Orthopaedics spine surgeons generally have a higher success rate with lumbar fusions. 50% of the work I do is revision surgery (when the initial surgery did not work) and generally it is for pseudoarthrosis (failure of fusion).
80% of the failures originate from neurosurgeons so simply based upon that, you are probably better off with a spine surgeon to take care of this fusion failure. I understand you had a spine surgeon for your initial surgery and this failure might put you off.
If you do have a failure of fusion, a rhizotomy will not be helpful. Remember that the facets should have been ablated (removed or burred down to bone underneath) to allow for fusion. If they were not touched during surgery (and I have seen that not uncommonly), they need to be fused.
Dr. Corenman
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.