Doctor has pie prepared as medical speciality (12)
I believe the answer is:
Here is my best explanation:
'medical speciality' is the definition.
The definition suggests a singular noun which matches the answer.
'doctor has pie prepared' is the wordplay.
'prepared' is an anagram indicator.
'doctorhaspie' with letters rearranged gives 'ORTHOPAEDICS'.
'as' acts as a link.
(Other definitions for orthopaedics that I've seen before include "The treatment of bone and muscle disorders" and "Field to operate".)