Objective: Knee osteoarthritis (OA) is a heterogeneous disease, with most patients experiencing slow disease progression and some with rapid deterioration. We aimed to identify groups of persons with symptomatic knee OA experiencing rapid structural progression.
Methods: We selected participants from the Osteoarthritis Initiative with baseline (BL) Kellgren-Lawrence (KL) grade 1 – 3, knee pain, and with joint space width (JSW) on fixed-flexion knee radiographs assessed at BL and ≥1 follow-up over 8 years. We used latent class growth analysis to identify subgroups of JSW progression, jointly modeling time to knee replacement (KR) to account for potential informative dropouts. After identifying trajectories, we used logistic regression to assess the association between BL characteristics and JSW trajectory group.
Results: We used data from 1578 participants. BL radiographic severity was KL1 in 17%, KL2 in 50%, and KL3 in 33%. We identified 3 distinct JSW trajectories: 86% stable, 6% with stable JSW followed by late progression, and 8% with early progression; incorporating information about KR resulted in 47% of KRs initially classified as stable being re-classified to one of the progressing trajectories. Prior knee surgery was associated with being in the late progressing vs. the stable trajectory while obesity was associated with being in the early progression vs. stable trajectory.
Conclusion: In addition to a subgroup of individuals experiencing early structural progression, 8-year longitudinal data allowed the identification of a late progressing trajectory. Incorporating information about KR was important to properly identify longitudinal structural trajectories in knee OA.