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
Injury to the medial meniscus is rather impossible when the knee joint does not - 
Select and explain. 
A. Extend, B. Flex, C. Rotate, D. Abduct adduct
B: Flex
Answer: B: Flex 
Explanation: Some guides have given option 'c' (rotation) as the answer. But their answer is wrong.
Yes; medial meniscus injury occurs due to rotational (twisting) injury, but the rotation is possible only in the flexed knee.
It has already been explained that in the extended position of the knee, knee gets locked and rotation is not possible. Therefore, meniscal injury cannot be possible in the extended position.
In flexed position, knee gets unlocked and rotation can occur in a flexed position. Therefore, meniscal injury occurs in a flexed position.

"The twisting movement, an important component of the mechanism of injury, is possible only with a flexed knee". - Maheshwari

So, the meniscal injury is not possible if the knee cannot be flexed.