Anatomical distribution of synovitis in knee osteoarthritis and its association with joint effusion assessed on non-enhanced and contrast-enhanced MRI.

PURPOSE: To describe the anatomical distribution of synovitis and its association with joint effusion on non-enhanced and contrast-enhanced (CE) MRI in patients with knee osteoarthritis (OA). METHODS: Baseline MRI was performed at 1.5T using axial proton density (PD)-weighted (w) fat suppressed (fs) and axial and sagittal T1-w fs CE sequences. Synovial enhancement was scored in nine articular subregions. Maximum synovial enhancement was grouped as absent (0), equivocal (1) and definite (2 and 3). Effusion was scored from 0 to 3 on the axial sequences. We described the anatomical distribution of synovitis, its association with effusion and compared assessment of effusion on T1-w fs CE and PD fs sequences. RESULTS: 111 subjects were included and examined by MRI. 89.2% of knees exhibited at least one subregion with a minimum grade 2 and 39.6% at the maximum of a grade 3. The commonest sites for definite synovitis were posterior to the posterior cruciate ligament (PCL) in 71.2% and in the suprapatellar region in 59.5% of all knees. On T1-w fs CE, 73.0% of knees showed any effusion. Definite synovitis in at least one location was present in 96.3% knees with an effusion and in 70.0% without an effusion. Higher grades of effusion were scored on the PD fs sequence. CONCLUSION: Definite synovitis was present in the majority of knees with or without effusion with the commonest sites being posterior to the PCL and in the suprapatellar recess. Joint effusion as measured on PD fs images does not only represent effusion but also synovial thickening