This is an ironic question for me as I recently went to my doctor to discuss some emergency room results. One of them included my spine, they call it musculoskeletal.. I've had a long time history with arthritis. And actually believe I got the PSA before I got psoriasis.
It's a catch 22 it makes it milder on the skin but very hard on the spine and other joints.
My primary doctor told me we all have some degenerated or weakend discs as we age. But they are also aware that I have arthritis. Which doesn't help. My parents both had diagnosed forms of arthritis it was unavoidable if you think about it. Ironically and getting family history recently I'm not told any of my siblings have arthritis. They have other issues but maybe it's just not presented in findings? I know I have it and it's diagnosed.

As for PSA itself yes it is very demanding on the bones. I can only say that from experience. But for psoriasis which is mostly skin and probably other tissue and organs I don't think it's a cause directly of it. As the article says above it doesn't mention psoriasis itself. It probably adds to it but I don't believe it would cause that to be. It's likely some other reason. Our body is so complicated it doesn't have just one thing sometimes to deal with. My doctor in summary basically felt and expressed it can largely happen due to injury where a spine could be fractured or damaged as a result of.

Hope you have a good week ahead