The reason you did not fuse anteriorly has to do with the technique used. The PEEK cages (I assume were used) are made of plastic and have no biological ability to heal themselves. Only whatever graft is placed into them can heal. This reduces the surface area for healing and makes these cages less effective for fusion.
If you had your own bone used the second time around (called autograft), this increases your chances of healing greatly. The bed has to be meticulously prepared (the old surfaces of the vertebral bodies) by hand milling these surfaces until they are parallel (see the video on ACDF to understand this).
There is a chance that a posterior foraminotomy will work but the chances of success are less than a redo of the anterior surgery. I would say 70% vs 90-95%.
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.