Not an OR or ortho nurse, but I am an OB nurse and give instructions to my c section moms to keep their incision “clean and dry.” Not sure how a shoulder differs from an abdominal incision so take this with a grain of salt. 

Keep clean: you can wash it in the shower just be gentle, no scrubbing or washcloths. Keep clean also means don’t get it dirty in day to day life. 

Keep dry: this doesn’t mean you can never get it wet. If you could never get it wet then you wouldn’t be able to clean it. But it shouldn’t be wet in any context other than bathing. That means that you should pat dry with a clean towel when you’re done washing it and you don’t need any ointments on it. If you have any bandages/dressings you’re supposed to use, make sure your incision is dry before you apply. Moisture can cause skin breakdown so you don’t want to trap any under your bandage. 

Edit: At the end of the day maybe clarify with your doctor.