Very, very badly sore behind knee, ultimately (4,2)
I believe the answer is:
ever so
'very' is the definition.
(I've seen this before)
'very badly sore behind knee ultimately' is the wordplay.
'very' becomes 'v' (abbreviation).
'badly' indicates anagramming the letters.
'behind' is a charade indicator (letters next to each other).
'ultimately' suggests the final letters.
The final letter of 'knee' is 'e'.
'sore' is an anagram of 'erso'.
'v'+'erso'='verso'
'verso' after 'e' is 'EVER SO'.
(Other definitions for ever so that I've seen before include "Very much" , "really" , "Extremely" , "To a very great extent" , "Greatly" .)