MRI is a special diagnostic study that uses strong magnetic fields to visualize bony and soft tissue structures. MRI creates images of bone, muscle, tendons, ligaments and all other soft tissues.

The meniscus is a disc of tissue between the ends of two bones that form a joint. In the shoulder, it's found between the end of the collarbone (clavicle) and the edge of the shoulder blade (acromion.)

Muscles are tissues composed of fibers that contract, allowing body parts to move. One of the most important shoulder muscles is the supraspinatus muscle — one of four rotator cuff muscles.