I'm a physical therapist (and tennis player) with 20 years of experience in the sports medicine setting. At my age, I also have plenty of first-hand experience dealing with some of the aches and pains associated with our game. In my own profession, there is still some confusion on what is going on with tendon injuries, and l would like to take this opportunity to share what I have learned so that you all will better understand your own injuries and can take an informed stance when you are trying to help yourself.
Inflammation of a tendon (tendinitis) can occur following an acute injury, which might even involve localized micro-tearing. In these cases, rest, bracing, ice, and medication helps, then you slowly get back to your prior training levels. Sometimes, that's the end of the story. Sometimes, however, it goes away for awhile, then the pain comes back. It is in these cases where we think a degeneratvie process is going on (tendinosis). Following the original injury, the body tries to heal itself, but it does so in an inferior manner. The resulting repair or scar is not as strong as a normal, healthy tendon would be. This makes future injuries more likely. Imaging shows that you can get pockets of "fresh" inflammation, but the primary problem is degenerative. That's why anti-inflammatory treatments can help, but not always permanently.
There's another change that occurs with degenerative tendinopathies: the blood vessels are different. They are weaker, disorganized, and really don't do a good job bringing blood products to the interior portions of the tendons. That's another reason why degenerative tendons don't heal so well.
So, basically, with most tendon problems, to get it better, one needs to manage the dysfunctional scar tissue, get healing blood products to the deep portions of the tendon, appropriately re-model the newly healed structures into something that is strong and functional, and deal with any racket, form or strength issues. Some doctors are trying to accomplish the first two goals with techniques like PRP injections. In my practice, I perform a technique called ASTYM, which is designed to stimulate a healing response in these degenerated tendons, and has a documented success rate of 89.8% with tennis elbow.
For those of you who are still awake, I hope this information sheds some light on some of these stubborn problems like tennis elbow; why they come and go for no known reason, and why they can be so difficult to get over.