Desperately anxious, pointing cryptically to knee? (3,4)

I believe the answer is:

mad keen

'desperately anxious' is the definition.

'pointing cryptically to knee?' is the wordplay.
'pointing' becomes 'mad' (I can't explain this - if you can you should believe this answer much more).
'cryptically' indicates anagramming the letters.
'knee' anagrammed gives 'keen'.
'mad'+'keen'='MAD KEEN'

(Another definition for mad keen that I've seen is " Very eager".)

I've seen this clue in The Guardian.

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