Fig. 18.

Early subchondral insufficiency fracture with osteonecrosis (SIF-ON) and collapse. a T1-weighted MR image shows an area of low signal intensity in the inferior pole of the medial condyle (arrow). b T2-weighted image (b) shows an immediate subchondral low signal intensity area longer than 14 mm (arrowheads), suggestive of early SIF-ON. Note also several fissure lines away from the surface (arrow), which is also a risk factor for an evolution towards a SIF-ON. c A few years later, a radiograph shows an irregular collapsed articular surface, confirming the initial suspicion of SIF-ON