The main diagnostic criteria include gray-scale ultrasound and energy Doppler ultrasound. The diagnostic criteria of gray-scale ultrasound are divided into 0-Ⅲ levels, with level 0 meaning completely normal; level I meaning hypoechoic area on the bone level line of the joint cavity; level II meaning the echogenic area beyond the bone level line and the upper end is depressed or horizontal; level III meaning the upper end of the hypoechoic area is raised. The diagnostic criteria of energy Doppler ultrasound are divided into grade 0-III. Grade 0 refers to the absence of any blood flow signal; grade I refers to the blood flow signal in the form of three dots; grade II refers to the amount of blood flow signal not exceeding 50% of the joint cavity; grade III refers to the area of blood flow signal greater than 50% of the joint cavity.