Each shoulder has two joints that connect three bones, the collarbone (clavicle), the shoulder blade (scapula), and the humerus, which is the long bone in the upper arm. These two joints allow you to rotate your arms in multiple directions. The top of the humerus lies on a shallow shelf of shoulder bone like a golf ball on a tee. Some shoulders dislocate easily because the humerus falls off the shelf. This ball-on-a-tee joint allows you to swing a golf club or a tennis racket, do the butterfly stroke or the backstroke, or wave wildly to your best friend bopping down the street.
Find out more about this book:YOU: The Owner's Manual for Teens: A Guide to a Healthy Body and Happy Life