Intermittent and constant pain and physical function or performance in men and women with knee osteoarthritis: data from the osteoarthritis initiative.

Severe constant and intermittent knee pain are associated with "unacceptable" symptoms in older adults with osteoarthritis (OA) [22]. We hypothesized that constant and intermittent pain would be independently related to physical function, with intermittent knee pain being a better predictor of future declines in physical function in early symptomatic knee OA. This study included men (n = 189) and women (n = 133) with radiographic, unilateral knee OA, observed using data from the Osteoarthritis Initiative (OAI). Pain types were measured using the Intermittent and Constant Osteoarthritis Pain (ICOAP) scale. Physical function was measured using the Western Ontario and McMaster Universities Arthritis Index (WOMAC-PF) and Knee Injury and Osteoarthritis Outcome Score (KOOS-FSR) and physical performance tests. High baseline intermittent (B = 0.277; p = 0.001) and constant (B = 0.252; p = 0.001) knee pain were related to poor WOMAC-PF. Increased constant (B = 0.484; p = 0.001) and intermittent (B = 0.104; p = 0.040) pain were related to 2-year decreased WOMAC-PF. High baseline intermittent knee pain predicted poor KOOS-FSR at year 2 (B = -0.357; p = 0.016). Increased constant pain was related to decreased chair stand test performance over 2 years in women (B = 0.077; p = 0.001). High baseline intermittent pain was related to poor performance on repeated chair stands (B = 0.035; p = 0.021), while baseline constant pain was related to poor 400-m walk performance in women (B = 0.636; p = 0.047). Intermittent and constant knee pain were independent factors in self-perceived physical function and were important predictors of future limitations in physical function. Identifying intermittent and constant pain in early symptomatic OA may allow patients to adopt strategies to prevent worsening pain and future declines in physical function.