Cortisone injections will not heal tennis elbow. I know because I am a tennis coach and I had tennis elbow.
Tendonitis is an inflammatory response. It is like inflammation anywhere in the body. It is like arthritis, inflamed blood, inflamed arteries, inflamed digestive tract and anything else. Inflammation is a response to cells that are not getting: water, oxygen, nutrition, or purging of toxins.
Cortisone is a hormone that covers up this response. It does not solve the problem that the body is responding to. Also, cortisone activates the sympathetic nervous system which is your fight or flight nervous system which makes it even hard to heal and to nutrify the body. This leads to more inflammation both macro and micro inflammation.
In order to heal you must activate the parasympathetic nervous system. This is your rest and heal response. The body must be able to rest and heal to recover from damage or injury. Cortisone actually works against you.
If you are an athlete like me you are in an especially dangerous situation because your body is losing valuable fluids and nutrition in the sweat. In my case I had a stroke in 2010 because I was not drinking enough water and I was not absorbing the valuable nutrition to replace the ones I lost in my sweat.
Tendonitis is a sign that you are not absorbing your nutrition. This may be because you are eating the wrong foods and / or your digestive tract has been compromised. You also must supplement your diet with the 90+nutrients available from Youngevity.
If you need more information just ask. But no Cortisone shots will not help in my opinion.