Somewhat upset about iodine in bone (5)
I believe the answer is:
tibia
'bone' is the definition.
(tibia is a kind of bone)
'somewhat upset about iodine' is the wordplay.
'somewhat' becomes 'a bit' (a bit).
'upset' says the letters should be written backwards.
'about' is an insertion indicator.
'iodine' becomes 'I' (I is the chemical symbol for iodine).
'abit' reversed gives 'tiba'.
'tiba' enclosing 'i' is 'TIBIA'.
'in' acts as a link.
(Other definitions for tibia that I've seen before include "part of skeleton" , "The large shinbone" , "ancient pipe" , "Part of leg of" , "Bone in osso bucco" .)