Inflammation: skill with this involved bringing in bits of remedial intervention (9)
I believe the answer is:
arthritis
'inflammation' is the definition.
(I have seen 'Inflammation of joints' mean 'arthritis' so perhaps 'inflammation' could also mean 'arthritis')
'skill with this involved bringing in bits of remedial intervention' is the wordplay.
'skill' becomes 'art' (both can mean a talent).
'with' says to put letters next to each other.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'bringing in' is an insertion indicator.
'bits of' indicates taking the first letters.
The initial letters of 'remedial intervention' is 'ri'.
'this' anagrammed gives 'htis'.
'htis' placed around 'ri' is 'hritis'.
'art'+'hritis'='ARTHRITIS'
(Other definitions for arthritis that I've seen before include "Inflammation of joints" , "complaint" , "Joint pain" , "Inflammatory disease of the joints" .)