Functional indexes in osteoarthritis of the knee are significantly determined by the presence or not of synovitis

Background: Osteoarthritis (OA) is a common, age-related disorder affecting synovial joints characterized by the loss of articular cartilage with joint space narrowing and subchondral bone reaction. Synovitis may be present in OA joints influencing the development and progression of joint degeneration.
Objectives: To evaluate the prevalence of synovitis in patients with OA of the knee (ACR criteria), to verify the correlation between synovitis, serum C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), to establish the link between synovitis and clinical features of knee OA (WOMAC Osteoarthritis Index, Lequesne index).
Methods: 109 patients (19M 90F, mean age 67.2±9.1, mean BMI 27.2±5.2, grade > 1 according to the Kellgren and Lawrence scoring system) with primary OA of the knee were enrolled in this study. Ultrasound examination of the knee joints was carried out using a 13-MHz linear probe at the suprapatellar recess. WOMAC Osteoarthritis Index, Lequesne index, CRP serum level and ESR was determined at the time of enrollment.
Results: 39 patients (35,8%) (6M 33F, mean age 67.4±9.9, mean BMI 28.8±4.9) had synovitis (synovial thickness > 1,5mm). 70 patients (13M 57F, mean age 68.9±8.5, mean BMI 26.7±4.1) did not. We found a statistically significant difference between the two groups in the following items: ESR (p=0.001), CRP (p<0.0001), WOMAC (p=0.005) and Lequesne (p=0.0005). There was no correlations between BMI scores and CRP serum levels in both groups. Moreover, Kellgren and Lawrence scoring system was similar in synovitis and no-synovitis patients: 2.6±0.7 vs 2.6±0.8 respectively.
Conclusion: We found an high prevalence of synovitis in knee OA, that significantly influenced the functional indexes. CRP serum level correlates stronger than ESR with knee synovitis.