Background/Purpose: Inflammation has been implicated in the pathogenesis of KOA, but the relevance of physical exam findings and patient-reported symptoms of inflammation is unknown. Our objectives were to examine the association between physical exam findings, including bulge sign and patellar tap, as well as participant-reported symptoms, with MRI-detected effusion-synovitis (ES) in two samples: knees that developed radiographic OA (ROA) and knees that went on to knee replacement (KR).

Methods: The Osteoarthritis Initiative (OAI) is a longitudinal cohort study of participants with or at risk for ROA. Two samples with available MRI readings were utilized: 355 knees that developed incident ROA within 4 years of follow-up (323 participants) and 225 knees that underwent KR within 5 years of follow-up (195 participants). The bulge sign and patellar tap were conducted by trained examiners at baseline, 2 years, and 4 years. Questionnaires assessing participant-reported knee swelling and knee pain when straightening fully, in the last 7 days, were administered at the same visits. MRI was performed with 3-T systems (Trio; Siemens, Erlangen, Germany). Non-contrast effusion-synovitis (ES) was scored using the MRI Osteoarthritis Knee Score (MOAKS). Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CI) to assess the association between physical exam findings and participant-reported symptoms with MRI-detected ES, with generalized estimating equations to account for two knees in an individual and multiple time points.

Results: The 323 participants in the ROA group were predominantly female (66%), overweight and obese (42%, 39% respectively), white (81%), with mean age 60 years. The 195 participants in the KR group were also largely female (58%), overweight and obese (37%, 47% respectively), white (86%), with mean age 65 years. Among knees that developed ROA, those with bulge sign or patellar tap had significantly higher odds of ES, compared to those without these findings (OR=3.67 [95%CI: 2.43, 5.54]).  In addition, among knees that went on to KR, a modest association was found with presence of these findings (OR=1.91 [95%CI: 1.28, 2.85]). Knees with participant-reported swelling in the last 7 days, and pain when straightening fully had significantly higher odds of ES, with evidence of dose-response based on the frequency of swelling, and severity of pain, in both ROA knees, and KR knees (Figure 1).

Conclusion: A bulge sign and patellar tap on physical exam were associated with MRI-detected ES, as well as participant-reported knee swelling and knee pain when straightening fully in participants who developed ROA as well as those who progressed to KR. The magnitude of association was greater for frequent and severe self-reported symptoms, compared to physical exam findings, and among early OA knees compared to end-stage OA knees when ES was more prevalent.