Natural course of knee osteoarthritis in middle-aged subjects with knee pain: 12-year follow-up using clinical and radiographic criteria

Objective: To explore the natural course of knee osteoarthritis (OA) in a middle-aged population with chronic knee pain. Methods: A population-based sample of 143 subjects (mean age 45 (range 35-54), 44% women) with knee pain (>3 months) at inclusion was studied. Weightbearing posteroanterior tibiofemoral (TF) radiographs were obtained at baseline and 12 years later, and classified according to Kellgren/Lawrence (K/L). Patellofemoral (PF) OA was determined at 5-and 12-years' follow-up using a skyline view and a cut-off point of <5 mm joint space width. The ACR clinical criteria were used at baseline. Results: Seventy-six (53%) had no TF OA (K/L 0) at baseline, but 49 had clinical OA. Overall, 65/76 (86%) developed incident TF OA over 12 years (K/L >= 1): 44/49 (90%) of the subjects with clinical OA and 21/27 (78%) without clinical OA. Progression was found in 65/67 (97%) with TF OA at baseline. Of the 84 with no PF OA at the 5-year examination, 26 (31%) developed PF OA over 7 years. Conclusion: A majority of the subjects with chronic knee pain developed knee OA over 12 years. It is concluded that knee pain is often the first sign of knee OA.