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. [Directed by CUB Animation, narrated by Bethany Cutmore-Scott, music by James Wood].