Characteristics of KBD pateients. A. Representative patient with grade III KBD (male patient, age 55 years), showing retarded growth of the two knees. B and C. Radiographic images of the left knee of a patient with grade II KBD (male patient, age 48 years), (B) anteroposterior and (C) lateral directions, showing an enlarged joint space and obvious joint space narrowing. D Hematoxylin-eosin staining of adult control articular cartilage (50 y, male), and E Hematoxylin-eosin staining of KBD articular cartilage with chondrocyte clusters in the eroded surface, necrotic chondrocytes and fibrous cartilage in the middle and deep layer of knee joint (55 y, male). (D and E, 40 ×).