Tendon that's twisted is not used (5)
I believe the answer is:
sinew
'tendon' is the definition.
(I know that tendon can be written as sinew)
'twisted is not used' is the wordplay.
'twisted' says the letters should be written in reverse.
'not used' becomes 'new' (I've seen this in another clue).
'is' written backwards gives 'si'.
'si'+'new'='SINEW'
'that's' is the link.
(Other definitions for sinew that I've seen before include "source of physical strength" , "Tendon, for example" , "Force" , "Cord of tissue connecting muscle to bone" , "Tough material" .)