Fear of movement, obesity and physical activity in knee osteoarthritis

Background Fear of movement is common in knee osteoarthritis but its role in reducing physical activity, and how it interacts with pain, remain unclear. The purpose of this study was to investigate how fear of movement affects the relationships between daily step count with each of pain intensity and pain sensitivity in symptomatic knee osteoarthritis. Methods Thirty-one participants with symptomatic knee osteoarthritis were included (17 female, 14 male, 0 intersex; age 65.3 [7.0] years, body mass index (BMI) 30.0 [5.0] kg/m^2). Mean daily step count was captured using a commercial 3-axis accelerometer over 7 days. Pain intensity was measured with the pain subscale of the Knee Injury and Osteoarthritis Outcome Score. Pain sensitivity was measured with pressure pain threshold. Fear of movement was self-reported on the Brief Fear of Movement Scale. After adjusting for covariates (age, BMI), regressions tested the associations between step count and pain intensity without, then with, fear of movement and its interactions. The analysis was repeated using pain sensitivity. Findings Step count was not significantly associated with pain intensity (R2 = 0.199, p = 0.107) nor with pain sensitivity (R2 = 0.217, p = 0.091). After adding fear of movement and its interactions to the model, the BMI x fear of movement interaction (p = 0.003) explained variance in step count (R2 = 0.512, p = 0.011). Those with greater fear of movement and larger BMI completed fewer steps compared to their peers. Interpretation Managing fear of movement may enhance rehabilitation to promote physical activity in knee osteoarthritis.