Five and a half decades of riding fixed-gear bikes---I figured that, since I had only sporadic knee discomfort from time to time, I could go on grinding up climbs indefinitely. But "grinding" turned out not to have been merely a metaphor.
I'm just starting to get back to where neither of my knees is bothering me, at least if I'm careful to spin low gears at all times. I wish Chaadster all the best, but I think I'll stick with higher-cadence riding henceforth. Don't care to press my luck.