Background Multiple joint pathological changes such as synovial effusion, cartilage and subchondral bone lesions are involved in osteoarthritis (OA). The causal relationship between joint effusion and other knee structural changes was not clear.
Objectives This study aimed to determine the cross-sectional and longitudinal associations between knee joint effusion at different compartments and knee osteoarthritic changes in older adults.
Methods A cohort of 976 randomly selected subjects from local community (mean 62 years, 50% female) was studied at baseline and 416 followed up 2.7 years later. Radiographic knee osteophyte and joint space narrowing (JSN) were assessed using the OARSI atlas. T2-weighted fat saturated magnetic resonance imaging (MRI) was utilized to assess knee effusion at 4 compartments: suprapatellar pouch, central portion, posterior femoral recess, and subpopliteal recess. Cartilage volume, cartilage defects, and bone marrow lesions (BMLs) were measured using MRI at baseline and 2.7 years later. Multivariable generalized linear models with Poisson regression analyses or linear regression were used to estimate prevalence ratios (PR) relative risks (RR) or regression coefficient (β).
Results Cross-sectionally, knee effusion at suprapatellar pouch was associated with total cartilage volume (β=-0.23, p=0.05), cartilage defect presence at any compartment (PR: 1.17, p<0.01), BML presence at any compartment (PR: 1.23, p<0.01), any moderate to severe JSN (PR: 1.44, p<0.01) and any osteophyte (PR: 1.54, p<0.001). Effusion at central portion was associated with cartilage defect presence at any compartment (PR: 1.08, p=0.05), BML presence at any compartment (PR: 1.19, p<0.01). Effusion at posterior femoral recess was associated with cartilage defect presence at any compartment (PR: 1.12, p<0.01). Lastly, effusion at subpopliteal recess was associated with cartilage defect presence at any compartment (PR: 1.10, p<0.01), BML presence at any compartment (PR: 1.12, p=0.02), moderate to severe JSN (PR: 1.28, p<0.01) and osteophyte (PR: 1.27, p=0.03).
Longitudinally, suprapatellar pouch effusion was associated with change in cartilage volume (β=-0.33%, p=0.05), increases in cartilage defects (RR: 1.24, p<0.01), and an increase in BML (RR: 1.24, p=0.04). Effusion at posterior femoral recess was associated with change in cartilage volume (β=-0.48%, p<0.01) increases in cartilage defects (RR: 1.11, p=0.03). Effusion at subpopliteal recess was associated with change in cartilage volume (β=-0.36%, p=0.01), increases in cartilage defects (RR: 1.15, p<0.01). In contrast, effusion at central portion was not significantly associated with any of the above structural changes.
All these analyses were performed after adjustment for age, gender, BMI, rheumatoid arthritis, and/or radiographic osteoarthritis (ROA).
Conclusions Knee joint effusions are associated with knee osteoarthritic structural changes suggesting a potential causal relationship. While suprapatellar pouch effusion is most consistently associated with knee structural changes, central portion effusion is not associated with changes in knee structures over time.
Disclosure of Interest None declared
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