Fig. 8.

Radiological pattern of a “mobile” subchondral fracture, pathognomonic for necrosis. a On CT arthrography, a very thin fracture/separation in the subchondral trabecular bone appears as a radiolucent line (“eggshell dissection”) (arrow). b A few months later, a radiograph shows a collapse of the condyle lower pole (arrow) with breaks in the continuity of the subchondral bone plate (arrowheads). c An additional radiograph performed by fluoroscopy and with traction on the leg shows a slight opening of the subchondral bone dissection (arrow)