The incidence of ON is unknown. Many early cases are probably not diagnosed, and many late cases are probably misdiagnosed as osteoarthrosis. About 5–10% of total hip replacements (THA) are performed due to ON . Jacobs  found that treatment with corticosteroids (28%) and alcoholism (39%), and diseases like Gauchers disease, sickle cell disease, decompression sickness and primary Cushings disease are the most common conditions associated with ON. In 25% no associated conditions or diseases could be found. More than 3/4 of the patients are men in the third to fifth decade, and in more than half the cases both hips are affected .