Background/Purpose: Histological analysis of synovial tissue, despite being a reliable and accurate assessment for synovitis, is not routinely performed. Ultrasonography (US) is a fast, available and low cost imaging tool and has been validated for detecting synovitis. Ultrasonographic and macroscopic findings at arthroscopy have been shown to correlate well. However, a few studies have assessed the correlation of ultrasonographic and immunophenotypic features of synovial tissue, with contradictory results and mostly on long lasting rheumatoid arthritis patients. The aims of this study were (a) to assess the correlation between ultrasonographic and histological scores for inflammation and vascularity in knee joint synovitis; and (b) to evaluate the strength of the correlation for both inflammation and vascularity scores in the 3 major compartments of the knee using US, arthroscopic and histological evaluation.

Methods:  Patients of an early arthritis cohort were prospectively included in the study. One operator (AN) performed a knee ultrasonography (B mode and Power Doppler mode) of the three major compartments (medial, lateral and superior) prior the arthroscopy. B mode synovitis grade and Power Doppler activity were scored semi-quantitatively. A different operator (CO/DV) then performed a knee arthroscopy and scored macroscopic aspects with a 100-mm numeric scale (NS) blinded to the US findings. Biopsies were obtained from each compartment, stained with standard H&E, CD68 and Factor VIII, and then analyzed by another operator (UF) blinded to both the US and arthroscopic findings and scored for lining layer hyperplasia, inflammation and vascularity. Statistical analysis was made with non parametric Spearman correlation test.

Results: 26 patients were included. 17 had rheumatoid arthritis (RA) (ACR/EULAR 2010 criteria). 3 patients had psoriatic arthritis (PsA) (CASPAR criteria), 4 had osteoarthritis (OA), 1 had gout and 1 had undifferentiated arthritis. 17 patients (65.4%) were untreated at inclusion. Strong correlations were observed between: US synovitis grade and histological inflammation score (r=0.60; p=0.002), US Power Doppler grade and histological score for vascularity (r=0.69; p<0.001); US measured synovial thickness and lining layer hyperplasia (r=0.61; p=0.002); US synovitis grade and CD 68 score (r=0.49; p=0.02). The findings were homogeneous within the joint as high positive correlations were observed for both histological lining layer hyperplasia and inflammation between lateral and medial compartments (r=0,95; p<0,0001 and r=0.68; p=0.014 respectively), lateral and superior compartments (r=0.78; p=0.001 and r=0.51; p=0.048, respectively) and medial and superior compartments (r=0.69; p=0.004 and r=0.69; p=0.004, respectively).

Conclusion: B mode and Power Doppler US findings strongly correlate with histological inflammation and vascularity scores in actively inflamed knee joints. Ultrasound is therefore an accurate tool for knee joint synovitis assessment of the four most common rheumatic disease diagnoses – RA, PsA, OA and gout.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/synovial-immunophenotype-and-ultrasonography-a-contemporaneous-study-of-different-compartments-of-the-knee-joint/