I don't know anything about knees, but agree that riding injured is hardly worth it. I tore my rotator cuff in Feb last season, and thought about putting surgery off until after the season. I went riding once after it was torn, and even with being tentative (which took much of the fun out of it) it was impossible not to aggravate. I could barely drive home (shifting gears) from the slope, and couldn't get my arm out to parallel from the ground for a week afterwards. I called it a day and had the surgery before I really hosed myself. I also seem to remember reading/hearing at the time that repairing tears quickly leads to fuller recovery.