**2. Etiology**

The term osteonecrosis means, "bone necrosis." Necrosis is a histopathological event that can occur after four types of injury:


When we refer to osteonecrosis in orthopedics, we are actually using the term for circulatory lesions that affect the bone, which would be better called "infarction." Necrosis caused by circulatory injury may be due to


In 1915, Phemister described and differentiated histological changes from necrosis caused by infection (septic necrosis) of those caused by circulatory changes (aseptic necrosis).

Regardless of the predisposing factor, the cause of osteonecrosis is always the inadequate blood perfusion of the bone [3]. Bone is a rigid and nondistensible tissue. Besides that, subchondral limited collateral circulation on the convex side of articular surfaces and decreased perfusion pressure of all epiphyses, which helps to explain the higher incidence of osteonecrosis in some regions of the skeleton.
