The elbow is a hinge-joint between the bones of the upper and lower arm. It joins the humerus of the upper arm and the radius and ulna of the forearm together. Everyone has 2 elbows. It allows the lower arm to be extended or retracted (moved in). The elbow also allows the arm to turn. It moves by using three ligaments: the "anterior, posterior, ulnar collateral" and "radial collateral" ligaments.