What a sudden pain in the shoulder could mean

Tennis players with a hard serve are prone to getting rotator cuff injuries. — Filepic

Our rotator cuff is a large group of muscles and tendons that surround and protect our shoulder joint. There are four muscles altogether.

You see, our shoulder joint is made out of the head of our upper arm bone (humerus) inserted into a shallow cavity (the glenoid cavity) in our shoulder bone (scapula).