Avascular necrosisAvascular necrosis (or osteonecrosis) describes a condition where by the blood supply to the femoral head is temporarily disrupted. This temporary arrest of blood flow can occur as a result of serious trauma such as a hip fracture or dislocation but can also occur as a result of taking medication, particulary corticosteroids. The blood supply of the femoral head is reduced which causes localised bone death (bone is a living structure). The process normally causes acute and severe pain and later on within a few weeks or months the bone is taken away or resorbed to be replaced by new bone. It is at this later stage where the process or removing the dead bone causes a weakness of bone just underneath the articular cartilage (subchondral bone). This can result in collapse (subsidence) of the adjacent articular cartilage, joint surface incongruity and later secondary arthritis.
X-ray showing subchonral fracture of the left femoral head due to osteonecrosis or AVN
MRI scan showing high signal in the femoral head
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