Comparing non-enhanced and enhanced sequences in the assessment of effusion and synovitis in knee OA: associations with clinical, macroscopic and microscopic features

The purpose of this study was to evaluate synovial membrane (SM) inflammation and joint effusion scores by semiquantitative magnetic resonance imaging (MRI) assessment with and without enhanced sequences. Gold standards used for comparison were microscopic examination of SM biopsies for SM inflammation and joint volume measurement (JVM) after arthrocentesis for effusion.

Patients (n = 30) fulfilling ACR criteria for knee osteoarthritis (OA) and requiring joint lavage, were evaluated with MRI: (1) SM inflammation was assessed by Whole-Organ Magnetic Resonance Imaging Score (WORMS) on T2 weighted sequences (T2w) a composite score assessing together synovitis and effusion, and the MRI-synovitis score (based on synovitis thickening in five regions of interest) on a T1-weighted fat sat sequence after contrast agent injection (T1wCE). (2) Joint effusion was evaluated by MRI-effusion score (T1wCE) and the WORMS (T2w). JVM was measured after arthrocentesis, and microscopic SM inflammation was determined in SM samples (n = 86). Correlations between MRI scores and clinical, biologic and histologic parameters were studied.

Both scores for effusion were well correlated [r = 0.82 (0.65-0.91); P < 0.001] and presented excellent intraclass correlation coefficient (ICC) for intra- and inter-observer reproducibility. MRI scores for effusion were well correlated with JVM (r = 0.60 for WORMS and r = 0.59 for MRI-effusion score). Synovitis scores were highly reproducible but moderately correlated (r = 0.63; P < 0.001). Only MRI-synovitis total score (T1wCE) was correlated with SM microscopic inflammation (r = 0.46; P = 0.01) and most strongly infiltration (r = 0.45; P < 0.005).

T2w sequences are adequate in assessing effusion volume in compare to joint volume by arthrocentesis but only T1wCE sequences are able to detect synovitis according to the reference of synovial biopsy.