1. 75-90% of patients present in the long bones; 2. 84-99% of lesions invade 1 cm into the subchondral bone of the articular surface; 3. distal femur: 23-30%; 4. proximal tibia: 20-25%; 5. distal radius: 10-12%; 6. sacrum: 4-9%; 7. proximal humerus: 4-8%; 8. proximal femur: 4%; 9. hip: 3%; 10. vertebral body: 3-6%; 11. wrist bone: 1-5%; 12. foot bone: 1-2%; 13. patella and trochanteric process of the femur may also occur.