Does sacroiliitis show up on xray or mri?

Yes, it can... May depend on just how long you've been having the pain... Physical exam is probably the best way to make the diagnosis... A fair screening test is to lie on your side on a firtm surface and have someone smash down [heavily] on your hip... or lie on your back, place one leg over the other [like crossing your legs] and have someone press down on your knee... this will put stress on the SI joint on that side of your body, resulting in a lot of pain [that's IF you have sacroiliitis on that side of your hip]...