Roxanne,
It seems like from reading this forum over the years that extension of the fusion into the bottom lumbar levels is pretty common. It is done with the goal of reducing pain or stabilizing a progressive curve. No guarantees, but many people seem happy with the final outcome as far as pain reduction.
I was fused t4-sacrum last March. I was on pain meds (mostly Norco) for 5 months. I still have some back pain, but I usually do not get that achy lower back or sciatica-like nerve pain that I did pre-op. My pain now is upper back tightness and pain in the sacrum/hip area when I walk too long or too fast. For me, surgery has made walking more difficult, but standing is easier. However, I didn't have much pain pre-op. it seems like anecdotally people with significant preop pain do tend to get relief from revision surgery.
Best wishes,
Evelyn
age 48
80* thoracolumbar; 40* thoracic
Reduced to ~16* thoracolumbar; ~0* thoracic
Surgery 3/14/12 with Dr. Lenke in St. Louis, T4 to S1 with pelvic fixation
Broken rods 12/1/19; scheduled for revision fusion L1-L3-4 with Dr. Lenke 2/4/2020
Not "confused" anymore, but don't know how to change my username.