Objectives: Pain catastrophizing impacts symptoms and outcomes for knee osteoarthritis (OA). We evaluated the internal consistency, content, construct and structure validity of the Pain Catastrophizing Scale (PCS) in patients with knee OA.
Methods: We evaluated content validity of PCS via cognitive interviews. We then recruited patients with knee OA enlisted for knee replacement (KR) surgery in a Singapore tertiary referral hospital for cross-sectional validation evaluation of PCS. Data was collected 2 weeks prior to KR. Analyses was guided by the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) framework for internal consistency, construct validity and structure validity.
Results: Adequate content validity was confirmed from 10 patients in cognitive interviews. 675 (70.4% female, mean (standard deviation, SD) age = 65.52 (6.84) years) were included (91.7% total KR, 8.3% unicompartmental KR) in the cross-sectional study. The mean (SD) PCS score was 12.65 (10.55), with 0.14% and 8.63% ceiling and floor effects, respectively. PCS demonstrates high internal consistency (Cronbach's alpha = 0.94). Construct validity was demonstrated by fulfilment of seven out of seven (100%) a priori hypotheses. PCS was strongly correlated with anxiety and depression, and moderately correlated with physical functioning and mental health domains of the short form 36 health survey (SF-36). Sensitivity analyses between Chinese and non-Chinese subgroups are generally consistent. From confirmatory factor analysis, the PCS model showed good fit for a second-order, three-factor structure (CFI = 0.965, TLI = 0.950, SRMR = 0.031).
Conclusions: This study supports internal consistency, construct validity and structural validity of PCS as a measure of pain catastrophizing in knee OA patients. Key points • The PCS is validated for measuring pain catastrophizing in knee OA patients, for evaluation of possible link to post-KR surgery satisfaction outcomes and other purposes.
Keywords: Knee osteoarthritis; Pain catastrophizing.