Trajectories of Structural Disease Progression in Knee Osteoarthritis.

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 patients with symptomatic knee OA experiencing rapid structural progression.
METHODS: We selected participants from the Osteoarthritis Initiative with baseline Kellgren/Lawrence (K/L) grades 1-3 and knee pain, and with joint space width (JSW) on fixed-flexion knee radiographs assessed at baseline and with ≥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 baseline characteristics and the JSW trajectory group.
RESULTS: We used data from 1,578 participants. Baseline radiographic severity was K/L grade 1 in 17%, K/L grade 2 in 50%, and K/L grade 3 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 reclassified to 1 of the progressing trajectories. Prior knee surgery was associated with being in the late-progressing versus the stable trajectory, while obesity was associated with being in the early-progressing versus 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.