In a study on multifocal osteonecrosis [67], plain radiography or MRI revealed that most (69 %) joints presented in a precollapse stage. Eighty-five of 200 (43 %) hips had collapse (59 hips) or osteoarthritis (26 hips). Only 17 % of 179 knees, 38 % of 146 shoulders, and 24 % of 71 ankles had collapse or arthritis. Approximately 30 % of the lesions were diagnosed solely by MRI. There was a higher incidence of these asymptomatic lesions in the knee (38 %), shoulder (30 %), and ankle (44 %) than in the hip (18 %). The incidence of negative radiographic findings but positive MRI scans was highest in the ankle (44 %) and knee (38 %) and lower in the shoulder (30 %) and hip (18 %).

In summarizing the epidemiology of osteonecrosis in the USA, it is evident that the prevalence and incidence vary according to the risk factor of disease and the population being studied. Traumatic osteonecrosis is associated with specific fractures, and the incidence depends upon many factors such as age, displacement, type of fracture, and method of treatment. Nontraumatic ONFH can be idiopathic but is usually associated with corticosteroid usage, ethanol abuse, systemic lupus erythematosus, barotrauma, or marrow packing disorders such as sickle cell disease and Gaucher’s disease. The proportion of patients with steroid-related ONFH is increasing as solid organ and bone marrow transplantation are becoming more commonplace.