In reply to Martin Hore:
I've had surgery for spinal stenosis caused by spondylolisthesis. It started with similar syptoms of numbness creeping up the legs and quite quickly deteriorated to the point where I had to stop for a rest walking down the corridor at work - a bit of a come down from walking 30 miles or more a week (although I'd moved on to more paddling than walking by the time this hit). Oddly scrambling remained easier than "easy" walking or standing.
The GP referred me to the physio who promptly referred me to the Walton Centre, where I was lucky to wind up in the hands of a surgeon whose special interest this was. Exercise was not remotely likely to fix it, it was deteriorating quite fast and I was warned of the risk of nerve damage becoming permanent if left too long. I seem to have wiped the exact terminology from my memory but I was given options involving fusion and metalwork, or a non-metal option involving taking the misplaced vertebra apart, clearing space for the nerves, and jigsawing it back together again. The latter is the option I chose.
Apparently many people take only a day or two before walking normally - it took a little longer for me and the few days after the operation were very painful indeed. But the day I went home I could walk a mile without even thinking about stopping for the first time in over a year. I'd had no idea how handicapped I'd been until I suddenly wasn't.
Don't know how the recovery would have gone if I hadn't overreached and pulled something while stretching, which led to more painful days. Nearly three years on I'm not in the same state I was before it started going wrong, but infinitely better than I was just before the operation. Things I particularly noticed: I seemed to have lost a lot of shock absorption so running really jarred; heavy rucksacks were not sensible; the fine control I needed for balancing a racing kayak was definitely diminished and I lost some flexibility. The irony is that before the operation my back didn't hurt at all, but now it does - on the other hand, I was not functional at all but now I'm almost back to normal and hopefully still improving.
As you remarked, they did find it unusual to have a young(ish) active patient. The physio was very sympathetic to my wish to get right back into activity, though not to the extent of putting it in writing that I needed to paddle every day...Joking apart, though, the paddling does help keep my back loose and I notice if I don't do it a while. Flexibillity is coming back if I remember to stretch, running begins to seem possible again (if my knees let me), cross-country skiing no problem, climbing no problem apart from the wretched knees (but I'm not a hard climber anyway), and I'm getting back to carrying heavier weights. The one thing that still makes me ache is standing for any length of time.
Anyway, I guess the short message from this long ramble is that for me surgery was definitely the right choice, done sooner rather than later. The non-metalwork non-fusion option has worked well for me too. One of the hardest lessons to learn was that it would take so long to get back towards normal - but that it is getting there however slowly. The other hard lesson is to listen to my back and ease off or rest it if I've been pushing too hard.
Hope this helps, and good luck with your decision.