Activity Limitations in Patients with Axial Spondyloarthritis: A Role for Fear of Movement and (Re)injury Beliefs.

OBJECTIVE: To determine whether fear of movement and (re)injury [FOM/(R)I] beliefs, measured with the Tampa Scale for Kinesiophobia 11-item version (TSK-11), influence activity limitations and mediate the relationship between pain severity and activity limitations in axial spondyloarthritis (axSpA).

METHODS: In 173 patients with axSpA, these data were collected: sex, body mass index, disease duration, medication, activity limitations (BASFI; Bath Ankylosing Spondylitis Functional Index), disease activity [Bath Ankylosing Spondylitis Disease Activity Index (BASDAI); BASDAIinf, items 5 and 6; BASDAIpain, items 2 and 3; C-reactive protein and physician's global assessment], spinal mobility (BASMI; Bath Ankylosing Spondylitis Metrology Index), and FOM/(R)I (TSK-11). Scaling assumptions and reliability of TSK-11 were tested with item-to-total correlations, item variances, and Cronbach's alpha coefficient. Hypothesis testing determined TSK-11's construct validity. Multiple linear regression showed the contribution of TSK-11 to BASFI (enter and backward modeling). Mediation by TSK-11 was analyzed (bias-corrected bootstrapping and Sobel test).

RESULTS: Adequate scale (Cronbach's alpha = 0.80) and item internal consistency (range item-scale correlations 0.41-0.58, except for item 5, r = 0.23), equal item-scale correlations, and item variances were found for TSK-11. Construct validity was confirmed, except for the hypothesized positive relationship between TSK-11 and BASMI. Regression models (enter method, adjusted R2 range 53-74%) consistently identified TSK-11 as a determinant of BASFI (β range 0.155 to 0.321, p < 0.05), although BASMI (β range 0.441 to 0.537) and disease activity (β range 0.243 to 0.571, p < 0.05) were the largest determinants. TSK-11 partially mediated the BASDAIpain/BASFI relationship (B = 0.107; Sobel test, p = 0.004; bias-corrected CI 0.046-0.197).

CONCLUSION: TSK-11 is a promising and valid tool to assess fearful beliefs in relation to activity limitations in axSpA. Future research applying TSK-11 may reveal FOM/(R)I as a novel treatment target in axSpA.