Iodine injected in rather twisted part of leg (5)
I believe the answer is:
tibia
'part of leg' is the definition.
(bone of the leg)
'iodine injected in rather twisted' is the wordplay.
'iodine' becomes 'I' (chemical symbol).
'injected in' is an insertion indicator.
'rather' becomes 'a bit' ('a bit' can mean rather or to some extent).
'twisted' shows that the letters should be reversed in order.
'i' put within 'abit' is 'aibit'.
'aibit' written backwards gives 'TIBIA'.
(Other definitions for tibia that I've seen before include "Shin bone" , "part of skeleton" , "Bone of the lower leg" , "ancient pipe" , "The large shinbone" .)