Osteonecrosis of the femoral head commonly occurs in middle-aged adults, with an average onset age of 38 years; 25% of patients are less than 25 years old . There are approximately 20,000 new cases per year. Some patients are systemically ill, but the majority of patients are not. Due to the youth and long life expectancy of this patient population, the cost of this disease in terms of quality of life years lost, labor productivity lost, and expense of lifetime treatment is far higher than the incidence alone would suggest. The etiology of osteonecrosis of the femoral head (ONFH) remains unclear. Many factors with strong associations have been identified. The most common include: long term or high dose steroid use, moderate to heavy alcohol consumption, trauma, and blood clotting disorders. Despite the known associations, there remains a significant group (up to 40% of the total), in whom no association or causative factor can be found.
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