Differentiation of subchondral insufficiency fractures from osteonecrosis

Osteonecrosis and subchondral insufficiency fractures rely on different pathomechanisms. Osteonecrosis is based on an insufficient blood supply of the bone, and thus may occur multifocal. The blood supply in subchondral insufficiency fractures is intact, however, the bony architecture is disturbed. Therefore, even normal load weakens the bone and may lead to a fracture. Beside clinical history, the shape of the demarcation-or fracture-line in relation to the joint surface on radiological images is characteristic. Bone marrow edema is evident in both entities and can be considered as a risk factor for collapse of the articular surface in osteonecrosis. Additionally, the extent of osteonecrosis or insufficiency fractures should be reported, as it affects prognosis and therapy. Initial radiographs may be unremarkable. Therefore, MRI is crucial for early stage diagnosis and timely treatment in order to prevent from articular surface collapse and secondary osteoarthritis.