I have a fusion at l4-l5 with instramentation. an mri in 2010 confirmed i had a bulging disc at s1 where i have pain. a new mri & cat scan was ordere?

Consult your Spine: Surgeon. It is a common to have increased stress at the spinal segment above and below a fusion, with resultant acceleration of degeneration of these segments. However because you see these on xray/mri doesn't mean it is causing any symptoms. A well-trained spine specialist in your area will help you identify the pain generator, which might have nothing to do with the bulging disc you described.