Twisting of antlers or of breastbone (7)
I believe the answer is:
sternal
'of breastbone' is the definition.
(I've seen this before)
'twisting of antlers' is the wordplay.
'antlers' can be anagrammed to 'STERNAL'.
But, I'm unsure how the anagram is indicated.
'or' is the link.
Can you help me to learn more?
(Other definitions for sternal that I've seen before include "of breastbone" , "of chest" .)