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
The most common site of primary osteoarthrosis is - 
Select and explain. 
A. Hip joint, B. Knee joint, C. Ankle joint, D. Shoulder joint
B: Knee joint
Answer: B: Knee joint 
Explanation: In general, weight bearing lower limb joints are affected more commonly than upper limb joints.
However, No textbook has mentioned which is the commonest joint : knee or hip.
According to me it is knee because of following facts :-


I have seen hardly one or two cases of primary OA of hip; while, I have seen hundreds of cases of Primary OA of knee in my OPD. At least 4 to 5 patients of primary OA of knee comes daily to my OPD.
"OA commonly affects the knee joint"   —Ebnezar
"OA of hip is second in frequency to the knee joint" —Ebnezar