Current MRI-based definitions of knee osteoarthritis may be limited in predicting future radiographic disease, according to a study.

In a study of 1,621 Osteoarthritis Initiative participants without baseline radiographic tibiofemoral osteoarthritis, published in Arthritis & Rheumatology, investigators found that 17% of them met magnetic resonance imaging (MRI) osteoarthritis definition A (definite osteophyte + partial/full thickness cartilage loss or a single large osteophyte) and 24% of them met definition B (any cartilage loss + any osteophyte). Over 11 years, 41% of the knees with baseline MRI osteoarthritis by definition A developed incident radiographic osteoarthritis (Kellgren-Lawrence [KL] grade ≥ 2) compared with 18% of the knees not meeting the definition (adjusted risk ratio [RR] = 2.94, 95% CI = 2.34–3.68). For definition B, 36% of the knees positive at baseline developed KL grade ≥ 2 vs 17% of the knees negative at baseline (adjusted RR = 2.44, 95% CI = 1.97–3.03).

RRs were similar for outcomes of KL grade ≥ 2 plus joint space narrowing (3.01 for definition A, 2.34 for definition B) and KL grade ≥ 2 plus frequent knee symptoms (2.76 for definition A, 2.19 for definition B). However, 59% of the knees meeting MRI definition A and 64% meeting definition B at baseline still did not develop radiographic osteoarthritis over 11 years.

Additional analyses showed:

• 33% of the knees with baseline MRI osteoarthritis by definition A developed KL grade ≥ 2 plus joint space narrowing compared with 13% of the knees without MRI osteoarthritis.
• 28% positive by definition B developed KL grade ≥ 2 plus joint space narrowing compared with 13% negative.
• 27% positive by definition A developed KL grade ≥ 2 plus frequent knee symptoms compared with 11% negative.
• 23% positive by definition B developed KL grade ≥ 2 plus frequent knee symptoms compared with 11% negative.
• Results were consistent across subgroups based on sex, body mass index (BMI), and baseline frequent knee symptom status.

The 1,621 participants had a mean age of 58.8 years and BMI of 27.2 kg/m² and 59.5% of them were women. MRIs were assessed using the MRI Osteoarthritis Knee Score (MOAKS), a validated semiquantitative scoring system evaluating cartilage damage, osteophytes, bone marrow lesions, meniscal damage, and meniscal extrusion.

The study suggested that while current MRI-based definitions of knee osteoarthritis were associated with an increased risk of incident radiographic disease, they may have limited predictive value on an individual level, as many knees meeting these definitions did not develop radiographic osteoarthritis over 11 years.

Disclosures can be found in the study.