Composite measures of physical activity and pain associate better with functional assessments than pain alone in knee...

Recent research showed that physical activity (PA)-adjusted pain measures were more strongly associated with radiographic osteoarthritis (OA) severity than an unadjusted pain measure. This exploratory study examined whether PA-adjusted pain measures were more closely associated with other key OA-related measures, compared to unadjusted pain scores.

Participants were 122 Veterans (mean age = 61.2 years, 88.5% male) with knee OA. Baseline Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain scores were adjusted for accelerometer-derived daily: (1) step counts, (2) minutes of any activity, (3) minutes of moderate or greater intensity activity, (4) minutes of light intensity activity, and (5) energy expenditure. Partial correlations, adjusted for age, sex, and body mass index, estimated associations of unadjusted and PA-adjusted WOMAC pain scores with functional assessments (6-minute walk test, 8-foot walk test, chair stand test, satisfaction with physical function), fatigue (Brief Fatigue Inventory), and anxiety/depressive symptoms (single item).

Significant (p < 0.05) associations were found in 29 of 36 of models. For the four function-related assessments, step count and energy expenditure-adjusted WOMAC pain scores had stronger associations (partial rs = 0.24-0.48) than WOMAC pain score (partial rs = 0.19-0.25). For fatigue and anxiety/depressive symptoms, WOMAC pain score had stronger, positive associations than most PA-adjusted pain scores. Of the PA-adjusted measures, the strongest associations overall were observed for step count and energy expenditure.

PA-adjusted pain scores may have particular value for OA studies involving functional assessments, whereas unadjusted WOMAC pain scores are more closely associated with psychological symptoms. This has implications for measurement in clinical OA studies.

NCT01058304 KEY POINTS: • Among patents with osteoarthritis, physical activity-adjusted pain measures (particularly those adjusted for step count and energy expenditure) were more strongly associated with measures of physical function, compared to unadjusted pain scores, whereas unadjusted pain score was more strongly associated with a measure of psychological symptoms. • In clinical osteoarthritis research, the most appropriate or sensitive symptom measure (pain vs. physical activity-adjusted pain) may depend on the type of intervention or outcome being studied.