Objective To explore the value of dynamic ultrasound combined with 3.0T MRI for diagnosing and typing synovial plica of knee joint.Methods Dynamic ultrasound and 3.0T MRI data of 100 patients with suspected synovial plica of knee joint were retrospectively analyzed.Taking the results of arthroscopy as standards,the efficacy of dynamic ultrasound and 3.0T MRI alone and their combination for diagnosing synovial plica of knee joint were evaluated and compared.The length and thickness of synovial plica of knee joint measured with dynamic ultrasound,3.0T MRI alone and their combination were compared with those of arthroscopy,and the consistencies of the location and classification of synovial plica of knee joint with arthroscopy were analyzed.Results Synovial plica was detected in 70 cases,including 11 cases of supropatellar synovial plica,15 cases of infrapatellar synovial plica,medial patellar in 30 cases and lateral patellar synovial plica in 14 cases,among them type A,B,C and D were classified in 9,35,23 and 3 cases,respectively.No significant difference of sensitivity was found between dynamic ultrasound and 3.0T MRI alone for diagnosing synovial plica of knee joint(P＞0.05),which were both lower than that of their combination(both P＜0.05).The length and thickness of knee synovial plica measured with dynamic ultrasound and 3.0T MRI alone were lower than those measured with their combination and arthroscopy(all P＜0.05),and there was no significant difference between the results of their combination and arthroscopy(both P＞0.05).Dynamic ultrasound,3.0T MRI alone and their combination had high consistency of location(Kappa=0.755,0.826,0.897)and classification of knee synovial plica with those of arthroscopy(Kappa=0.721,0.744,0.860).Conclusion Dynamic ultrasound combined with 3.0T MRI was valuable for diagnosing and typing of synovial plica of knee joint.