Isthmic spondylolisthesis lower back pain generally emanates from the disc and the pars fractures. Leg pain originates from the foraminal stenosis. Radio frequency ablation generally does not yield relief. I cannot count how many patients have come into my office after having this procedure without relief.
In my opinion, based upon your history and symptoms, you will need surgery for stabilization of this level. The most typical surgery is a TLIF. See the website for a description.