Overcome by strong emotion, like a person with osteoarthritis might be? (4,2,3,5)
I believe the answer is:
weak at the knees
'strong emotion like a person with osteoarthritis might be?' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'overcome by' is the wordplay.
I cannot really understand how this works, but
'overcome' could be 'weak' (similar in meaning) and 'weak' is found within the answer.
'by' could be 'at' and 'at' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for weak at the knees that I've seen before include "Housemaid said to be so helplessly" , "emotional?" , "Wobbly" , "Emotionally overcome" .)