Abstract
Objective
Previous studies suggest that higher mindfulness is associated with less pain and depression. However, the role of mindfulness has never been studied in knee osteoarthritis (OA). We evaluate the relationships between mindfulness and pain, psychological symptoms, and quality of life in knee OA.
Method
We performed a secondary analysis of baseline data from our randomized comparative trial in participants with knee OA. Mindfulness was assessed using the Five Facet Mindfulness Questionnaire. We measured pain, physical function, quality of life, depression, stress, and self-efficacy with commonly-used patient-reported measures. Simple and multivariable regression models were utilized to assess associations between mindfulness and health outcomes. We further tested whether mindfulness moderated the pain-psychological outcome associations.
Results
Eighty patients were enrolled (60.3±10.3 years;76.3% female, body mass index:33.0±7.1kg/m2). Total mindfulness score was associated with mental (beta=1.31,95% CI: 0.68,1.95) and physical (beta=0.69,95% CI:0.06,1.31) component quality of life, self-efficacy (beta=0.22,95% CI:0.07,0.37), depression (beta=-1.15,95% CI:-1.77,-0.54), and stress (beta=-1.07,95% CI:-1.53,-0.60). Of the five facets, the Describing, Acting-with-Awareness, and Non-judging mindfulness facets had the most associations with psychological health. No significant association was found between mindfulness and pain or function (P=0.08-0.24). However, we found that mindfulness moderated the effect of pain on stress (P=0.02).
Conclusion
Mindfulness is associated with depression, stress, self-efficacy, and quality of life among knee OA patients. Mindfulness also moderates the influence of pain on stress, which suggests that mindfulness may alter the way one copes with pain. Future studies examining the benefits of mind-body therapy, designed to increase mindfulness, for patients with OA are warranted.
Keywords: Osteoarthritis, Mindfulness, Chronic Pain, Psychological Stress
Introduction
Mindfulness is the ability or practice of maintaining a non-judgmental state of heightened awareness of one's thoughts, emotions, or experiences on a moment-to-moment basis.1, 2 The last fifteen years have seen a surging interest in mindfulness as a therapeutic modality that may foster improved health outcomes for patients with chronic pain.3-10 Previous studies have found that higher levels of mindfulness in chronic pain patients were associated with lower self-reported pain7, 9, 11-13 and better pain coping perceptions.3, 14-20 In addition, a recent meta-analysis revealed that interventions promoting mindfulness significantly reduced pain intensity and pain disability in chronic pain patients.3 Mindfulness has recently been characterized as a multidimensional construct of five distinct facets: Observing, Describing, Acting with awareness, Non-judging, and Non-reacting. By analyzing mindfulness at the singular facet level, researchers attempt to further examine psychological mechanisms through which mindfulness specifically contributes to improved health.2, 14, 21 In chronic pain patients, however, only a few studies have utilized this multidimensional approach to assess mindfulness.22-24
Whether mindfulness plays a role specifically in non-surgical patients with symptomatic knee osteoarthritis (OA) has never been examined. Knee OA is the most common cause of disability and joint pain in adults,24, 25 and is primarily characterized by chronic pain which is exacerbated by central sensitization,26, 27 and reduced physical functioning. In addition, patients with OA often suffer from comorbid depression 28 and anxiety, and significantly worse quality of life.29, 30 Although interventions that promote mindfulness skills have repeatedly resulted in improved psychological outcomes for other chronic pain patient groups,7, 12, 13, 31 the underlying mechanism of change remains unclear, and no studies have yet assessed the way mindfulness relates with parameters of physical and psychological health in patients with knee OA. In order to examine the disease-modifying mechanisms of mind body medicine treatments in this population, it is important to understand how mindfulness associates with various, relevant health outcomes. This type of knowledge is also important for optimizing the clinical decision-making process for knee OA patients.
The goal of this study is to examine how mindfulness and its facets are associated with pain, physical, and psychological health measured with commonly-used outcome tools in a chronic pain population with symptomatic knee OA. We further investigate for evidence of pain coping effects using interaction analyses of mindfulness on pain-psychological health associations. We hypothesize that higher total mindfulness and 1 or more individual facets of mindfulness will be associated with less pain, less depression, less stress, better self-efficacy and quality of life. We also hypothesize that mindfulness can moderate the influence of pain on psychological health.
Method
Study design
This study was a cross-sectional, secondary analysis performed on baseline data that was collected for a single-center, 52-week, randomized comparative effectiveness trial of Tai Chi vs. standard physical therapy for adult patients with knee OA. Detailed description of the recruitment and enrollment criteria for this trial has been previously published.32
Participants were recruited from the Greater Boston metropolitan area through advertisements using print media, social media, and the rheumatology clinic patient database at Tufts Medical Center. Inclusion criteria included: 1) age ≥ 40 years, 2) fulfillment of the American College of Rheumatology criteria for knee OA, and 3) Western Ontario and McMaster Osteoarthritis Index (WOMAC) pain score ≥ 40. Exclusion criteria included: 1) prior experience with complementary medicine or physical therapy programs for knee OA within the past year, 2) severe medical limitations precluding full participation, 3) intra-articular steroid injections or surgery in the past three months, 4) intra-articular hyaluronic acid injections in the past six months, 5) Mini-Mental Status examination score <24, or 6) inability to walk without an assistive device. All participants signed an informed consent form before enrollment, and the study was approved by the Tufts Medical Center Institutional Review Board.
Outcome measures
The collection of FFMQ data was formally implemented in the study protocol after subject recruitment and data collection had already begun. Therefore this study only reports data from the portion of enrolled participants who completed the FFMQ at baseline.
The Five Facet Mindfulness Questionnaire (FFMQ) is a self-report survey measuring total mindfulness and five different facets of mindfulness. The FFMQ was derived from exploratory factor analysis of the combined item pool of five independently-developed mindfulness assessment tools. It consists of 39 five-point Likert scale (1=never or very rarely true to 5=very often or always true) questions, where higher scores reflect higher mindfulness. Total mindfulness scores range from 39-195, and total facet scores from 7-40. The FFMQ has been validated in both meditating and non-meditating samples, and was the highest rated mindfulness patient-report assessment tool for construct validity and internal consistency.21
Five individual facets of mindfulness
1) The Observing facet (8-item, range 8-40) measures the ability to attend to or notice internal and external stimuli, such as sensations, emotions, cognitions, sights, sounds, and smells.2, 33 2) The Describing facet (8-item, range 8-40) measures noting or mentally labeling observed stimuli with words.33, 34 3) The Acting-with-Awareness facet (8-item, range 8-40) measures attending to one's current actions, as opposed to behaving automatically or absentmindedly. 4) The Non-judging of experience facet (8-item, range 8-40) measures refraining from evaluation of one's sensations, cognitions, and emotions as negative, unacceptable, or intolerable.2, 33, 34 5) The Non-reactivity to experience facet (7-item, range 7-35) measures the ability to allow thoughts and feelings to come and go, without getting caught up in or carried away by them.
The WOMAC is a self-report questionnaire consisting of 3 subscales used to assess pain, stiffness, and physical function in patients with hip or knee osteoarthritis.35 The pain subscale consists of 5 items asking about pain during rest or activity, and can score from 0-500. The physical function subscale consists of 17 items asking about ability to perform daily activities, and can score from 0-1700.
The Six-minute Walk Test (6MW) is a measure of functional exercise capacity.36 Participants are asked to walk as far as possible within a six-minute period, and the distance covered at the end is noted and recorded.
Quality of life was assessed using the Short Form-36 (SF-36), a generic measure of health status with well-documented psychometric properties.37 The SF-36 consists of 36 questions related to eight dimensions of quality of life. The questions are transformed into a point scale ranging from 0 to 100, with higher scores indicating better perceived health status. Scores were combined to obtain two aggregate scores: the Physical Component Summary (PCS) score and the Mental Component Summary (MCS) score.
Beck Depression Inventory, second edition, (BDI) is a 21-question, validated, self-report instrument that measures the severity of depressive symptoms.38 Total scores range from 0-63, and higher scores reflect greater depressive symptoms. BDI scores ranging from 0-13 represent minimal depressive symptoms; scores from 14-19 are mild; scores from 20-28 are moderate; and scores from 29-63 represent severe depressive symptoms.
The Perceived Stress Scale (PSS) is a widely-used instrument for measuring the level of experienced stress, defined as the degree to which situations in one's life over the past month are appraised as unpredictable, uncontrollable, and overwhelming.39 It consists of 10 items, and higher scores reflect a greater degree of perceived stress.
Self-efficacy is the belief that one can successfully take action to produce a desired outcome, and was assessed using the Arthritis Self-Efficacy Scale-8 (ASES-8).40 The ASES-8 is a modified version of the Arthritis Self-Efficacy Scale that has been validated for patients with chronic pain. The patients rated each belief on a 10-point Likert scale, where 1 = very uncertain and 10 = very certain, to indicate the level of certainty that patients can perform a task; higher scores indicate higher self-efficacy. The total score was derived by taking the average of all responses.
Statistical analysis
All data were first examined visually and statistically for normality of distribution and values are presented as means ± standard deviation (SD) unless otherwise stated. Pearson's correlation coefficients were calculated to determine association between FFMQ and physical and psychological outcomes. A priori, we identified a list of commonly-used, confounding variables from previous studies of mindfulness in chronic pain populations, and we also considered plausible confounding factors that could conceptually or biologically affect both the independent (mindfulness) and dependent (health outcomes) variables. The potential confounding variables we selected were age, sex, race, educational background, body mass index (BMI), Kellgren-Lawrence (K/L) grade, and Community Healthy Activities Model Program for Seniors (CHAMPS) activity level, and were used in all multivariable models. Six separate models were conducted to determine the influence of each of the mindfulness measures (total and facet) on the measures of physical and psychological health. Finally, multiple regression models were used to test the hypothesized moderating effects of mindfulness (moderator) on the relation between pain (predictor) and psychological health (dependent variable). Interaction models were run for all FFMQ facets and all psychological outcomes. We calculated high, medium, and low variable levels as one SD above the mean, within 1 SD of the mean, and below 1 SD of the mean respectively. Model assumptions and appropriateness were examined both graphically and analytically using scatterplots, studentized residuals, and Cook's distance test. Data were analyzed using SAS statistical software (Version 9.4). ModGraph-I was used to create the moderation plot.41 A p value of 0.05 or less was considered statistically significant.
Results
Demographic and clinical characteristics
Table 1 summarizes demographic and clinical participant characteristics. The analysis included data obtained from 80 participants who had a mean age of 60 years and an average BMI of 33 kg/m2, were predominantly female (76%), white (50%), and college graduates (50%). The mean WOMAC pain and function scores were respectively 259 and 916 and similar to those from previous knee OA studies. The mean BDI score was 8.0, which represents minimal depressive symptoms.38
Table 1. Baseline Characteristics and Health Outcomes (n = 80).
| Variables | Mean ± SD |
|---|---|
| Age, yrs. | 60.3 ± 10.3 |
| BMI, kg/m2 | 33.0 ± 7.1 |
| Sex, n (%) | |
| Male | 19 (23.2) |
| Female | 61 (76.3) |
| Race, n (%) | |
| White | 40 (50.0) |
| Black or African American | 25 (31.3) |
| Other/unknown | 15 (18.2) |
| Education, n (%) | |
| High school or less | 11 (13.8) |
| Some college/Trade school | 29 (36.2) |
| College grad | 18 (22.5) |
| Graduate school | 22 (27.5) |
| K/L grade, n (%)+ | |
| 0-2 | 37 (47.4) |
| 3-4 | 41 (52.6) |
| CHAMPS Activity: (moderate-high intensity, calories/week) | 1458.1 ± 1882.0 |
| WOMAC pain subscale (Range: 0-500) | 259.3 ± 98.8 |
| WOMAC function subscale (Range: 0-1700) | 916.0 ± 362.4 |
| Six-Minute Walk Test (Range: 400-700#*) | 403.2 ± 90.2 |
| SF-36 physical component score (Range: 0-100#) | 36.3 ± 9.1 |
| SF-36 mental component score (Range: 0-100#) | 53.2 ± 8.7 |
| Arthritis Self-Efficacy Scale (Range: 0-10#) | -86.3 ± 2.0 |
| Beck Depression Inventory (Range: 0-63) | 7.5 ± 8.5 |
| Perceived Stress Scale (Range: 0-40) | 12.8 ± 6.7 |
K/L grade for 2 participants not recorded
Higher score indicates improved health
Normal range reported for the general population36
Values reported as mean ± SD unless otherwise noted
Table 2 provides the descriptive statistics for each item in the Five Facet Mindfulness Questionnaire. The mean for total mindfulness was 142.8 with a standard deviation of 16.6. The Non-reacting facet had the lowest mean score of 22.9, whereas the other four facets had similar mean scores. Mindfulness facet score distributions showed modest variability with standard deviations ranging from 4.7 to 6.6.
Table 2. Baseline Mindfulness Scores.
| Variables | Mean ± SD | Score Range |
|---|---|---|
| FFMQ-Total | 142.8± 16.6 | 39-195 |
| FFMQ- Observing | 28.7 ± 6.1 | 8-40 |
| FFMQ- Describing | 31.1 ± 5.6 | 8-40 |
| FFMQ- Acting with Awareness | 30.2 ± 6.6 | 8-40 |
| FFMQ- Non-judging | 29.9 ± 5.9 | 8-40 |
| FFMQ- Non-reacting | 22.9 ± 4.7 | 7-35 |
FFMQ- Five Facet Mindfulness Questionnaire
Associations between FFMQ total and facet scores and health outcomes
Table 3 illustrates the associations between the FFMQ (total and facet scores) and health outcome measures. All significant associations were in the anticipated direction; that is, higher mindfulness was associated with higher quality of life, and lower depressive symptoms and stress. The correlation analyses revealed a pattern in which mindfulness was predominantly associated with outcomes of psychological health more so than with outcomes of pain or physical health. Higher total mindfulness score was associated with higher self-efficacy (r = 0.28, 95% Confidence Interval (CI) = 0.06 to 0.47) and greater mental and physical component quality of life (SF-36 MCS: r = 0.45, 95% CI = 0.25 to 0.61; SF-36 PCS: r = 0.23, 95% CI = 0.01 to 0.43). Higher total mindfulness was associated with lower depressive symptoms (r = -0.47, 95% CI = -0.62 to -0.27) and lower stress (r = -0.51, 95% CI = -0.65 to -0.32). Mindfulness was not significantly correlated with pain, physical functioning, or mobility.
Table 3. Correlation Coefficients between Mindfulness and Health Outcomes.
| Mindfulness | Physical Outcomes r (P-value) | Psychological Outcomes r (P-value) | ||||||
|---|---|---|---|---|---|---|---|---|
|
| ||||||||
| FFMQ Score (Score Range) | WOMAC Pain (0-500) | WOMAC Physical Function (0-1700) | 6MW (400-700)*# | SF-36 PCS (0-100) * | SF-36 MCS (0-100) * | BDI-II (0-63) | ASES-8 (0-10)* | PSS (0-40) |
| Total (39-195) | -0.12 (0.30) | -0.04 (0.75) | 0.05 (0.69) | 0.23 (0.04) | 0.45 (<0.001) | -0.47 (<0.001) | 0.28 (0.01) | -0.51 (<0.001) |
| 95% CI† | [-0.33, 0.11] | [-0.25, 0.19] | [-0.18, 0.27] | [0.01, 0.43] | [0.25, 0.61] | [-0.62, -0.27] | [0.06, 0.47] | [-0.65, -0.32] |
| Observing (8-40) | -0.12 (0.28) | -0.06 (0.61) | 0.01 (0.91) | 0.08 (0.46) | -0.10 (0.39) | -0.06 (0.61) | 0.09 (0.41) | 0.08 (0.48) |
| 95% CI | [-0.33, 0.10] | [-0.27, 0.16] | [-0.21, 0.24] | [-0.14, 0.30] | [-0.31, 0.13] | [-0.28, 0.17] | [-0.13, 0.31] | [-0.14, 0.29] |
| Describing (8-40) | -0.09 (0.43) | 0.02 (0.86) | 0.12 (0.30) | 0.22 (0.05) | 0.44 (<0.001) | -0.37 (<0.001) | 0.26 (0.02) | -0.55 (<0.001) |
| 95% CI | [-0.30, 0.13] | [-0.20, 0.24] | [-0.11, 0.33] | [0.00, 0.42] | [0.24, 0.60] | [-0.55, -0.16] | [0.04, 0.45] | [-0.69, -0.38] |
| Acting with Awareness (8-40) | 0.03 (0.79) | 0.10 (0.39) | -0.11 (0.33) | 0.10 (0.40) | 0.37 (<0.001) | -0.31 (0.005) | 0.20 (0.07) | -0.40 (<0.001) |
| 95% CI | [-0.19, 0.25] | [-0.13, 0.31] | [-0.33, 0.11] | [-0.13, 0.41] | [0.16, 0.54] | [-0.50, -0.10] | [-0.02, 0.40] | [-0.57, -0.20] |
| Non-judging (8-40) | -0.01(0.93) | -0.02 (0.87) | 0.09 (0.46) | 0.08 (0.47) | 0.46 (<0.001) | -0.36 (0.001) | 0.05 (0.69) | -0.41 (<0.001) |
| 95% CI | [-0.23, 0.21] | [-0.24, 0.20] | [-0.14, 0.30] | [-0.14, 0.30] | [0.26, 0.61] | [-0.54, -0.15] | [-0.18, 0.26] | [-0.58, -0.21] |
| Non-reacting (7-35) | -0.18 (0.11) | -0.19 (0.09) | 0.06 (0.61) | 0.21 (0.06) | 0.10 (0.39) | -0.24 (0.03) | 0.20 (0.08) | -0.16 (0.15) |
| 95% CI | [-0.38, 0.04] | [-0.39, 0.03] | [-0.17, 0.28] | [-0.01, 0.43] | [-0.12, 0.31] | [-0.44, -0.02] | [-0.02, 0.40] | [-0.37, 0.06] |
Higher scores indicate improved health.
Normal range reported for the general population36.
CI = Confidence Interval
Of the five facets, the Describing facet was significantly associated with five outcome measures (SF-36 MCS, PCS, BDI, ASES, and PSS), and both the Acting-with-Awareness and Non-judging facets were significantly associated with 3 outcome measures (SF-36 MCS, BDI, and PSS). These three facets were the facets found most frequently associated with psychological outcome measures. The Observing facet, however, did not have any significant associations with health outcomes in this population.
Table 4 summarizes the associations between mindfulness measures and health outcomes after controlling for confounding variables. The results revealed a similar pattern from the unadjusted correlation analyses wherein the total mindfulness score was associated with outcomes of psychological health more so than with measures of pain or physical health. Of note, the association between the Acting-with-Awareness facet and self-efficacy (beta =0.10, 95% CI= 0.01 to 0.18) was only evident on multivariable analysis. The association between the Non-reacting facet and depressive symptoms was only evident on the unadjusted correlation analysis.
Table 4. Multivariable Analyses of Health Outcomes and Mindfulness.
| Dependent Variable (Score Range) | Independent Variable FFMQ | Beta Coefficient | 95% Confidence Intervals | Standard error | P value | |
|---|---|---|---|---|---|---|
| WOMAC Pain (0-500) | Total Score | -6.26 | (-13.23, 0.70) | 3.49 | 0.08 | |
| Observing | -2.05 | (-5.70, 1.60) | 1.83 | 0.27 | ||
| Describing | -2.38 | (-6.47, 1.72) | 2.05 | 0.25 | ||
| Acting with Awareness | -1.51 | (-5.39, 2.37) | 1.94 | 0.44 | ||
| Non-judging | -1.06 | (-4.88, 2.76) | 1.91 | 0.58 | ||
| Non-reacting | -3.39 | (-8.03, 1.24) | 2.32 | 0.15 | ||
|
| ||||||
| WOMAC Physical Function (0-1700) | Total Score | -15.54 | (-41.82, 10.74) | 13.16 | 0.24 | |
| Observing | -1.25 | (-14.94, 12.45) | 6.86 | 0.86 | ||
| Describing | -1.33 | (-16.72, 14.06) | 7.71 | 0.86 | ||
| Acting with Awareness | -5.91 | (-20.33, 8.51) | 7.22 | 0.41 | ||
| Non-judging | -3.82 | (-18.05, 10.40) | 7.13 | 0.59 | ||
| Non-reacting | -15.64 | (-32.73, 1.44) | 8.56 | 0.07 | ||
|
| ||||||
| 6 Minute Walk (400-700)*# | Total Score | 3.31 | (-2.89, 9.50) | 3.10 | 0.29 | |
| Observing | -0.54 | (-3.61, 2.53) | 1.54 | 0.73 | ||
| Describing | 2.43 | (-1.04, 5.90) | 1.74 | 0.17 | ||
| Acting with Awareness | 1.69 | (-1.60, 4.97) | 1.64 | 0.31 | ||
| Non-judging | 1.14 | (-2.19, 4.48) | 1.67 | 0.50 | ||
| Non-reacting | 0.44 | (-3.49, 4.37) | 1.97 | 0.82 | ||
|
| ||||||
| SF-36 Physical Component Summary (0-100)* | Total Score | 0.69 | (0.06, 1.31) | 0.31 | 0.03 | |
| Observing | 0.06 | (-0.27, 0.39) | 0.17 | 0.72 | ||
| Describing | 0.42 | (0.06, 0.78) | 0.18 | 0.02 | ||
| Acting with Awareness | 0.28 | (-0.07, 0.63) | 0.17 | 0.11 | ||
| Non-judging | 0.05 | (-0.30, 0.40) | 0.17 | 0.78 | ||
| Non-reacting | 0.38 | (-0.04, 0.79) | 0.21 | 0.08 | ||
|
| ||||||
| SF-36 Mental Component Summary (0-100)* | Total Score | 1.31 | (0.68, 1.95) | 0.32 | <0.001 | |
| Observing | -0.22 | (-0.58, 0.14) | 0.18 | 0.23 | ||
| Describing | 0.73 | (0.36, 1.10) | 0.19 | <0.001 | ||
| Acting with Awareness | 0.75 | (0.41, 1.09) | 0.17 | <0.001 | ||
| Non-judging | 0.67 | (0.32, 1.01) | 0.17 | <0.001 | ||
| Non-reacting | 0.17 | (-0.30, 0.63) | 0.23 | 0.48 | ||
|
| ||||||
| Brief Depression Inventory (0-63) | Total Score | -1.15 | (-1.77, -0.54) | 0.31 | <0.001 | |
| Observing | 0.00 | (-0.34, 0.35) | 0.17 | 0.98 | ||
| Describing | -0.53 | (-0.91, -0.16) | 0.19 | 0.006 | ||
| Acting with Awareness | -0.48 | (-0.83, -0.13) | 0.18 | 0.009 | ||
| Non-judging | -0.52 | (-0.87, -0.18) | 0.17 | 0.004 | ||
| Non-reacting | -0.37 | (-0.81, 0.07) | 0.22 | 0.10 | ||
|
| ||||||
| Perceived Stress Scale (0-40) | Total Score | -1.07 | (-1.53, -0.60) | 0.23 | <0.001 | |
| Observing | 0.20 | (-0.07, 0.47) | 0.14 | 0.14 | ||
| Describing | -0.68 | (-0.94, -0.42) | 0.13 | <0.001 | ||
| Acting with Awareness | -0.62 | (-0.87, -0.37) | 0.12 | <0.001 | ||
| Non-judging | -0.46 | (-0.73, -0.20) | 0.13 | <0.001 | ||
| Non-reacting | -0.16 | (-0.51, 0.19) | 0.18 | 0.36 | ||
|
| ||||||
| Arthritis Self-Efficacy Scale (0-10)* | Total Score | 0.22 | (0.07, 0.37) | 0.08 | 0.005 | |
| Observing | 0.05 | (-0.04, 0.13) | 0.04 | 0.27 | ||
| Describing | 0.11 | (0.03, 0.20) | 0.04 | 0.01 | ||
| Acting with Awareness | 0.10 | (0.01, 0.18) | 0.04 | 0.03 | ||
| Non-judging | 0.02 | (-0.07, 0.11) | 0.04 | 0.65 | ||
| Non-reacting | 0.09 | (-0.01, 0.19) | 0.05 | 0.09 | ||
All models were adjusted for: age, sex, race, BMI, K/L grade, education, and physical activity.
Higher scores indicate improved health.
Normal range reported for the general population36
Moderation Effects
To illustrate the nature of this moderation effect, associations between high, medium, and low levels of the predictor (i.e. pain) and dependent outcome (i.e. stress) were tested at high, medium, and low levels of the moderator (i.e. mindfulness, Acting-with-Awareness [Figure 1]). This figure shows that mindfulness has a direct relationship with stress. All participants with low mindfulness have a higher level of stress, regardless of their level of pain. The differences in stress levels are greatest between high and low mindfulness at lower levels of pain; therefore as pain increases, the difference in stress decreases. The Acting-with-Awareness facet significantly moderated the relationship of WOMAC Pain on Perceived Stress (beta = 0.002, P = 0.02). No significant moderation was found with the other moderators (i.e. FFMQ- total, Describing, Non-judging, and Non-reacting) or dependent health outcomes (i.e. BDI, SF-36 PCS and MCS, and ASES-8) investigated.
Figure 1. Mindfulness (Acting-with-Awareness facet) Moderates the Influence of Pain on Stress.
As pain intensity increases, stress increased across the three levels of mindfulness, but stress remained highest across those with lower levels of mindfulness. This finding shows that mindfulness may help buffer from increased perceived stress from chronic pain.
Discussion
This is the first study to report that mindfulness is associated with relevant health outcomes among non-surgical participants with symptomatic knee OA. Overall, we found that mindfulness is directly associated with depression, stress, self-efficacy, and health-related quality of life in knee OA patients. Specifically, participants reporting higher mindfulness tended to have lower depressive symptoms and perceived stress, as well as higher self-efficacy and health-related quality of life. Contrary to our hypothesis, mindfulness is not directly associated with pain, but it does moderate the influence of pain on stress, which suggests that mindfulness may alter the way one copes with pain. Of the 5 mindfulness facets, 3 (Describing, Non-judging, and Acting-with-Awareness) were more frequently found to be associated with psychological health outcomes than others. In particular, the Acting-with-Awareness facet moderated the pain-stress relationship. Among participants with higher mindfulness, pain intensity had less of an impact on perceived stress. This suggests that although mindfulness may not alter the severity of pain, it may influence the psychosocial effects of chronic pain. The pattern of facet associations found in our study identifies unique elements of mindfulness that may be of particular importance in optimizing treatment for those with knee OA.
Our results extend the field of mind-body medicine research that found that mindfulness is associated with psychological outcomes in patients with chronic OA pain and gives credence to the conceptualization of OA as a complex, multi-factorial disease affecting the health of the entire body.42 Most strengths of association from our results were of similar magnitude with those reported in previous chronic pain studies,4, 33 which often included patients with fibromyalgia, low back pain, or a heterogeneous mixture of various chronic pain conditions. The similar patterns of association found from our study may indicate commonalities of pain processing that exist in different types of chronic pain diseases. Some of our study results, however, did differ from those of chronic pain samples previously reported. For example, two correlational studies found a significant direct association between mindfulness and pain intensity,33, 43 which was inconsistent with our study results. Because these studies included participants with a variety of chronic pain disease types, our disparate results may reflect how knee OA incorporates or expresses pain processing mechanisms in different ways.27 Despite these differences, we speculate that the consistent pattern of association between mindfulness and psychological outcomes in our study imply that knee OA patients may benefit from mind-body interventions.
Similar to the results of other studies, of the five facets the Acting-with-Awareness,44 Describing, and Non-judging facets showed the most significant associations with psychological outcomes for participants. One way that mindfulness may improve health is by improving the ability to be aware of the presence of pain, to be able to describe or mentally label observed stimuli with words, and react with less self-judgment, which can lead to positive pain coping habits.45, 46 However, the Observing facet was not directly associated with any of the outcomes investigated. This finding is consistent with previous research that found that the Observing subscale of the FFMQ may only be sensitive to changes in those who have experience in mindfulness training,33, 47 and therefore implies that its lack of association with health outcomes may reflect a psychometric flaw inherent in the FFMQ rather than a diminished role for Observation as a relevant component of the mindfulness construct. The differential associations found in our facet analyses support the assessment of mindfulness as a construct composed of related, but distinct facets. Further research is needed to improve and calibrate measurement tools to more accurately operationalize the facets of mindfulness. A greater understanding of how these facets relate with health outcomes may inform the optimization of mind-body interventions to amplify the positive effects that mindfulness may have in patients with chronic pain.
In addition to its direct association on stress, the Acting-with-Awareness facet had a moderation effect wherein higher mindfulness was associated with lower stress at each of the three levels of pain. The relationship between pain and stress was weaker for those with higher mindfulness. Across all three levels of mindfulness, pain intensity increased as stress increased, but stress remained highest among those with lower levels of mindfulness. This finding implies that acting with awareness, or being able to attend to one's current actions, may attenuate the influence that chronic pain often has on stress. Because mindfulness appears to produce its strongest buffering effect between pain and stress when pain levels are low, it is possible to infer that as pain intensifies, this buffering effect decreases. Results from moderation analysis fall in accordance with the theory that mindfulness changes the relationship between a person and their pain, and agree with a cross-sectional study that also found that mindfulness moderated the influence of pain on psychological stress in a sample of 201 rheumatoid arthritis patients.48 Importantly, we speculate from our results that the documented consistent benefits of mind body therapies for chronic pain patients may partially result from improved mindfulness49, 50 Our moderation results underscore the importance of understanding how treatments affect the interaction of chronic pain with psychosocial health. By reducing the impact of pain on psychosocial health or improving pain coping abilities, novel treatments may indirectly treat chronic pain patients without necessarily reducing actual levels of pain.
The limitations of our study included the use of a cross-sectional design through which we are unable to make definitive conclusions about causality between mindfulness and parameters of health. In addition, our study sample was not an epidemiological representative of all chronic pain or knee OA patients, which limits generalizability. Because this study was a secondary analyses of data which were not collected with the primary purpose of addressing our investigative questions, our results should be confirmed in studies explicitly designed to evaluate the associations between mindfulness and health outcomes in knee OA patients. Another limitation may be that our usage of multiple comparisons, without adjusting the cutoff point for statistical significance, may have yielded false discoveries (Type I error). Despite these limitations, our representative sample included knee OA patients who are routinely seen in the clinical setting. In addition, based on the strong degree of significance in the associations found in our results, the potential limitation of calculating false statistical discoveries would not have changed our primary result: that mindfulness was predominantly associated with psychological outcomes in our knee OA patient population.
In conclusion, the results of this first study support the associations between mindfulness levels and psychological health outcomes for knee OA patients. The Describing, Acting-with-Awareness, and Non-judging facets may be the most contributory elements of mindfulness toward affecting health outcomes, which may inform how mind-body interventions could enhance their health benefits in knee OA patients. Importantly, the moderation effect of mindfulness implies a valuable role for improving pain coping skills, and further study is needed to identify which pain coping skills are most relevant, how they are affected by intervention, and how they should be incorporated in treatment.
Acknowledgments
The authors gratefully acknowledge fellow members of the Center for Complementary and Integrative Medicine: Dr. Jeffrey Driban, Dr. Jolanta Marszalek, Emily Wolcott, Sun Yu, and Shivani Bigler for their helpful comments on the manuscript and assistance in organizing the literature review.
Supported by: National Center for Complementary and Integrative Health (R01AT005521 and K24AT007323), and National Center for Advancing Translational Sciences (UL1TR001064) at the National Institutes of Health.
Role of the funding source: This study is supported by the National Institutes of Health (R01AT005521, K24AT007323, and UL1TR001064). The contents of this manuscript are solely the responsibility of the authors and do not necessarily represent the official views of the National Institutes of Health. The investigators are solely responsible for the content of the manuscript and the decision to submit for publication. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Footnotes
Author contributions: All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Lee had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study conception and design: Lee, Price, Harvey, Morgan L, Morgan N, Wang
Acquisition of data: Lee, Price, Harvey, Morgan L, Morgan N, Wang
Analysis and interpretation of data: Lee, Price, Harvey, Morgan L, Morgan N, Wang
Conflict of Interests: The authors declare that they have no conflict of interest.
Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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