It sounds like the TSO in question was slavishly following the SOP on this one -- which, as we all know, leaves a lot to be desired.

The SOP states that we are not supposed to order a passenger to remove a medical or assistive device, nor are we supposed to accept their offer to voluntarily remove said device. Obviously, this policy was devised by a liability-conscious person who did not want the bad press/lawsuits resulting from people falling, etc.

However, if played out strictly to the letter, it creates a weird sort of "don't ask, don't tell" scenario in which we're not required to STOP a passenger who is removing their brace (etc.), but if they ASK us if they can/should remove it, our proper response should be to decline, and send them for additional screening instead.

Which results in the sort of hassle you endured. Sorry about that!