Leg bone slightly twisted going round island (5)
I believe the answer is:
tibia
'leg bone' is the definition.
(tibia is a kind of leg bone)
'slightly twisted going round island' is the wordplay.
'slightly' becomes 'abit' (I've seen this before).
'twisted' says the letters should be written backwards.
'going round' is an insertion indicator.
'island' becomes 'i'.
'abit' backwards is 'tiba'.
'tiba' enclosing 'i' is 'TIBIA'.
(Other definitions for tibia that I've seen before include "Part of leg of" , "The large shinbone" , "Bone in osso bucco" , "ancient pipe" , "Shin bone" .)