15% of the 600,000 knee replacements each year suffer severe pain after the operation. The pain usually starts soon after the surgery and can last indefinitely. My experience is that it can usually be treated pretty well with a healing laser. However, the best approach might be to try prolotherapy injections prior to the surgery, and you might be able to avoid the need for surgery completely.
See getprolo.com (click here) and healthcelebration.com (click here)