Over time, strained tendons become thickened, bumpy, and irregular. Without rest and time for the tissue to heal, strained tendons can become permanently weakened. Damaged tendons can occur on either side of the elbow. When it happens on the outside of the elbow, which is most common, it is called tennis elbow. No one knows exactly what causes the pain of tennis elbow.
Most experts believe it is due to the small tears that develop in the tendons.
Other possible causes include the development of scar-like tissue under the tendon, wear and tear of the elbow joint, or irritation and inflammation of nerves that pass near the elbow region. The development of tennis elbow often relates to the way that workers carry out activities such as gripping, twisting, reaching, and moving. Tennis elbow is associated with jobs that require repeated or forceful movements of the fingers, wrist, and forearm. It can develop because of too much force at once or small amounts of force for too long a period. Tennis elbow can cause extreme tenderness on the outer side of the elbow.