ObjectiveTo access the anti-inflammatory effect of kidney-supplementing cold-dispelling Zhiwang Decoction (Zhiwang Decoction) combined with methotrexate (MTX) on collagen-induced arthritis (CIA) model rats and the performance of high frequency ultrasound in the evaluation of arthritis in rats.MethodsSD rats were randomly divided into 5 groups: normal group, model group, MTX group, low-dose of Zhiwang Decoction combined group and high-dose of Zhiwang Decoction combined group. Except for the normal group, rats of the other groups were injected in the tail with 50 μL collagen Ⅱ emulsion of 2 mg/mL on the 7th and 14th day of rearing respectively. A total of 21 days of administration began on the 8th day. Toe thickness was measured, arthritis index (AI) was scored and ankle synovitis was evaluated by high-frequency gray-scale ultrasound in rats.ResultsAfter modeling, the toe thickness of each group was significantly thicker than that of the normal group (P<0.01). on the 19th day, the toe thickness of the high-dose combined group was thinner than that of the model group (P<0.05). In terms of AI score, on the 13th day, the AI score of the high-dose combined group was lower than that of the model group (P<0.01). Evaluated by the ultrasound, the synovial thickness of each group was significantly thicker than that of the normal group, the synovium of the low-dose and high-dose groups was significantly thinner than that of the model group, and the synovium of the high-dose group was significantly thinner than that of the MTX group (P<0.05, p < 0.01).ConclusionHigh-frequency ultrasound is suitable for the evaluation of synovitis in CIA model rats, and its sensitivity is better than toe thickness and AI score. High-dose Zhiwang Decoction combined with MTX has a synergistic effect on improving arthritis in CIA rats.