If you have a solid anterior fusion, the force of weight bearing goes through the old (now fused) disc space and very little goes through the posterior elements (which includes the pars fracture). Repairing the pars fracture (especially a unilateral one) would be similar to using a q tip to clean your car after you go through a car wash. You can do it and you could find more dirt but the difference would be negligible.
What you need really boil down to is to find the current pain generator. The best bet is the nerve root as you had significant pain after your surgery in this leg. When the nerve becomes less irritable, it “centralizes” (the pain retreats to the SI and buttocks region only). Since you never had a posterior surgery, the nerve still could be compressed. In addition, as we discussed before, you could still have a non-union of the L5-S1 segment and you need a CT scan to determine this possibility.
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.