Synovitis in knee osteoarthritis (OA) patients is a significant risk factor for disease progression. This study aimed at developing a magnetic resonance imaging (MRI) scoring system allowing reliable and sensitive assessment of synovitis severity in knee OA patients without the use of a contrast agent.
Imaging was performed without contrast agent, using a 1.5T and a knee coil. For the synovial membrane, the MRI exam included two axial sequences: a T2-weighted (synovial fluid) and a gradient echo (GRE) (synovial membrane). Synovial membrane thickness was measured on four regions of interest (ROI): medial and lateral recesses, and medial and lateral suprapatellar bursa, with each graded/scored from 0 to 3, for a maximum of 12. A validation study was performed on a cohort of 27 knee OA patients having MRI at baseline. A subset of 14 patients had an additional MRI acquisition and symptom assessment at Day 60. Evaluation of disease symptoms was done with Western Ontario and McMaster Universities OA Index and visual analog scale, and of cartilage volume, menisci and subchondral bone, with MR images from a 3D spoiled gradient recalled (SPGR) sequence.
The synovial membrane thickness grade was 1.9+/-0.5 (mean+/-SD) with a score of 7.1+/-2.3. The intra-reader (r=0.91) and inter-reader (r=0.82) correlation coefficients were excellent (P<0.0001). The medial compartment grade was 1.9+/-0.6 and score was 3.4+/-1.4, and of the lateral compartment were 2.0+/-0.7 and 3.7+/-1.5, respectively. The grade and score for the suprapatellar bursa and recess were 1.8+/-0.7 and 3.5+/-1.5, and 2.1+/-0.5 and 3.9+/-0.9, respectively. No statistically significant differences in the ROI score and grade were observed between medial and lateral compartments or between recess and suprapatellar bursa. A positive correlation was found between the global severity of synovitis at baseline and the presence of a medial meniscal extrusion (P<0.04), and the loss of cartilage volume at 60 days (P<0.03).
This newly developed MRI technology for the assessment of synovial membrane thickness in knee OA patients was shown to be accurate and reproducible.