Osteonecrosis of the femoral head: diagnosis and classification systems

Osteonecrosis of femoral head is a rare but disabling condition that usually results in progressive femoral head collapse and secondary arthritis necessitating total hip arthroplasty if not treated appropriately in early stages. However, early diagnosis is challenging as the onset of disease is insidious and the symptoms and signs are usually minimal and nonspecific until it becomes advanced. Of several diagnostic modalities, magnetic resonance imaging (MRI) is considered the imaging method of choice with the highest sensitivity and specificity, while detection of potential risk factors is very important as well. Many investigators have developed several different classification systems; however, there still is controversy regarding the optimal classification system. Diagnostic methods and the evolution of different classification systems will be reviewed in this paper.