First, what is cortisone? Actually, cortisone is just one of many medications in a group called corticosteroids. Other corticosteroids include prednisone, prednisolone, methyprednisolone (medrol), and dexamethasone. Most people just say cortisone to mean any of these medications. Cortisone and the other corticosteroid medications work by decreasing the body's immune response--it is an anti-inflammatory. Inflammation is the immune system flaring out of control and causing pain.
Is cortisone just a "temporary fix"? For many people, a single cortisone shot is an effective, permanent solution to an inflammation problem. If inflammation is like a fire, then cortisone is the water to put the fire out. Sometimes the fire, or inflammation, is completely eliminated by the cortisone. Sometimes, though, inflammation remains, and can flare back up. For some people, the cortisone shot doesn't put out the fire completely and they have pain and inflammation come back. And for some people, the injection doesn't work at all.
Doesn't cortisone damage the tendons and ligaments in my shoulder? There may be a very small effect on the tendons in the shoulder. However, a single injection is absolutely safe and causes no weakening. With multiple injections, however, there is a risk of weakening tendons in the joint. If multiple injections might be necessary, then you should know about this small but real risk.
Are there any other side effects of cortisone? In patients with diabetes, cortisone may cause a temporary increase in blood sugars. This effect wears off after a week or so. There is a small increased risk of infection after a cortisone shot, because the shot decreases the body's ability to fight infection.
How is the injection given? In my practice, I use a small ultrasound machine to guide the injection into the correct location. Here is a video of a cortisone injection: