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.