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
All of the following show genu recurvatum, except 
Select and explain. 
A. Perthe's disease, B. Rheumatoid arthritis, C. Poliomyelitis, D. Rickets
A: Perthe's disease
Answer: A: Perthe's disease 
Explanation: None