Healthcare providers are, because of the beloved lawyers (you win, I win; you lose, I win), punitive damages and mischievous litigants, absolutely paranoid about exposing patients to avoidable risk. Unfortunately, the legal environment of some countries makes this attitude necessary for self-preservation. Please therefore allow me to remain anonymous: I'm a recently retired radiologist member of this forum. (And, in case you were wondering, I never had any case brought against me, thank goodness!)
The two risks from embedded metal in MRI are heating (due to eddy currents) and displacement due to the huge magnetic fields. In a simple bit of the body, with little in the way of sensitive clockwork, and strong structural tissues, displacement realistically isn't a risk. The heating effect, on a small lump, is likewise neglegible. Plenty of people get scanned intentionally, who are known to have metal structures within them. For practical purposes, as long as the metal is known to be "MRI-friendly", ie not ferro-magnetic, it's safe. This goes for aneurysm clips in the brain, and not just for those within politicians!
There was a paper, some years ago, addressing the risks to attending personnel, etc, in the vicinity of MRI scanners. It was advised that firearms should not be taken into the scanning room! (Yes, it was an American paper!). If I remember correctly, there was one incident where a handgun was caused to discharge as a result of the magnetic field.