This condition is a fracture of the head of the humerus - the "ball" of the shoulder's ball-and-socket.
This type of fracture can be caused by direct trauma to the shoulder. It commonly affects elderly people whose bones have been weakened by osteoporosis.
Symptoms include severe pain, swelling, and inability to move the arm.
Treatment options depend on the severity of the fracture. If the bones have not shifted, the fracture may be treated with a sling. If the bones have become displaced, surgery is needed to realign and anchor the bones or to replace the joint.