Fig. 1

Synovial chondromatosis of the left knee. Lateral radiograph showing a large calcified mass in the posterior aspect of the left knee, with small calcific foci anteriorly. Photomicrograph (bottom image) showing the classical multinodular pattern of synovial chondromatosis with areas of calcification and endochondral ossification. FISH analysis shows break-apart signals using ACVR2A probe (top right)