Excellent question forumnut.
I will also ask, why is the spine surgeon saying fusion?
It is excellent to seek more than one opinion, 2, 3, even 4 are good.
Also good to seek out the opinion of both orthopedic surgeons that specialize in spines only as well as neurosurgeons that specialize in spines only.
Personally, I found that neurosurgeons are far more apt to proceed with a spinal fusion right away, instead of trying more conservative types of spinal surgery.
Once a spinal fusion is done, it can not be undone. Were as if one does less radical spinal surgery and it is not successful, one can than opt for a fusion.
I have a friend who had a fusion. Her recovery was long and slow, but a year later she has almost full flexibility in her low lumbar spine.
She believes that her recovery was slow and long because of her age. She was 69 at the time, but, as she puts it "i would do it again in a heartbeat. It gave me back my life."
Good luck
Fran