Xray and MRI showing different diagnosis

I had L5-S1 fusion 2010; for over 1.5 years sciatic pain without relief with RFA. I had an x-ray which showed, Prior lumbosacral fusion procedure with new osteolysis of the anterior margin of the S1 vertebral segment around the inferior aspect of the anteriorly placed screw, raising possibility of pseudoarthrosis or infection. But MRI "normal". Which do you believe? I see surgeon soon but terrible pain started in right leg and now going down left leg.