Joint effusions: MR imaging.

Magnetic resonance (MR) images of the hips and knees of three healthy volunteers were reviewed and compared with images obtained from the hips of three patients with effusions. Comparison was also made with MR images obtained from two swine knees following the injections of saline in one and blood in the other. The anatomy of the knees and hips was well defined. The hip effusions were all easily recognized. MR images of the swine knees clearly demonstrated the experimentally produced joint effusions. The hip effusions and the experimentally introduced blood and saline all had long T1 and T2 values allowing easy differentiation from articular cartilage. We were unable to distinguish fresh blood from saline in the knee joints.