Background Knee pain is a prominent symptom of osteoarthritis (OA). Joint synovial effusion could contribute to pain, but the relationship between them remains controversial. In addition, the effects of joint effusions at different knee compartments on knee pain are unclear.
Objectives Aim of this study was to determine the cross-sectional and longitudinal associations between knee joint effusions at different compartments and knee pain in older adults.
Methods Population-based cohort study of older adults randomly selected from local community (N=976, mean age 62.3 years, range from 50 to 80; 50.1% females). Knee joint effusions were measured at baseline using T2 weighted magnetic resonance imaging (MRI) at 4 compartments (suprapatellar pouch, central portion, posterior femoral recess, and subpopliteal recess). Other structural changes including cartilage defects, bone marrow lesions and meniscal lesions were assessed by MRI. OARSI atlas was used to assess knee osteophytes, joint space narrowing (JSN) and radiographic OA. Knee pain was assessed by self-administered Western Ontario and McMasters osteoarthritis index (WOMAC) questionnaire at baseline and 2.6 years later. The 5 WOMAC pain subscales were clinically constructed into weight-bearing pain and non-weight-bearing pain. Univariable and multivariable logistic regression analysis and generalized linear models with Poisson regression analysis were used to estimate prevalence ratios (PR) or relative risks (RR) for the association between knee effusion (0-3) and baseline or increases in knee pain.
Results Prevalence of knee joint effusion (≥2) was 42.9% at suprapatellar pouch, 48.8% at central portion, 10.3% at posterior femoral recess and 14.4% at subpopliteal recess. Cross-sectionally, knee effusion at suprapatellar pouch was significantly associated with total (PR: 1.26, 95% CI 1.08 to 1.48) and non-weight bearing knee pain (PR: 1.24, 95% CI 1.06 to 1.46), but not with weight-bearing pain, after adjustment for age, gender, BMI, rheumatoid arthritis, radiographic OA and other knee structures. Joint effusions at other compartments were not significantly associated with knee pain.
Longitudinally, effusion at suprapatellar pouch was associated with increases in total (RR: 1.20, 95% CI 1.00 to 1.44), non-weight-bearing (RR: 1.38, 95% CI 1.09 to 1.75) and weight-bearing knee pain (RR: 1.26, 95% CI 1.04 to 1.53) after adjustment for above covariates. Effusions at posterior femoral recess and central portion were associated with increases in non-weight-bearing knee pain (RR: 1.55, 95% CI 1.25 to 1.91 and RR: 1.29, 95% CI 1.01 to 1.65; respectively) but not with weight-bearing knee pain. Effusion at subpopliteal recess was significantly associated with an increase in total knee pain (RR: 1.16, 95% CI 1.01 to 1.32) after adjustment for age, sex and BMI, but became non-significant after further adjustments.
Conclusions Knee joint effusions have independent compartment-specific associations with knee pain in older adults. Suprapatellar pouch effusion is associated with both non-weight-bearing and weight-bearing knee pain, while posterior femoral recess and central portion effusions are only associated with non-weight-bearing knee pain.
Acknowledgements We especially thank the participants who made this study possible, and we gratefully acknowledge the role of the Tasmania Older Adult Cohort staff and volunteers in collecting the data.
Disclosure of Interest None declared