@rackmaster20, oh, good!
There is a procedure called hardware augmentation, https://pmc.ncbi.nlm.nih.gov/articles/PMC10622820/, though the gap may not be accessible.
And the gap may not be the cause of your pain and swelling
You might ask about romosozumab and teriparatide the two bone anabolic medications. I hope you find out why this happened. And if the implant is stable.
You might (not) enjoy reading this https://www.spine-health.com/treatment/spinal-fusion/failed-spinal-fusion-surgery.
I hope your doctor has all the answers and it's minor revision rather than replacement.