Well, one of the problems (as others have mentioned) is that your pain is chronic. A lot of doctors feel that they are actually doing you a disservice to prescribe something so addictive for chronic pain, seeing as once you get used to Vicodin (or any other opiate) it is literally hell to get off of. Then you will not only have terrible knee pain, you’ll also have terrible withdrawal. I personally wish I’d never, ever seen or heard of any kind of opiate.
But if no other painkillers work, I think you should just talk to another doctor, possibly one at a pain clinic. Just seeing another doctor doesn’t necessarily mean you need to completely give up your regular doc of 20+ years… it just means maybe you can find one more amenable to prescribing opiates.