Fig. 2
From: Synovitis in osteoarthritis: current understanding with therapeutic implications
a Sagittal fat-suppressed proton density-weighted image (non-CE-MRI) shows hyperintensity in the intercondylar (arrow) region of Hoffa’s fat pad. This signal alteration is used as a surrogate marker for synovitis on non-CE-MRI. There is a discrete subchondral bone marrow alteration in the femur (arrowhead) corresponding to the site of the anterior cruciate ligament (ACL) insertion. b In contrast, sagittal fat-suppressed T1-weighted contrast-enhanced MRI (CE-MRI) shows no intercondylar synovitis, but reveals infrapatellar synovitis and synovitis adjacent to the tibial ACL insertion (arrows) not seen on non-CE-MRI, as well as bone marrow edema (arrowhead). c Axial non-CE-MRI shows a fluid-equivalent signal within the joint cavity suggestive of joint effusion in the peripatellar recesses (arrows) and posteriorly (arrowhead). d Axial CE-MRI shows marked synovitis anteriorly (arrows) and true effusion only depicted posteriorly as hypointensity adjacent to the synovial lining (arrowhead). Reprinted from [62] with permission from Elsevier