You are fused from T4 through S1 (I assume solidly) so the T8 compression fracture should not be an issue. The T4 fracture is not uncommon as T4 Is a stress riser right at the end of your fusion with a long lever arm and osteoporosis makes the vertebra more susceptible to fracture. I assume that the old chronic fracture is painful as many old compression fractures can become non-painful over time.
Radiofrequency ablation (RFA) can be helpful if the facets at T3-4 are painful. There is an easy way to test that hypothesis and that is facet blocks of the nerves that supply these particular facets. See the attached hyperlinks. If you gain good temporary relief, you could be a candidate for RFA. If this facet block does not work, consideration can be given to vertebroplasty, a technique where cement is placed into the fractured vertebra. Finally, an add on fusion could be considered if nothing else works and this level is proved to be the pain generator..
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.