Can I get subcision after fillers?

I have one depressed scar from a skin lesion excision. I have had dermal fillers (Restylane/Perlane) placed under the scar. Intially, there were good results, then the scar came back like I never had the treatment. I was wondering, how deep does a scar have to be before you can have subcision? Can a subcision be performed after fillers have been injected into a depressed scar? I don't mean straight away, like, give it a month.