ktr,
What actually generates the pain from spinal conditions is still not very well understood. The nerves which innervate the region around the hip come from the upper lumbar nerve roots.
Disc bulges are very common. They can be anything from being normal to the early signs of degeneration of the disc. The annulus is the tough cartilage ring on the outside of the disc complex. Disc bulges have been noted in up to 60% of people with back pain, who have had an MRI done for other reasons. So, though they are often listed as a source of back pain, their finding has to really be correlated with a patient's history and physical exam.
Now, at the L4-5 disc, some of the nucleus pulposus, the jelly like material in the center of the disc complex, has extruded (squirted out) and is now in contact with the sac that surrounds the spinal cord. You have to remember that the spinal cord itself ends at the level of the first lumbar vertebra. At the level of the L4-5 disc, the sac contains cerebrospinal fluid and the nerve roots, which are floating within the fluid. That is why a lumbar puncture can be done at this level without worrying about hitting the actual cord. So a disc fragment compressing the sac here is usually not too much of a problem. A midline extrusion does not affect the exiting nerve roots.
So, in general the findings on this MRI would probably not cause significant pain in the true hip joint (pain from the true hip joint, which be located in the anterior groin region, usually deep in nature).
You should discuss the findings of the study with the surgeon who ordered it. He/she knows your history and has examined you.
Good luck.