Background/Purpose:   Few strategies to improve pain outcome in knee OA exist, in part because methods to evaluate this outcome are not established.  ICOAP development included formulation of pain experience stages (Hawker 2008): 1) predictable pain, known trigger, only limiting high impact activity; 2) mixed predictable/unpredictable pain, more constant, affecting some daily activities; 3) pain constant, superimposed unpredictable, major activity avoidance.  We hypothesized that the probability of a good pain experience outcome is associated inversely with baseline depression and pain catastrophizing and directly with self-efficacy and social support.

Methods:   Study participants (all with knee OA) reported pain stage (no pain, or stages 1, 2, or 3) at baseline and 2 years.  1-month test-retest reliability was excellent (weighted κ = 0.85; n = 28).  Baseline assessments utilized the Geriatric Depression Scale, Pain Catastrophizing Scale, function Arthritis Self-Efficacy Scale, and MOS Social Support Survey.  Good outcome was defined: baseline → 2-year reports of (no pain or stage 1) → (no pain or stage 1) or (stage 2 or 3) → (no pain or stage 1).  Poor outcome was: (stage 2 or 3) → (stage 2 or 3) or (no pain or stage 1) → (stage 2 or 3).  In multivariable logistic regression, pain outcome was the dependent variable, and all baseline variables with univariate p ≤ 0.20 potential predictors.

Results:  212 persons [163 (77%) women, mean age 65 (10, SD), BMI 28.5 (5.7)] comprised the sample. 136 (64%) had a good pain outcome and 76 (36%) a poor outcome.  Several baseline factors were associated with good pain outcome in univariate analyses (Table 1).  In multivariable analysis, higher self-efficacy was associated with a significantly higher likelihood of good outcome; higher pain catastrophizing and BMI were associated with a lower likelihood of good outcome (Table 2).

Conclusion:   The odds of a good 2-year pain experience outcome in knee OA were lower in persons with greater pain catastrophizing and/or higher BMI, and higher in persons with greater self-efficacy.  Specifically targeting these factors may help improve pain outcome in knee OA.

Table 1.  Baseline Characteristics of Good and Poor 2-Year Pain Experience Outcome Groups

*Value shown is mean (SD) unless otherwise indicated

**p value for depressive symptoms as a continuous variable also exceeded 0.20

***Comorbidity questionnaire modification of Charlson Index (continuous)

Table 2.  Multivariable Logistic Regression Model: Associations between Baseline Covariables and Baseline-to-2-Year Good Pain Experience Outcome (Dependent Variable) 

Findings are adjusted for all other variables in the table.