1. At the L5/S1 segment, there is moderate disc degeneration with central broad-based disc herniation and inner annular tear but without associated stenosis or neural compression.
2. At L4-5, L3-4 and L2-3 segments, there is moderate disc degeneration.
3. Lumbar form of Scheuemann's
Would this explain all my SI joint instability? My PT told me that they may have to fuse my L5/S1? Am I up the creek???????
This doesn't really clarify anything. The information is so general as to not be very helpful. You have a general idea of what's going on, but it doesn't indicate much detail.
It could explain if you are having radiating pain in your leg or legs or in your lower lumbar spine but it doesn't indicate anything about SI joint pain. For that you would need specific imaging for the pelvic area, being sure they included the sacrum and ilium.
Apparently your surgeon thinks the disc degeneration is sufficiently bad that he doesn't think a discectomy at L5-S1 would resolve your pain....but that would be a question to ask him, since you have a broad-based disc herniation and an annular tear at the disc between L5 and Sacral 1. (This is not the same as the sacroiliac joints.) You can find some really good spinal anatomy diagrams online that will help you to visualize this.
The report indicates there is no neural compression associated with the L5-S1 disc...but an annular tear can cause a chemical reaction that is irritating to the nerve and can result in a great deal of pain...or it can be asymptomatic.