To compare the advantages and disadvantages between ultrasound (US) and magnetic resonance imaging (MRI) in the diagnosis of hip joint effusion, in order to provide a basis for the clinical rational choice of imaging examination methods.

From November 2018 to January 2020, 132 patients with clinically confirmed synovitis of the hip joint who were scheduled to receive intra-articular drug injection at Peking University Third Hospital were selected as the study subjects. The clinical and imaging data of all patients were retrospectively analyzed, and the number of cases and degree of hip effusion diagnosed by ultrasound and MRI were compared by Pearson χ² test and Student t test, which were then compared with the final clinical diagnosis.

US indicated that 59 patients (44.70%, 59/132) had joint capsule swelling, joint recess effusion, or surrounding soft tissue swelling. MRI examination reported joint synovial thickening, joint effusion, bone marrow edema, and surrounding soft tissue swelling in 92 patients (69.70%, 92/132). The positive rate of hip effusion detected by MRI (69.70%) was significantly higher than that of ultrasound (44.70%; χ²=6.294, P=0.015). However, the fluid depth of joint effusion in sonopositive patients was significantly greater than that detected by MRI [(7.60±1.81) mm vs (5.32±0.94) mm, t=3.155, P=0.003].

MRI is more effective in diagnosing hip joint effusion with a small amount of fluid, while US has a better diagnosis of hip joint effusion with a large amount of fluid and can be used as a supplementary examination.