Understanding the Importance of Fear of Movement on Physical Activity and Physical Function in People with Knee Osteoarthritis

Abstract

Pain is the main reason why people with knee osteoarthritis (KOA) consult a healthcare provider (Jackson et al., 2020). The benefits of physical activity (PA) for KOA symptoms, including pain, are clear (Verhagen et al., 2019). However, people with KOA face numerous barriers to exercise. For example, fear of movement (FOM) is highly prevalent in KOA (58% to 86%) (Aykut Selçuk & Karakorum, 2020; Gunn et al., 2017; Tan et al., 2022) and is associated with lower levels of PA. It is likely that FOM affects the relationships between pain intensity and PA, but it is currently unclear if FOM is a covariate, a mediator, or a moderator in this relationship. The purpose of this study was to investigate how FOM affects the relationship between pain intensity or pain sensitization with the weekly level of PA in a sample of KOA. Additionally, this study investigated how FOM affects the relationships between pain intensity, physical function, and muscle impairments (including walking speed and quadriceps muscle power) in a sample of KOA. Participants who met the clinical criteria for KOA set forth by the American College of Rheumatology were included. PA was measured using a commercial 3-axis accelerometer (wGT3X-BT, Actigraph, USA). Pain intensity was measured via a validated, self-report questionnaire, the pain subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS-Pain). Pressure-pain threshold was determined using an algometer (FPX 25, Wagner, USA). FOM was self-reported by participants on the Brief Fear of Movement Scale (BFMS). Walking speed was measured from the 6-minute walk test. Quadriceps muscle power was obtained with a commercial dynamometer (System 4, Biodex, USA). Multiple linear regression was used to test the relationships between PA and pain (pain intensity and pain sensitization in separate analyses), after adjusting for age and body mass index (BMI). Then, the regression model was repeated, adding FOM and its interactions with the covariates. Thirty-one participants completed this study. After adjusting for the covariates (age and BMI), pain was not associated with PA levels (pain intensity: R2 = 0.199, p = 0.107; pain sensitization: R2 = 0.233, p = 0.072). After adding the moderator variable FOM and its interactions, our results showed a significant moderation effect of the BMI x FOM interaction (pain intensity: p = 0.003; pain sensitization: p = 0.002) in explaining variance in PA. The covariates, pain, and FOM (moderator) explained variance in PA in people with KOA (pain intensity: R2 = 0.525, p = 0.009; pain sensitization: R2 = 0.567, p = 0.005). FOM did not significantly moderate the relationship between pain intensity with either walking speed nor quadriceps muscle power (p > 0.05). Our results have important clinical implications. Our results suggest that those with higher levels of FOM combined with higher levels of BMI are less physically active compared to their counterparts. Rehabilitation clinicians should provide education on the benefits of PA and exercise in all people with KOA, but especially to those with higher BMI and higher FOM levels. Additionally, clinicians should use simple self-report tools such as the BFMS to screen for the level of FOM and provide additional education on safety of PA in KOA.