 Try to pay off your debts within the month they're charged and you'll avoid paying interest. For more, check out Bankrate.com. On the Health Watch this afternoon, here's Elizabeth Tracy. The shoulder joint is known as a ball and socket, where the ball part is part of the arm bone called the humerus, while the socket is part of a bone known as the scapula. Edward McFarlane, head of shoulder surgery at Johns Hopkins, says the tendons surrounding the joint are of paramount importance, forming a structure called the rotator cuff.