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
Deformity is most commonly seen in primary osteoarthritis of the knee joint - 
Select and explain. 
A. Genu valgum, B. Germ recurratum, C. Genu varus, D. Procurvaturn.
C: Genu varus
Answer: C: Genu varus 
Explanation: In knee joint osteoarthritis, medial joint space is affected earliest and causes asymmetrical joint space narrowing. This results in varus deformity (genu varus).