How common is Osteonecrosis
• An estimated 10,000 to 30,000 new cases develop each year in the United States. Femoral head ON accounts for 10% of all total hip arthroplasties.
• In cases of nontraumatic ON, corticosteroid use and alcohol abuse may be responsible for 50% to 70% of cases; in up to 10% to 15% of cases, there is no identifiable risk factor (idiopathic).
• Males are affected more frequently than females at a ratio of approximately 8:1, possibly reflecting a higher incidence of trauma in males.
• Most cases develop in the <50-year-old age group. One exception to this observation is seen in ON of the knee (femoral condyles, proximal tibia), to which women over the age of 50 years are predisposed (female:male ratio of approximately 3:1).