While there were was an account from the book "City Of God" in the 5th century about a person being forced into a nail-studded box as a form of torture, and a similar account by Polybius in 100 BC, these accounts are suspect at best. There's little to no evidence that Iron Maidens were used in the early-late medieval period at all.

"The first historical reference to the iron maiden came long after the Middle Ages, in the late 1700s. German philosopher Johann Philipp Siebenkees wrote about the alleged execution of a coin-forger in 1515 by an iron maiden in the city of Nuremberg. Around that time, iron maidens started popping up in museums around Europe and the United States. These included the Iron Maiden of Nuremberg, probably the most famous, which was built in the early 1800s and destroyed in an Allied bombing in 1944.   " From this article from Live Science

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The only concrete uses of the iron maiden we have records of are from the Hussein Family using them to torture people (The above article has a paragraph on the bottom about that as well). That, and as stage props at Iron Maiden concerts.

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