A 10-year-old boy complains of increasing pain in his left hip. He began limping shortly after playing a baseball game at school. He is afebrile. An X-ray of the femoral head shows a fracture and irregular densities of the cancellous bone. You make a diagnosis of Legg-Calve-Perthes disease. Which of the following best describes the pathologic findings in this patient?

Osteonecrosis, also known as avascular necrosis, refers to the death of bone and marrow in the absence of infection. Such bone infarcts may be caused by a variety of conditions, such as trauma, thrombi, emboli, and corticosteroids. Growing bones of children and adolescents are often affected, and in most instances, the cause of such infarctions is not evident. Legg-Calve-Perthes disease refers to osteonecrosis in the femoral head in children. Collapse of the femoral head may lead to joint incongruity and severe osteoarthritis. Chondroma (choice B) is a benign, intraosseous tumor composed of well-differentiated hyaline cartilage. Fibrous dysplasia (choice C) is a developmental abnormality of the skeleton, characterized by a disorganized mixture of fibrous and osseous elements in the interior of the affected bones. Osteitis fibrosa cystica (choice D) occurs in primary hyperparathyroidism.Diagnosis: Avascular osteonecrosis