Ischaemic necrosis

death of tissue caused by a significant reduction in blood supply. When this lesion affects bone, the terms infarction and osteonecrosis are commonly used. A bone infarct usually refers to a necrotic focus in the metaphyseal or diaphyseal regions, whereas osteonecrosis indicates the presence of ischaemic cellular death of bone and bone marrow, and ischaemic necrosis generally applies to areas of epiphyseal or subarticular involvement. Necrotic portions of bone are both aseptic and avascular.

CT scanning, MR imaging, and scintigraphy are particularly useful in identifying ischaemic necrosis, especially of the femoral head (III). Six classic stages can be recognized (Table 1), although they fail to reflect the emerging role of MR imaging in evaluation of this condition. (See femoral head (III:1), Fig. 1)

Ischaemic necrosis, Table 1. Stages of ischaemic necrosis of the femoral head.

0 Suspected necrosis, but no clinical findings and normal radiographs and bone scan
I Clinical findings, normal radiographs and abnormal bone scan
II Osteopenia, cystic areas and bone sclerosis on radiographs
III Crescent sign and subchondral collapse without flattening of the femoral head on radiographs
IV Flattening of the femoral head and normal joint space on radiographs
V Joint space narrowing and acetabular abnormalities on radiographs

Other sites that are highly susceptible to ischaemic necrosis include the humeral head, metaphyseal marrow cavities of the long tubular bones in adults, distal femoral condyles and small bones of the carpus and tarsus.