Made up first-class piece in bone (5)
I believe the answer is:
tibia
'bone' is the definition.
(I know that tibia is a bone)
'made up first-class piece' is the wordplay.
'made up' is a reversal indicator (in a down clue, letters go up).
'first class' becomes 'ai' (Ab - top quality).
'piece' becomes 'bit' (bit is a kind of piece).
'ai'+'bit'='aibit'
'aibit' in reverse letter order is 'TIBIA'.
'in' is the link.
(Other definitions for tibia that I've seen before include "Bone of the lower leg" , "Part of leg of" , "Bone in osso bucco" , "ancient pipe" , "The large shinbone" .)