This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
Osteonecrosis of femoral head seen in -a) Sickle cell diseaseb) Gaucher's diseasec) Polycythemiad) Hyperparathyroidisme) Fracture 
Select and explain. 
A. bcde, B. abcd, C. acde, D. abce
D: abce
Answer: D: abce 
Explanation: Sickle cell anemia and polycythemia can cause AVN.