Had a cortisone shot for shoulder pain and now 10 days late. is it possible cortisone shot caused missed period?

Cortisone shot: Usually not, especially if they injected the shot directly into the shoulder joint itself. If that is the case then the shoulder joint itself is encapsulated and the steroid stays right in the joint space. I would take a pregnancy test. Make sure and doing first thing in the morning as it is a more accurate test than later in the day. Good luck.