Antigen-induced arthritis in rabbits: a comparative study between high-resolution ultrasound and contrast-enhanced ultrasound and pathologic findings

The objective of this study was to explore the feasibility and value of high-resolution ultrasound and contrast-enhanced ultrasound in evaluation of synovitis in rabbit knee joint in antigen-induced arthritis (AIA). Thirty-six rabbits were divided into three groups, each injected with different doses of ovalbumin (OVA) into the right knee joint. On week 1 and 4, 6 randomly selected in each group were killed. Each knee joint undergone the high-resolution ultrasound to measure capsule thickness and contrast-enhanced ultrasound to measure synovium thickness. The results from the ultrasound examinations were compared with those of pathologic examinations. Different OVA doses resulted in different modeling success rate, different pathological synovitis score, and different capsule and synovium thickness measured by ultrasound. The diagnostic accuracy of synovitis by ultrasound was high. The ultrasound measurement revealed that the capsule thickness on week 4 was lessened than that on week 1, while the synovial thickness on week 4 was greater than that on week 1. Both the joint capsule and synovium thickness measured by ultrasound were significantly and positively correlated to the pathologic synovitis score (P < 0.05). The synovial thickness on week 4 is more correlated to the synovitis score than the capsule thickness, rather than that on week 1. Injection of OVA of different doses results in different modeling success rate and synovitis severity. The high-resolution ultrasound and contrast-enhanced ultrasound can be used to determine whether the AIA was made successfully and evaluate the synovitis severity. In chronic inflammatory phase, the contrast-enhanced ultrasound has better effect.