The problem with the internet is that often the only
reports you see there are of surgeries that didn't turn out well. If you find yourself an experienced veterinary orthopedic surgeon, the chances of your dog having a successful outcome far outnumber the chance of a bad outcome.
The most important part of any orthopedic surgery is follow-through--the more closely you follow the surgeon's post-operative instructions (including following recommendations for exercise or rest and prohibited behaviors while healing), the better your dog's results usually are.
So if you're willing to commit to getting your dog through recovery, and go with a good surgeon, your dog will likely do well!
There can be complications with any
surgery, of course, but you can't guarantee there would be none with something as radical as an amputation, either. In addition, changing his balance by amputating a leg is going to put extra torque and strain on the spine. That will likely accelerate the progress of the spondylosis. Also, many dogs that blow out one ACL will blow out the other. Amputation of the damaged leg now will not guarantee that the other ACL won't tear in the future--and recovery is much harder if you do ACL surgery in that situation since the dog can't rest the leg by taking its weight on the other.
If it were me, I'd locate a good surgeon and start asking lots of questions...including the number of surgeries the vet has done and the percentage of failures. Reputable vets should have no problem with you asking about their credentials.
Best of luck with your dog, cross222.