My mother was 82 when they did hers and it worked wonders! For over 20 years she had suffered from a torn ligament, destroyed cartilage, and a cracked kneecap that liked to play the "Now I'm open. Now, I'm closed." game.
She tried the synovial fluid knee injections, but she kept having to repeat them until it finally stopped helping at all. Apparently if the fluid from your own body drained away, so will the injected fluid over time. As time goes on, the fluid drains more quickly and must be repeated with less time in-between injections.
The steroid injections also helped a little while, but we learned that was putting a bandage on gaping wound, so to speak. The side effects from continued use played havoc with her entire system and also slowly stopped working. One of the worst side effects is not known publicly and it should be. If you have knee, elbow or jaw injuries before a cortisone shot, it will erode the bone over time and make it much worse. That information can easily be found on medical sites about cortisone shots and from your pharmacist paperwork on cortisone from the companies that make it.
She has severe diabetes so she was afraid she would never heal and kept putting it off. When her knee was completely gone, she had no choice and it was done. Within three days she was up and walking and within a few weeks it was healed.
She says it is well worth the trouble and if you are in pain and cannot hold a normal life because of that pain, go for it. The option of staying down is just not worth it.