Fig. 2

The MRI images of the right knee from different positions. (a1-d1) In the first hospitalization, the MRI images showed a large amount of fluid signal shadow in the right knee joint cavity from different positions, including the lateral sagittal position (a1, T1WI; c1 PDWI), the transverse axial position (b1, T2WI) and the coronary position (d1, PDWI). (a2-d2) During the second hospitalization, the MRI images highlighted patchy high signal shadows (white arrows) in the surrounding soft tissues of the right knee (observed in a2, T1WI; b1, T2WI; c2 PDWI; d2 PDWI-COR). A patchy low T1-weighted signal (a2) and high PD-weighted fat-suppressed signal (c2, d2) were seen in the distal metaphysis of the right femur and proximal metaphysis of the tibia, with unclear borders. Fluid signal shadows and strip-like signal shadows were seen within the right knee joint cavity. Abbreviations: T1WI, T-weighted image; T2WI, T2-weighted image; PDWI, proton density-weighted image; PDWI-COR, coronary proton density-weighted image