Sixty-five-year-old female with complaint of spontaneous acute pain at the lateral aspect of the knee

Excerpt

Radiographs show a round, well-defined soft tissue calcification with some heterogeneity within. It is located on the lateral aspect of the external femoral condyle, above the insertion of the popliteal tendon, and associated with subtle cortical erosion of adjacent bone. Eight days later, MRI T2-weighted and STIR images on coronal and axial planes show a cortical-subcortical hypointense lesion surrounded by marked bone marrow edema. The biceps femoris tendon is intact while the gastrocnemius insertion and the more proximal fibers of the collateral lateral ligament show moderate thickening and a mildly increased signal intensity. The surrounding soft tissues are significantly inflamed. Subsequent computed tomography (CT) examination sites the peritendinous calcification between the origin of the lateral gastrocnemius tendon, the lateral collateral ligament, and the biceps femoris. …