Back surgery transformed Marianne Barker? (10)
I believe the answer is:
pomeranian
'barker?' is the definition.
(I've seen this before)
'back surgery transformed marianne' is the wordplay.
'back' says the letters should be written in reverse.
'surgery' becomes 'op' (short for operation).
'transformed' is an anagram indicator.
'op' back-to-front is 'po'.
'marianne' anagrammed gives 'meranian'.
'po'+'meranian'='POMERANIAN'
(Other definitions for pomeranian that I've seen before include "Dog akin to spitz" , "one with a tendency to yap" , "Dog (from Poland or Germany?)" , "Bismarck wanted to save his bones" , "Polish dog breed" .)