Magnetic resonance imaging of medial fat pad in knee explaining dry tap

Failed arthrocentesis due to focal triangular fat pad. T2 weighted axial image through the mid-pole of the patella shows a prominent triangular fat pad located in the notch of the medial aspect of the patellofemoral joint (white arrow). A 1.5-inch needle (long arrow) could only reach the joint effusion in this relatively thin patient if the needle were placed to the hub.