I injured my knee climbing the city walls of Dubrovnik and found after a few days that I could hardly walk at all. Standing was no problem, but walking? Not so good. When I got back to the U.S., I went to a chiropracter, thinking it was merely out of place. He said it was a little, but that he suspected calcium deposits had been "knocked loose" in the climbing and that the knee wouldn't be much better until they were out of my knee area (not a surgical thing, just normal blood cleansing the area), and that he thought I should go to my doctor for his opinion. As it turned out the doctor was essentially useless and wanted to remove fluid (which I maintained wasn't there--and he discovered with his needle wasn't there) and inject steroids (which changed absolutely nothing.)
The chiropracter said the knee was aligned properly and loaned me a tens unit so that I would be able to walk while we were in Yellowstone. It was invaluable. It still hurt some, but I could walk, slowly, but I managed most sights. I simply couldn't have done it without the tens unit. For me, the relief lasted quite a while, and by using it after a walk, I was able to do the next one. After I returned the loaner unit, I bought one to keep on hand, even though the calcium deposits cleared the knee shortly after we got back from Yellowstone. I like knowing I have it if I should need it again.