Why is Dislocation Often a Cause of Shoulder Pain? 

The positioning of your upper arm bone (humerus) and the socket (glenoid) in your shoulder blade lets you rotate your arm in a wide arc. A network of muscles and tendons called the rotator cuff overlays the shoulder joint to keep the bones in place. 

Dislocation is often a problem in the shoulder more than other joints, and these types of injuries often damage the rotator cuff as well. As the head of the humerus comes out of the glenoid, it can also cause the labrum (cartilage that lines the rim of your glenoid) to tear. 

A torn glenoid is called a Bankart lesion. A similar injury is a SLAP (superior labrum anterior and posterior) tear, which affects the top part of your labrum at the attachment point of your biceps tendon. 

If you dislocate your shoulder once, you’re more likely to do it again, and injuries like Bankart lesions can lead to chronic shoulder instability.