Background Arthroscopy, by allowing direct visualization of the synovial membrane, is the gold standard for the assessment of knee synovitis. Given the fact that it is an invasive procedure, other reliable ways to assess synovitis has developed over the past few years. Ultrasonography (US) is a fast, available and low cost imaging tool and has been validated for detecting knee synovitis (1). Ultrasonographic and arthroscopic findings have been shown to correlate (2). However, few studies have yet assessed the correlation between ultrasonographic and histological findings.

Objectives The aim of this study was to assess the correlation between ultrasonographic scores, arthroscopic scores and histological scores for inflammation and vascularity in knee joint synovitis.

Methods Patients with knee pain and/or effusion were prospectively included. Knee was divided in three compartments (medial, lateral and superior). 1 operator (AN) performed a knee ultrasonography (B mode and Doppler mode) prior to the arthroscopy with a semi-quantitative assessment for degree of synovitis. 1 operator then performed a knee arthroscopy (CO, DJV) and scored macroscopic aspects with a 100-mm visual analogic scale (VAS) blindly from US findings and retrieved biopsies from each compartment. Biopsies were analyzed by 1 operator (UF) blindly from both US and arthroscopic findings and scored for: lining layer hyperplasia, inflammation and vascularity. Statistical analysis was made with non parametric Spearman correlation test.

Results 23 patients were included. 16 had rheumatoid arthritis (RA) (ACR/EULAR 2010 criteria). 3 patients had psoriatic arthritis (PsA) (CASPAR criteria), 3 had osteoarthritis (OA) and 1 had gout. Mean ultrasonographic, arthroscopic and histological scores for both synovitis and vascularity were calculated for each patient. A strong correlation was observed between: US synovitis grade and histological inflammation score (r=0.71; p=0.001), US Doppler grade and histological score for vascularity (r=0.6; p=0,0003); US measured synovial thickness and lining layer hyperplasia (r=0.61; p=0,002). Moreover, high positive correlations were observed for both histological lining layer hyperplasia and inflammation between lateral and medial compartments (r=0,90; p=0,00005 and r=0,66; p=0,014 respectively), lateral and superior compartments (r=0,75; p=0,001 and r=0,51; p=0,048, respectively) and medial et superior compartments (r=0,61; p=0,012 and r=0,62; p=0,010, respectively).

Conclusions B mode and Power Doppler US findings strongly correlate with histological inflammation and vascularity scores in actively inflamed knee joints. Ultrasound is therefore a reliable tool for knee joint assessment of the four most common rheumatological diagnoses - RA, PsA, OA and gout -. Moreover, the histological inflammation and hyperplasia scores highly correlate between the superior, medial and lateral compartments of the knee, highlighting the homogeneity of synovial membrane features within the same joint.

1. Karim Z, Wakefield RJ, Quinn M, Conaghan PG, Brown AK, Veale DJ et al. Validation and reproducibility of ultrasonography in the detection of synovitis in the knee: a comparison with arthroscopy and clinical examination. Arthritis Rheum. 2004;50(2):387–94.

2. Rubaltelli JL, Fiocco U, Cozzi L, Baldovin M, Rigon C, Bortoletto P et al. Ultrasound Med. 1994;13(11):855–62.

Disclosure of Interest None declared