What happens when a mri says that i have a meniscus displacement and the doctor says i don't who is right? how accurate is the mri ?

Hard to say: The MRI is about 95% accurate on the medial meniscus and about 90 % on the lateral side. However not all meniscal tears should have surgery, small tears where the symptoms don' t match the MRI and meniscal tears in a knee with significant artritis are two examples where the clinical picture may be more important than the test results. Hope that helps!