I have never heard of the bubbles of fluid theory. I am an orthopedic nurse in the OR at Stanford and I have never heard the docs speak of gaps or bubbles of fluid. Tears in the medial meniscus is what we mostly see....as long as we don't crash like some of those guys in the skid competitions....we shouldn't be messin with our meniscus on our bikes. Perhaps the pain some people are feeling is the stretching of the tendons and ligaments. Inflammed bursa in the knees as well as inflammed plica can also cause pain. Google plica and bursa.