How to analyze the change in incidence over time?


I am studying the change in incidence of a specific type of surgery over time. I have 1 independent variable which is YEAR (continuous), and one dependent variable (rate of surgery/incidence per 100,000 population). There is a downward trend observed, but I would like to analyze it statistically.

What statistical test should I choose? And, how should I run it in SPSS?