Background Synovitis is prevalent in knee OA and is an important determinant of pain.
Objectives To better understand the nature of synovitis and its association with pain we investigated patterns of synovitis on contrast enhanced (CE) MRI and its relation to pain and radiographic severity.
Methods 91 patients (mean (SD) age 62 (7.5) years, 68% woman, BMI median (IQR) 29 (26-31) kg/mm2, median (IQR) Kellgren-Lawrence score 3 (2-4)) with symptomatic knee OA attending the rheumatology or orthopedic outpatient clinic were included. 55 patients underwent arthroscopy and 36 arthroplasty. Sagittal and axial T1-weighted CE MRI images (3T) were used to semi-quantitatively score synovitis at 11 sites (total range 0-22) according to Guermazi et al.1 (Ann Rheum Dis 2011). Self-reported pain was assessed by visual analogue scale (VAS, 0-100), knee injury and osteoarthritis outcome score (KOOS (subscale pain),0-100) and measure of intermittent and constant osteoarthritis pain (ICOAP, intermittent pain (0-100), constant pain (0-100)). Principal component analysis (PCA) with varimax rotation and Keiser Normalization was used to investigate patterns of synovitis for all patients. A factor was said to load significantly on a component when loading exceeded 0.4. Subsequently, different patterns were associated with pain measures in linear regression analysis adjusted for gender and age using SPSS 20.0. Log transformations were used when appropriate.
Results A mild synovitis was observed (median (IQR) 7.0 (5-10)). Mean (SD) KOOS pain was 51.8 (23.3). Median (IQR) VAS was 53.0 (32-70) and ICOAP constant pain 35.0 (15.0-55.0) and ICOAP intermittent pain 45.8 (25-60.4). PCA resulted in extraction of 3 components (Eigen value > 1), together explaining 53.7% of variance. Component 1 was characterized by synovitis at 7 sites with mainly medial parapatellar involvement associated with KOOS pain, ICOAP constant pain and radiographic severity, not with VAS and ICOAP intermittent pain. Component 2 was characterized by synovitis at site adjacent to the anterior cruciate ligament, medial parameniscal site, intercondylar site and suprapatellar site, but did not associate with any of the pain measures nor with radiographic severity. Component 3, characterized by synovitis at 3 sites (mainly characterized by synovitis loose body site), was also associated with radiographic severity.
Conclusions Different patterns of synovitis in knee OA were observed. Our results suggest that a certain synovitis pattern is associated with pain, providing important insights into mechanisms underlying osteoarthritic knee pain.
Guermazi A, Roemer FW, Hayashi D, Crema MD, Niu J, Zhang Y et al. Assessment of synovitis with contrast-enhanced MRI using a whole-joint semiquantitative scoring system in people with, or at high risk of, knee osteoarthritis: the MOST study. Ann Rheum Dis 2011;70:805-11.
Disclosure of Interest None Declared