Injury as limb at first sound twisted (6)
I believe the answer is:
lesion
'injury' is the definition.
(I know that lesion is a type of injury)
'limb at first sound twisted' is the wordplay.
'at first' suggests taking the first letters.
'sound' becomes 'noise' (a noise is a sound).
'twisted' shows that the letters should be reversed in order.
The first letter of 'limb' is 'l'.
'noise' written backwards gives 'esion'.
'l'+'esion'='LESION'
'as' acts as a link.
(Other definitions for lesion that I've seen before include "A cut or wound in insole" , "Harmful change in bodily tissue as from injury" , "Kind of injury in insole" , "Damaged area of tissue" , "Damage to tissue from injury or disease" .)