- There is patchy loss of normal T1 marrow signal and associated subtle T2 hyperintensity in the femoral head, which represent nonspecific bone marrow edema. In a patient with chronic steroid use, these findings are very suspicious for osteonecrosis of the femoral head.
- Scroll through the T1 sagittal and T2 coronal sequences and follow the subchondral, crescentic shaped line that is T1 dark and T2 hyperintense - this line represents a prominent subchondral fracture along the anterosuperior surface of the femoral head.
- Note the mild flattening of the femoral head on the sagittal sequence, suggestive of early articular surface collapse.
- You can also look at the original plain film of the case and see a very subtle subchondral lucency along the femoral head which corresponds to the subchondral fracture.
Remember this mnemonic for causes of osteonecrosis:
A = anemia (Sickle cell)
S = steroids
E = EtOH
P = pancreatitis
T = trauma
I = idiopathic
C = Caisson's disease (dysbaric syndrome)