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 individuals (mean age 45 (range 35-54), 44% women) with knee pain (> 3 months) at inclusion was studied. Weight-bearing postero-anterior 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 year follow-up using a skyline view and a cut-off 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, whereof 49 had clinical OA. Overall, 65/76 (86%) developed incident TF OA over 12 years (K/L ≥1); 44/49 (90%) of the individuals 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 individuals with chronic knee pain developed knee OA over 12 years. We conclude that knee pain is often the first sign of knee OA.