You can distinctively tell a screw on x-ray or MRI films. If you can't tell it's a screw, it's not a screw. Every screw I've seen clearly has threads in them. although they could use tinier ones than I've seen on lots and lots of MRI films, you can distinguish it's a screw.

I have seen an x-ray where a woman had been shot in the abdomen with a shotgun and we could see the bee-bees in her belly, all over her belly. Metal shows up clear/void space outlining metal things/light blue area.

Shiny would be a little different. not seen "shiny." not heard anything described as "shiny" on x-rays or MRIs. It could something either from the epidurals - long shot... they may have left some hardware in there - or it's congenital or a disease process not identified for you yet. it's something even if it turns out to be not harmful or threatening, maybe some kind of deposit your body can't get rid of. If the radiologist read the MRI as "plates and screws," he's the expert, the one that's supposed to know. They're not wrong too often. and if the ER doctor came back and asked - probably because you didn't declare back surgery in a history - they're puzzled too.

how about when you were born or too young to remember? can you find out from parents or family if they did do any procedures or if you were just hospitalized for something.

Have you ever been in accidents of any kind and went for treatment, unconscious maybe.

Proceed with caution.