Collins JE, Neogi T, Losina E, et al. - Since knee osteoarthritis (OA) is a heterogeneous disease, with most patients experiencing slow disease progression and some experiencing rapid deterioration, researchers sought to identify subsets of patients with symptomatic knee OA who were experiencing rapid structural progression. They chose candidates from the Osteoarthritis Initiative with baseline Kellgren/Lawrence (K/L) grades 1–3 and knee pain, as well as joint space width on fixed-flexion knee radiographs assessed at baseline and with ≥ 1 follow-up over 8 years. Data from 1,578 candidates were used in this analysis. Prior knee surgery was linked to being on the late-progressing vs stable trajectory, whereas obesity was linked to being on the early-progressing vs stable trajectory. In addition to identifying a subset of individuals experiencing early structural progression, 8-year longitudinal data enabled the identification of a late-progressing trajectory. It was critical to include information about knee replacement in order to correctly identify longitudinal structural trajectories in knee OA.