Psychometric Properties of the Knee Osteoarthritis Pain Index.

Objectives: The current study sought to evaluate the psychometric properties of a newly developed Knee OsteoArthritis Pain Index (KOAPI), derived from the Brief Pain Inventory (BPI), among individuals with knee osteoarthritis (KOA).

Methods: This study consisted of secondary data analysis of two clinical trials. In study 1, 241 individuals with KOA were evaluated before total knee arthroplasty and six months post-surgery. In study 2, 37 individuals with KOA participated in a randomized, double-blind, placebo controlled, two-way crossover study in which they received either a COX-2 inhibitor followed by a placebo or a placebo followed by a COX-2 inhibitor. The KOAPI was derived from the BPI and included three BPI pain severity items (worst, average, current) and the BPI pain interference item related to pain when walking.

Results: The KOAPI showed excellent model fit (CFI = 0.99; TFI: 0.98-0.99; RMSEA: 0.08-0.001), good reliability (Cronbach's alpha: 0.84-0.87) and high convergent validity with the Western Ontario and McMaster Universities Osteoarthritis Index (r = 0.66; 95% CI: 0.44, 0.81) and the Pain Catastrophizing Scale (r = 0.50; 95% CI: 0.39, 0.60).

Conclusions: Overall, the psychometric properties of the KOAPI were comparable or better than those produced by the original BPI pain severity subscale. The KOAPI may be a helpful screening and outcome measure for individuals with KOA that more closely captures symptoms which drive patients to seek clinical care.