Observational research was conducted by HR Brenner in 2003.
The research looked at how often olfactory issues come up after nasal or paranasal sinus surgery. The 6 month study of 184 subjects gave pre and post assessments that involved a subjective questionnaire and an objective smell test.
The results show that no patients developed anosmia (complete loss of smell) while about 3% developed an awareness of some type of loss of smell.
Not much, unless you’re one of the 3 in 100.