The elbow is a joint connecting the lower arm, or forearm, with the upper arm. The elbow joint interconnects the radius and ulna bones of the lower arm with the humerus bone of the upper arm. This connection is formed through a series of muscles, ligaments and tendons. The upper arm muscles pass over the elbow joint and connect to bones of the forearm. Similarly, muscles of the forearm cross the elbow joint and attached to the humerus bone of the upper arm. This crossing of muscles provides for elbow stability, and arm movement at the elbow.
There are eight sets of muscles passing over the elbow. These are the biceps brachii, triceps brachii, brachioradialis, brachialis, pronator teres, pronator quadratus, anconeus, and supinator.
The biceps brachii connects from the scapula in the shoulder to the upper part of glenoid fossa in the forearm. It is responsible for flexing or bending the elbow. The brachioradialis connects from the lower part of the humerus bone in the upper arm to the lower part of the radius bone in the forearm. The brachialis connects from the lower part of the humerus bone in the upper arm to the upper part of the ulna bone in the forearm. The brachioradialis and brachialis are also responsible for bending the elbow.
The triceps brachii connects the scapula and upper humerus with the upper part of the ulna in the forearm. It is responsible for extension or straightening of the arm. The anconeus connects the humerus with the upper ulna bone and is also responsible for forearm extension.
The pronator teres connects from the lower humerus to the lower ulna. It is responsible for pronation, or inward rotation of the forearm at the elbow. This means a counterclockwise twist for the right forearm, and a clockwise twist for the left forearm. The pronator quadratus connects between the ulna and the radius, and also helps with pronation of the forearm.
The supinator connects the lower humerus with the upper radius. It is responsible for supination of the lower arm. This is the opposite rotation to the pronator muscles. Supination means outward rotation of the forearm, that is clockwise twist for the right forearm, and a counterclockwise twist for the left forearm.