We've all heard of tennis elbow, or golf elbow - pain in these areas caused by tendonitis. But tendonitis can also cause pain in many areas of the hand and arms. Tendonitis is a result of swelling of the tendons. Tendons are rope-like structures which connect the muscles in our body to the bones which they have to move. There are many tendons in the hand and forearm that, when irritated and swollen, are painful.