@ropnrose

"My rheumatologist has determined that I have osteoarthritis. I informed him that I never had these aches before PMR/GCA. He said osteoarthritis doesn't usually 'show up'. I asked if my Prednisone usage damaged my joints and he said it possibly did."
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Just my opinion because I don't really know. I think we all have some osteoarthritis at the age we are diagnosed with PMR whether we feel the pain or not ... I certainly did.

I had very severe osteoarthritis in my right knee from a sports injury during high school. I was told that I needed a knee replacement before the age of 30 but I had to wait until I was 60.

My right knee was already deranged but the mystery was how bad my left knee was when it was replaced. I actually had my "good" left knee replaced before my "bad" right knee. Both surgeries were done during the height of my PMR diagnoses when I was still taking 30 mg of Prednisone. My orthopedic surgeon basically said the same thing as your rheumatologist. He said both my knees were so bad that "wear and tear" arthritis couldn't explain it all. I knew how bad my right knee was but I always called my left knee my good knee. My orthopedic surgeon said chronic inflammation would explain it but Prednisone didn't help the situation because of how it destroys connective tissues.

Artificial intelligence seems to agree:

"The Prednisone Paradox: While high-dose Prednisone is critical for knocking down the systemic inflammation of PMR, it comes at a cost to your musculoskeletal system. Glucocorticoids are known to inhibit collagen synthesis and weaken connective tissues, accelerating structural damage in joints that are already under stress."
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Both my knees had severe osteoarthritis in addition to severe osteoarthritis of my spine and everywhere else they look since I tapered off prednisone. Having that much arthritis might only be explained by wear and tear AND chronic inflammation AND prednisone.