Association of Knee Effusion Detected by Physical Examination With Bone Marrow Lesions: Cross‐Sectional and Longitudinal Analyses of a Population‐Based Cohort

Objective To determine the association of effusion detected by physical examination with the prevalence of bone marrow lesions ( BML s) on magnetic resonance imaging ( MRI ), and the incidence/progression of BML s over 3 years in subjects with knee osteoarthritis. Methods A population‐based cohort with knee pain (n = 255) was assessed for effusion on physical examination. On MRI , BML s were graded 0–3 (none, mild, moderate, severe), and incidence/progression was defined as a worsening of the sum of BML scores over 6 surfaces by ≥1 grade. We analyzed the full cohort and a mild disease subsample with a Kellgren/Lawrence (K/L) grade <3. Cross‐sectional logistic and longitudinal exponential regression analyses were performed, adjusted for age, sex, body mass index ( BMI ) and pain. We calculated sensitivity, specificity, positive predictive value ( PPV ), and negative predictive value ( NPV ) for effusion detected by physical examination versus BML s (prevalence and incidence/progression). Results The weighted mean age was 56.7 years, the mean BMI was 26.5, 56.3% were women, 20.1% had effusion on physical examination, and 80.7% had a K/L grade <3. Effusion on physical examination was significantly associated with prevalent BML s in the full cohort (odds ratio [ OR ] 6.10 [95% confidence interval (95% CI ) 2.77–13.44]) and in the K/L grade <3 cohort ( OR 6.88 [95% CI 2.76–17.15]). In the full cohort, sensitivity, specificity, PPV , and NPV were 34.6, 92.5, 79.9, and 62.1%, respectively, and in the K/L <3 cohort 31.7, 94.0, 75.5, and 70.1%, respectively. Longitudinally, effusion on physical examination was not significantly associated with BML incidence/progression in the full cohort (hazard ratio [ HR ] 1.83 [95% CI 0.95–3.52]) or in the K/L grade <3 cohort ( HR 1.73 [95% CI 0.69–4.33]). In the two cohorts, sensitivity, specificity, PPV , and NPV were 32.0, 82.2, 42.2, and 74.9%, respectively, and 21.2, 85.6, 30.1, and 78.8% respectively. Conclusion BML s on MRI can be predicted from physical examination effusion cross‐sectionally, with a high PPV of 79.9%. Assessment for knee effusion on physical examination is useful for determining potential candidates with BML s before costly MRI screening for recruitment into clinical trials.