Get to know the science behind what causes the stiff, creaky joints of the most common forms of arthritis and what you can do to prevent it. — The bad backs, elbow pain, and creaky knees so common in older people often aren’t just “old age.” In fact, the source of this stiffness plagues many young people as well. The culprit is arthritis: a condition that affects over 90 million people in the U.S. alone. What makes arthritis so pervasive, and why haven’t we found a cure for it? Kaitlyn Sadtler and Heather J. Faust investigate. Lesson by Kaitlyn Sadtler and Heather J. Faust, directed by CUB Animation.