How far would I go? I would go with a consultation with an orthopedic specialist, to see if there are any surgical alternatives. This is out of the expertise of your regular vet. See what happens after the rest and medication, and if there is no improvement have the vet refer you to a specialist. You need to take all records including x-rays, and that gets you about an hour long consult with someone who does these types of surgeries, etc. It runs about $150 but it's well worth the money. Right now you are jumping ahead and making decisions that rely on either getting a cart, or putting him down. There may be several other alternatives - so check them all out with the specialist. This way you would be making an informed decision, and not one made in the heat of the moment.