In 1887, König claimed that loose bodies in the knee joints of young persons had three causes: (1) very severe trauma; (2) lesser trauma causing contusion and necrosis; and (3) minimal trauma acting on an underlying lesion-for which he suggested the name osteochondritis dissecans. His thesis has stood the test of time. We still confuse the second and third categories but osteochondritis dissecans has been identified as an ossification defect.