Work schedule is revolutionary inside sanatoriums (4)
I believe the answer is:
Here is my best explanation:
'work schedule' is the definition.
(I've seen this before)
'revolutionary inside sanatoriums' is the subsidiary indication.
'revolutionary' says the letters should be written in reverse.
'inside' indicates a hidden word.
'ator' is hidden within 'sanatoriums'.
'ator' back-to-front is 'rota'.
'is' is the link.
(Other definitions for rota that I've seen before include "List of duties to be done, or people to do them", "Cycle of duty", "Duty schedule", "Duty roster", "list of duties", "List of people to do job in turns", "Work schedule", "Working times list", "Schedule" and "Duty list".)