The good news is, the spinal fusion looks great and they're very happy with things.
The less-good-but-far-from-awful news is, the minor back pain I'm having is without explanation or resolution. It's nothing that shows up in the CT scans, and given the effect of the medications elsewhere in my body it's extremely unlikely to be cancer.
It may be relieved (in whole or in part) by physical therapy--once it's safe to return to PT. It may just be pain I have to live with, and it's far from unmanageable. If it doesn't lessen over time, once PT and massage are back on the menu, I'll pursue further explanations, but for now it doesn't seem like there's much to do.