Rotary cuff injury or possible ac joint separation. what's the difference?

These are 2 differen: Conditions, like a tooth problem and a gum problem. The ac joint separation is the result of an injury to the joint on top of the shoulder; while the rc injury is a tear of the tendons (which from the rc). They are like 1/2 an inch from each other. The ac injury would be obvious on the xrays while rc injury is mostly seen on mri.