Effusion-synovitis is the swelling of knee when excess synovial fluid accumulates around the knee joint. Synovial effusion has been suggested to be associated with osteoarthritis. This analysis reveals that synovial inflammation is likely the result of joint structural abnormalities in established osteoarthritis.

To illustrate the relationships between effusion-synovitis and joint structural deformities among knee osteoarthritis (OA) patients over 24 months. 

A total of 413 patients selected for the analysis. Magnetic resonance imaging was used to assess cartilage defects, bone marrow lesions (BML), cartilage volume, and knee effusion-synovitis volume and score. Radiograph used to determine joint space narrowing (JSN) and osteophytes. Least important change criterion was applied to determine a change in effusion-synovitis volume. Western Ontario and McMaster University OA Index were used to measure knee symptoms. 

Total effusion-synovitis volume improved moderately from baseline to follow up. A positive relationship was seen between change in effusion-synovitis volume and baseline BML, JSN, osteophyte scores, and cartilage defect. Although, neither baseline effusion-synovitis score nor volume invariably estimates the change in the above structures except cartilage volume. In the mixed-effects models, knee effusion-synovitis was negatively associated with cartilage volume loss, while positively associated with BML and cartilage defects. Change in effusion-synovitis volume was positively associated with changes in stiffness and knee pain scores.

Subchondral bone and Knee cartilage abnormalities estimated the change in effusion-synovitis, but effusion-synovitis did not estimated knee structural changes. These outcomes propose that synovial inflammation is expected the outcome of joint structural abnormalities in established OA.