By Pure Matters Whether throwing a ball, paddling a canoe,
lifting boxes or pushing a lawn mower, we rely heavily upon our
shoulders to perform a number of activities. Normally, the
shoulder has a wide range of motion, making it the most mobile
joint in the body. Because of this flexibility, however, it is
not very stable and is easily injured. The shoulder is made up
of two main bones: the end of upper arm bone (humerus) and the
shoulder blade (scapula). The end of the humerus is round, and
it fits into a socket in the scapula. The scapula extends around
the shoulder joint to form the roof of the shoulder, and this
joins with the collar bone (clavicle). Surrounding the shoulder
is a bag of muscles and ligaments. Ligaments connect the bones
of the shoulders, and tendons connect the bones to surrounding
muscle. Four muscles begin at the scapula and go around the
shoulder, where their tendons fuse to form the rotator cuff.
When the shoulder moves, the end of the humerus moves in the
socket. Very little of the s