To me, "surgery" is uncountable, and I would only say "perform surgery". It's sort of the abstract "art" of a surgeon. A bit like how I might "create art", but if I draw a picture, I wouldn't say that I "have created an art".
However, some people seem to use "surgery" the way I would use "operation" and say not (only) "I had surgery" but "I had a surgery", in which case the indefinite article "a" would be possible.
I'll check the sentence and add an alternative with "a surgery" if it's not already there.