A fusion is required in the face of nerve pain only (no real lower back pain) only if the vertebra is incapable of maintaining alignment and this malalignment is causing nerve root compression.
For example, if there is an angular collapse of the right side of L5 on S1 (the intact disc normally keeps the two vertebral bodies parallel to each other) because the disc is asymmetrically worn out on the right side, this could compress the L5 nerve in the foramen. If a simple decompression is used (no fusion) and more bone is removed to make room for the nerve, this procedure will fail. The removed bone will allow further collapse of L5 on S1 and the same leg pain will recur within a couple of months.
Now if you only complain of leg pain (no lower back pain) and the vertebra is stable, then a simple decompression surgery only would be recommended.
As you can see, there is no perfect answer to your question. Go back to both surgeons and ask why they had chosen that particular surgery now based upon your new knowledge. Why does the spine surgeon recommend fusion? Make him give good reasons for his decision. Also challenge the neurosurgeon to see if he can explain why his surgery will not destabilize the level. By listening to both, you will gain more understanding and be able to choose correctly.
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.