Intra-articular loose body caused by avascular necrosis of the femoral head in children.

In children, avascular necrosis of the femoral head occurs easily because of the difference in the domination of blood flow compared with that in adults. Here we report a rare case of a 12-year-old girl who sustained a femoral neck fracture. The femoral head collapsed after open reduction and internal fixation. The hip developed into subluxation because of the gradually enlarged loose body in association with avascular necrosis. These results might be explained by the fact that blood circulation from the ligamentum teres temporarily increases during the ages of 8-12 years.