Initially surgeons cannot operate until really clean (5)
I believe the answer is:
scour
'clean' is the definition.
(thesaurus)
'initially surgeons cannot operate until really' is the wordplay.
'initially' indicates taking the first letters.
The initial letters of 'surgeons cannot operate until really' is 'SCOUR'.
(Other definitions for scour that I've seen before include "Full" , "Look high and low" , "Turn upside down" , "Scrub hard" , "Rub with a gritty substance" .)