Sorry for your trouble. They do not do a standard MRI on any metal joint. They have a modified procedure. Check with your physician on what his care plan will be. Stiffening up is not a good answer. Interferential Electrical Current with heat and and some deep massage will help.along with contact, relax,stretch and repeat and recombant bike for 5-ten minutes to tolerance. It is old fashion, but it is comfortable and pain relieving.(Cross he knee with a modulated surge.) If they won't do it, go some place that will.