Comment on paper by Collins and colleagues - Trajectories of Structural Disease Progression in Knee Osteoarthritis.

We read with interest the recently published paper by Collins and colleagues (1), which examined trajectories of worsening medial knee compartment joint space width (JSW). Osteoarthritis initiative (OAI) data from baseline to eight years of follow-up were used to define three JSW trajectories of persons with prevalent symptomatic knee OA, based on the presence of baseline pain and Kellgren and Lawrence OA grades of 1 to 3. Additionally, the investigators considered an analytic method that allowed for consideration of knee replacement participants, a subgroup whose knee OA data are usually censored in knee OA studies. Finally, the investigators determined trajectories of WOMAC Pain scores using the three trajectories defined from the JSW data as the predictor of WOMAC Pain scores over a nine-year period.