The labrum is like a roller rink in the shoulder. The head of humerus (arm bone) rolls around on the labrum to allow for arm movement. Cartilage makes up the labrum but can be torn or damaged with an injury or repetitive motions. When the labrum tears, it is like the roller rink loses a few floor boards usually on the outer edge. Just like skaters on a roller rink, there is a significant chance the humerus will roll right off the labrum during shoulder movement. This can cause pain or a clunking feeling in the shoulder.