Based upon your complaints of lower back pain, this sounds like IDR. Foraminal stenosis causes buttocks and leg pain generally with standing and walking that is relieved with sitting and forward flexion. IDR is treated with a fusion.
If you need a fusion, either a spine surgeon (an orthopedist with a fellowship in spine surgery) or a neurosurgeon should do. Just make sure you do your research and read up on this individual. All surgeons are not the same.
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.