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Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed
Idiopathic avascular necrosis of femoral head. Goes through 5 phases: (1) Initial - histological evidence of dead bone with disappearance of osteocytes from empty lacunae, (2) Early - incipient revascularization, (3) early intermediate - active resorption of dead bone along with new bone deposits (4) late intermediate- decreased bone resorption and increasing immature bone formation, (5) formation of mature haversian systems.
Take neutral and frog leg views of the pelvis. Radiographically goes through 5 phases on plain film: (1) Initial - earliest finding is a non specific joint effusion, (2) Early - see subchondral fractures in the anterolateral aspect of the femoral epiphysis along with a slight increase in density, (3+4) Intermediate - granular or fragmented appearance of the femoral epiphysis with 33% of patients developing cyst like demineralization in the metaphysis and the unprotected epiphysis develops gradual flattening and lateral extrusion of cartilage leading to broadening of femoral neck, and (5) Late - immature bone is replaced by remodeled trabecular bone. The final appearance of the femoral head can be normal or flattened (coxa plana) with short wide femoral neck (coxa magna).
On MRI abnormal low signal is seen on T1WI and T2WI during the infarction / necrosis stage that can be uniform or patchy in the epiphyses and metaphyses. During the fragmentation repair stage high and low intermixed areas of signal can be seen and as revascularization and reossification proceed the epiphysis is restored to a more uniform high signal intensity region.
Avascular Necrosis of the Femoral Heads:
See References Chapter.
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