Full Muscles of the Shoulder Description
[Continued from above] . . . of the head of the humerus with the scapula. It is a ball-and-socket joint and the most freely moveable joint in the body. The shoulder joint is protected above by an arch formed by the coracoid process and acromion process of the scapula and by the clavicle. Although three ligaments protect and surround the shoulder joint, most of its stability comes from powerful muscles and tendons that pass over it. It is an extremely mobile joint, in which stability has been sacrificed for mobility. Dominated by the deltoids over the ball of the shoulder, the muscles of the shoulder effectively include even the pectoral muscles of the chest, the trapezius continuing up the neck and down the back, the muscles of the upper arm, the rhomboids of the scapula, and a host of smaller muscle groups attached to the ribs and other parts of the skeleton.
Although the joint is held together by these extensive ligament and muscle attachments, certain types of forces can weaken the shoulder easily. The shoulder joint is vulnerable to dislocations from sudden jerks of the arm, especially in children before strong muscles have developed. Because of the weakness of this joint in children, parents should be careful not to force a child to follow them by yanking on their arm. Dislocation of the shoulder is extremely painful and may require surgical repair or even cause permanent damage.