The University of Pennsylvania Classification of Osteonecrosis

The management of osteonecrosis (ON) remains one of the more perplexing problems facing the orthopedic surgeon. There is still much to be learned about the etiology, pathophysiology, and management of this condition. Because prognosis and treatment are determined in large part by the stage of the disease, it is important to use a reliable and efficient method of evaluation and staging. The uniform use of such a system of classification would also enable us to compare the effectiveness of various methods of treatment and determine the best method of management for different stages of osteonecrosis.