Prednisone can make you feel better whether you have RA or OA. It's a general purpose inflammation reducer used in a wide variety of diseases. It can be injected directly into a joint to ease pain and swelling, given in an intramuscular injection or taken orally to quiet an overall RA flare-up, inhaled to help asthma and COPD patients breathe better, and more. My mom takes injections in her lower back to temporarily ease pain. My guess is you have a low back injury that is irritating the sciatic nerve, which travels down the back of your hip and down your leg. Bone deposits can build up due to altered mechanics in how your walk, sit, stand, etc. after an injury. The old song, "the hip bone's connected to the knee bone" has more than a little truth to it! A foot injury, for example, makes you limp. This puts stress on the adjacent joints, so eventually your knees, hips and back start to hurt, too. This is why the goal of physical and occupational therapy is to get you back to normal, even function - to prevent further problems down the road.
When I had my first hip replacement, it made my leg a good 1-1/2 inches longer than the other one. Over the three years before I had the other hip replaced, I developed problems in my left foot, opposite knee, and lower back.
Having said that, RA can have many different triggers. A common infection can trigger the immune system to start attacking the body - no one knows why. Stress or an injury, basically anything that prompts an immune system response can potentially trigger RA or another autoimmune disease. It can run in families, or appear apparently out of nowhere. My guess is you do NOT have RA and likely won't develop it, but your doctor may be testing you just to be safe.
Look up the common initial symptoms of RA on a site such as here on medhelp.org
or arthritis.org. I think you'll find it eases your mind...or it may spark a conversation with your doctor that can lead to early treatment!
It's important not to rely on prednisone for the long-term - the long term side effects are not pretty. IMO only it's better to sumbit to surgery to fix the problem as well as it can be fixed, but that's a personal decision. :)