The Components of an Elbow Joint

Comprised of three separate joints, the elbows combined movements pivot, glide, flex and extend the arm. Providing flexibility and stability to the hand and forearm, this hinge joint controls the arm and the hand so that it moves with deft precision. Arm wrestling would be difficult if it were not for the stabilizing strength and mobility of the elbow joint. Try eating, drinking or working without moving your elbows.

Humeroulnar Joint

• The proximal end of the ulna is the bone visible in this photo.

  The humerus is the largest and strongest bone of the upper arm. The end of the humerus that is farthest from the body, the distal end, has a trochlea or an hourglass shape. This hourglass allows the joint to lift heavy objects without injuring the muscles. This lever system of the upper arm and forearm balances the forces needed to lift and position heavy objects. Articulating at the distal end of the humerus is the ulnar bone. The ulna fits into the hourglass shape between the two heads of the trochlear notch, creating the elbow. These heads known as the coronoid fossa or crown/front of the humerus and olecranon fossa are located at the proximal aspect of the humerus. The portion of the humerus closer to the body is the proximal end.

Humeroradial Joint

• The humerus articulates the radius to create a ball and socket system in the humeroradial joint. This mechanism permits the elbow to flex and extends while the forearm pivots. The hand and forearm supinate or turn upward and outward and pronate, rolling inward and downward. These rolling supination and pronation actions move the arms and hands in a variety of directions that enable you to eat, drink, dress and influence your environment. The proximal head of the radius, the head that is closest to the torso, rides along the distal aspect of the humerus, attached by ligaments. The radius rests on the radial notch of the ulna, attaching underneath the humerus. With arms resting at the side of the body, the palms facing forward, establishing the outer, thumb side of the elbow as the humeroradial joint.

Proximal Radioulnar Joint

• The radius and the ulnar articulate with the proximal humerus and ride on the carpal bones, distally.

  Imagine drawing a triangle at the bottom of the humerus. Within that triangle, these three joints articulate. Allowing the forearm and hand to pivot, flex and extend, the humeroulnar, the humeroradial and the proximal radioulnar joints complete this complex elbow joint. The radius and the ulna rest on the inside of the two bones, attached with ligaments, tendons and muscle. These attachments allow the forearm and elbow to roll and weave in the socket. When you eat, read the paper, or put on your clothes, you operate this rolling and twisting motion. The proximal radial head rests on the distal aspect of the humerus, allowing the elbow to flex and extend while the forearm pivots. The radial head rests on the radial notch of the ulna to create the radioulnar joint.

Muscles of the Elbow Joint

• The human body supported by the bones of the skeleton is unable to move without muscles. The hands and forearms flex, extend, supinate and pronate because of the coordinated muscle movements of the triceps and the anconeus. These muscles provide extension to the elbow joint and forearm. The brachialis, biceps brachii and brachioradialis work together to flex the elbow joint that attaches the upper arm and forearm. The muscle fibers of the supinator and the biceps assist the forearm and hand to revolve upward and outward. The pronator quadratus and the pronator teres pronate the forearm so that it rotates in the opposite direction, downward and inward.