.6 (8.1) | 7.2 (7.7) | 7.5 (7.8) |
| Social Health | ||||
| Physical Activity Scale for the Elderly* | 162.3 (82.4) | 157.6 (83.1) | 152.5 (82.8) | 147.1 (83.5) |
| Self-rated health | ||||
| (1) Excellent (%) | 12.0 | 9.7 | 9.9 | 8.9 |
| (2) Very good (%) | 43.7 | 42.5 | 40.9 | 43.1 |
| (3) Good (%) | 37.0 | 39.8 | 40.3 | 39.0 |
| (4) Fair (%) | 6.8 | 7.2 | 8.4 | 8.4 |
| (5) Poor (%) | 0.4 | 0.8 | 0.5 | 0.6 |
| Proportion reporting change in self-rated health from previous year |
-- | 34.9% (21.1, 13.8) |
30.5% (15.7, 14.8) |
34.5% (17.4, 17.1) |
| Proportion reporting change in CESD mental health from previous year |
-- | 85.1% (43.6, 41.5) |
83.6% (39.3, 44.3) |
85.6% (45.7, 39.9) |
| Proportion reporting change in PASE from previous year |
-- | 97.6% (52.3, 45.3) |
98.2% (53.2, 45.0) |
97.9% (55.7, 42.2) |
| Proportion reporting change in KOOS Pain from previous year |
-- | 92.7% (35.0, 57.7) |
89.8% (43.0, 46.8) |
88.3% (43.5, 44.8) |
| Proportion reporting change in WOMAC Physical Function from previous year |
93.9% (39.7, 54.2) |
90.6% (44.4, 46.2) |
88.9% (47.9, 41.0) |
|
| Proportion reporting change in KOOS Function and Sports from previous year |
84.3% (31.5, 52.8) |
82.2% (42.9, 39.3) |
84.4% (44.5,39.9) |
Scores for KOOS Pain, KOOS Function and Sports and Physical Activity Scale for the Elderly (PASE) scales increase as symptoms or functional status improves. Scores for WOMAC and CES-D decrease as symptoms or functional status improves. WOMAC is defined as Western Ontario and McMaster Universities Osteoarthritis Index; KOOS is defined as Knee Osteoarthritis Outcome Score; CES-D is defined as Center for Epidemiologic Studies Depression Scale.
For all variables, the proportion reporting change from the previous year is described as a percentage. The numbers in parentheses below each percentage estimate represent the percentage of persons who demonstrated worsening followed by the percentage who demonstrated improvement, accounting for the scoring of each scale.
The value for the Chi Square test of model fit was 1,311.87 (p< 0.001; df=266). Fit indices showed a well fitting model: CFI = 0.944, TLI = 0.924, RMSEA = 0.059 [90% CI = 0.056, 0.062, and SRMR = 0.079). Except for covariates, significant path coefficients are represented by solid directional lines and non-significant paths by dashed lines in Figure 1.
As seen in Table 3 prior SRH predicted current social health during all three time periods and future mental health for one-year and three-year time periods. Prior SRH also predicted current physical health for one-year and two-year time periods. Prior social health predicted current SRH for all three time periods. Prior physical and mental health did not predict current SRH for any time period. Each health status measure in the model (SRH, physical, mental and social health) predicted the same measure in the future for all time periods. Similarly, prior SRH predicted current SRH for all time periods. Current social and mental health predicted current SRH for all time periods while current physical health predicted SRH for only the first year.
Table 3.
Path coefficients for full longitudinal model*
| Baseline | 1-year | 2-year | 3-year | |||||
|---|---|---|---|---|---|---|---|---|
| Timeframe | Standardized Estimate |
P | Standardized Estimate |
P | Standardized Estimate |
P | Standardized Estimate |
P |
| Prior health status predicting current health status | ||||||||
| Physical Health | 0.710 | <0.001 | 0.748 | <0.001 | 0.744 | <0.001 | ||
| Mental Health | 0.643 | <0.001 | 0.704 | <0.001 | 0.678 | <0.001 | ||
| Social Health | 0.601 | <0.001 | 0.608 | <0.001 | 0.647 | <0.001 | ||
| Prior self-rated health predicting current self-rated health | ||||||||
| Self-Rated Health | 0.510 | <0.001 | 0.540 | <0.001 | 0.523 | <0.001 | ||
| Prior self-rated health predicting current health status | ||||||||
| Physical Health | −0.084 | <0.001 | −0.080 | 0.002 | −0.026 | 0.309 | ||
| Mental Health | 0.109 | <0.001 | 0.043 | 0.074 | 0.130 | <0.001 | ||
| Social health | −0.121 | <0.001 | −0.178 | <0.001 | −0.095 | <0.001 | ||
| Prior health status predicting current self-rated health | ||||||||
| Physical Health | 0.006 | 0.871 | −0.067 | 0.080 | −0.014 | 0.716 | ||
| Mental Health | 0.028 | 0.346 | −0.036 | 0.223 | −0.021 | 0.529 | ||
| Social health | 0.137 | <0.001 | 0.153 | <0.001 | 0.175 | <0.001 | ||
| Current health status predicting current self-rated health | ||||||||
| Physical Health | 0.031 | 0.352 | 0.007 | 0.834 | 0.076 | 0.032 | 0.036 | 0.350 |
| Mental Health | 0.218 | <0.001 | 0.135 | <0.001 | 0.161 | <0.001 | 0.129 | <0.001 |
| Social Health | −0.498 | <0.001 | −0.390 | <0.001 | −0.426 | <0.001 | −0.417 | <0.001 |
| Effects of covariates on self-rated health | ||||||||
| Female | −0.014 | 0.544 | −0.024 | 0.236 | −0.032 | 0.098 | 0.014 | 0.517 |
| Comorb | 0.103 | <0.001 | 0.016 | 0.432 | 0.014 | 0.429 | 0.041 | 0.078 |
| White | −0.168 | <0.001 | −0.079 | <0.001 | −0.028 | 0.204 | −0.089 | <0.001 |
| BMI | 0.079 | <0.001 | 0.021 | 0.310 | 0.034 | 0.083 | 0.009 | 0.696 |
Higher scores in physical and social health indicate better health status while higher scores in mental health and self-rated health indicate worse depressive symptoms or worse health.
Covariates showed statistically significant effects at baseline with sex being the only covariate not demonstrating a significant effect. At least one covariate had a significant effect at each time point following the baseline period. After adjusting for prior physical, mental and social health, prior SRH mediated changes in current health, most consistently through mental health and social health (see Table 4. SRH mediated changes in social health at all time periods. Changes in physical health were not mediated by SRH.
Table 4.
Mediation analyses for the model
| Type of Mediation | Standardized Estimate |
P value |
|---|---|---|
| Baseline Physical Health → 1-year Physical Health via Baseline SRH* | −0.003 | 0.371 |
| 1-year Physical Health → 2-year Physical Health via 1-year SRH | −0.001 | 0.836 |
| 2-year Physical Health → 3-year Physical Health via 2-year SRH | −0.002 | 0.382 |
| Baseline Mental Health → 1-year Mental Health via Baseline SRH | 0.026 | <0.001 |
| 1-year Mental Health → 2-year Mental Health via 1-year SRH | 0.006 | 0.079 |
| 2-year Mental Health → 3-year Mental Health via 2-year SRH | 0.021 | <0.001 |
| Baseline Social Health → 1-year Social Health via Baseline SRH | 0.062 | <0.001 |
| 1-year Social Health → 2-year Social Health via 1-year SRH | 0.068 | <0.001 |
| 2-year Social Health → 3-year Social Health via 2-year SRH | 0.040 | <0.001 |
SRH = self-rated health
DISCUSSION
Our interest was in determining whether the model proposed by Perruccio et al5 would generalize to the much larger population of persons with symptomatic knee OA who have not undergone joint replacement surgery. We also examined the extent to which SRH was a determinant and was influenced by a variety of health outcomes. Our model, like that of Perruccio et al, was designed to test the following key associations: 1) whether prior SRH predicted current health status, 2) whether prior health status predicted current SRH, and 3) whether SRH mediated changes in each of the health status measures. These key associations were examined simultaneously in the model while adjusting for the baseline covariates, repeated measures of the same health status and SRH measures, and concurrent associations among the measures.
Our results replicated some findings of Perrucio and colleagues but also differed in several ways. First, our findings were similar in that prior SRH predicted current physical and mental health during two of three time periods but, unlike Perruccio et al, we found that prior SRH predicted current social health at all time periods. Perruccio and colleagues found that prior SRH most consistently predicted current mental health. Lower SRH predicted poorer subsequent health status. Second, we found that prior physical health did not predict current SRH, much like Perruccio and colleagues. However, we found that only prior social health consistently predicted current SRH while Perruccio et al found that only prior mental health predicted current SRH.
Reasons for the differences in our findings in regard to effects of prior SRH or health status on current measures are likely due to the populations under study. Patients undergoing knee arthroplasty face a potentially stressful period of hospitalization and risks associated with a major surgery. The psychological impact of these factors likely increase a patient’s general psychological distress and, following the immediate recovery period, typically experience a substantial reduction in anxiety and depression, as reported by Perruccio and colleagues. For persons in our sample with less severe arthritis, psychological stressors are much less immediate and we observed much smaller changes in psychological status. We suspect this more stable period with no major psychological stressors as seen in our sample potentially explain the more limited role of mental health in our study compared to Perruccio et al. Social health was the only predictor of future SRH in our study. Social health showed a consistent pattern of worsening over the study period whereas the other measures showed only minor fluctuations after the first year. The impact of chronic knee arthritis appears to be greatest on daily interactions within a societal context, such as that measured by the PASE as compared to more proximate effects related to pain or person-level actions such as sitting, standing and walking. Current social health also was more strongly associated with current SRH than physical health in our study. We speculate that social health, a construct that captures a person’s roles and interactions with society is more closely aligned with the SRH construct than the physical and mental health constructs in this population of persons with knee OA.
Arnadottir and colleagues conducted a population-based cross sectional study of 185 community dwelling persons 65 years of age and older to determine which demographic and health related factors predict current SRH33 and reported that the strongest predictors of better SRH were higher scores on a subset of items from PASE and the Late Life Function and Disability Instrument34, another scale designed to measure the extent of a person’s engagement with society, in addition to age and depression status. The work of Arnadottir and colleagues provides additional support for the influence of societal participation on ratings of SRH.
Third, we found that SRH consistently mediated changes particularly in social health and also in mental health but not in physical health. The study of Perruccio et al found that SRH most consistently mediated changes in mental health5. As reported earlier, we suspect that social health was consistently mediated by SRH because of the link between SRH and societal interaction and because PASE measures showed consistent worsening over the study period.
We designed our study to replicate the study of Perruccio and colleagues, to the extent possible given the OAI dataset limitations. Our physical health construct included very similar measures to those used by Perruccio et al5 with the exception of a fatigue measure which was not available in OAI. We used the CES-D depression score to represent the mental health construct. Perruccio and colleagues used separate anxiety, depression and fatigue measures to form their mental well-being construct. Because the CES-D measure has demonstrated moderate to strong associations with both fatigue and general psychological distress35,36, it appears to be a reasonable approximation of Perruccio et al’s mental well being construct5. For social health, Perruccio and colleagues used a variety of measures designed to capture the extent to which the patient completed socially expected roles and tasks. We used a single validated measure of task and role performance, the Physical Activity Scale for the Elderly25,26 which appeared to capture most of the social health dimensions assessed by Perruccio and colleagues5. Finally, covariates showed stronger associations with baseline self-rated health as compared to follow-up which we attribute to the more substantial changes during the first year. Race was most consistently associated with self-rated health over the study period.
In sum, we contend that our statistical model is a reasonable approximation to that reported by Perruccio and colleagues5 and that our findings demonstrate commonalities as well as differences. SRH appears to be a potentially useful outcome and prognostic measure not only for persons undergoing joint replacement surgery but also for the much great number of persons with symptomatic knee OA. Self-reported health mediates changes consistently for both mental and social health.
We concur with Perruccio and colleagues5 who argued for a more common use of SRH assessment both in epidemiological and clinical settings. Given that SRH assessment requires only a single item and a few seconds of a patient’s time, routine use of SRH assessment seems both potentially useful and practical. SRH measurements provide a broad assessment of multiple dimensions comprising overall health. For example, self management training emphasizing behavior change and enhanced self-efficacy along with exercise for persons with symptomatic knee OA improve SRH as well as pain and function37. Disturbed sleep, on the other hand, is associated with worse SRH in persons with symptomatic knee OA.38 Complementing these reports, our findings and those of Perruccio et al5 suggest that SRH assessments can inform the clinician on a wide range of health related behaviors.
Our study has important limitations that warrant discussion. We had a large sample but relatively small numbers of persons at baseline (n=81) with SRH scores of either fair or poor which may reduce generalizability, particularly to persons with poor self-rated health. We also had persons with missing follow-up data generally having worse pain and physical and social health. The missing data may have diluted our findings given that persons lost to follow-up likely would have demonstrated larger fluctuations in symptoms over the study period given that their health was worse at baseline. The loss to follow-up, while common for large sample cohort studies18, may adversely affect the generalizability of our findings.
In conclusion, our study demonstrates the potential utility of SRH assessments for persons with symptomatic knee OA in clinical settings. Our study suggests that a simple-to-use single item SRH measure is predictive of future health status and mediates changes in both mental and social health.
Significance and Innovations.
Self-rated health is a simple single-item clinical assessment that mediates both social and mental health changes in persons with symptomatic knee OA.
The use of a global self-rated health assessment should be considered for routine clinical assessment in patients with knee OA because it is both easy to use and it mediates changes in future mental and social health and predicts future physical, mental and social health.
Footnotes
Financial Support Statement: The authors disclose no financial support or other benefits from commercial sources for the work reported on in the manuscript, or any other financial interests which could create a potential conflict of interest or the appearance of a conflict of interest with regard to the work.
Contributor Information
Daniel L. Riddle, Otto D. Payton Professor of Physical Therapy and Orthopaedic Surgery, Virginia Commonwealth University, Richmond, Virginia, 23298-0224, Phone: 804-828-0234, dlriddle@vcu.edu, Fax: 804-828-8111.
Levent Dumenci, Department of Social and Behavioral Health, Virginia Commonwealth University.
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