Metal disk in hindquarters

Idle curiosity question. A few years back friend groomed a tb at the track who had a flat metal disk about the size of your palm under the skin, above the muscles on the side of his hind quarters just below the hip bone. He was imported from Ireland and had raced there a year before coming over. He was sound and racing well but no one knew why he had it - any ideas?

Can you ask the folks from Ireland where he was imported from?

this was a horse from a few years ago and he was a claimer so had changed hands a few times, it came up in conversation about “odd things you see in horses” while we were trimming hooves, so unlikely to track down his importers, thought I’d ask on here out of idle curiosity as this forum has a lot of horse people who’ve seen their own “odd things”

Do you know it was metal because the area had been radiographed? Or did it just feel that way?

There’d really be no purpose to putting a plate under the skin and over the muscle layer. Maybe it was an odd scar of the muscle layer that felt hard? Or maybe it was inserted for nefarious purposes, and was intended to be removed once he was stateside (some sort of smuggling effort…?)