Final answer:
Swimmer's shoulder is a common form of tendonitis resulting from the repetitive use of the shoulder in racquet sports like tennis, leading to microtrauma, inflammation, and in severe cases, the need for surgical repair.
Step-by-step explanation:
The type of tendonitis that is very common with overuse of the shoulder in flexion from sports such as tennis or racquetball is often referred to as swimmer's shoulder. This condition is a form of tendinitis that arises due to repetitive motion and overuse of the joint, resulting in microtrauma and an inflammatory response. This is especially true in racquet sports where the constant extension and flexion of the arm creates large forces at work on the shoulder tendons. In severe cases of tendinitis, the tendon can tear loose, requiring surgical repair which can be painful due to the slow healing nature of connective tissue in the tendon.