Anatomy of the Elbow
The elbow is a joint that hinges and pivots, allowing the arm to bend, extend and rotate. Although usually thought of as having a single joint, the elbow actually has three, created by the meeting of three bones, the humerus, ulna and radius. Ligaments hold the bones together, and the ends of the bones are covered with cartilage, which allows them to slide easily against one another and to absorb shock.
Damage to the elbow may be the result of traumatic injury, overuse from repetitive-motion tasks or sports, or from aging in general. Injury to any part of the elbow can be debilitating and painful, and should be evaluated by a medical professional.
Bones and Cartilage in the Elbow
Where they meet, the elbow's three bones have articular cartilage, which is material that covers the joints found at the ends of bones. White, shiny, rubbery and slippery, it enables the surfaces of the joints to slide against one another without causing damage. Articular cartilage is found anywhere that two bony surfaces that move against one another, or articulate. The three bones found in the elbow are:
- Humerus, the upper arm bone, extending from elbow to shoulder
- Ulna, the larger of the forearm's two bones, on the opposite side of the thumb
- Radius, the smaller of the forearm's two bones, on the same side as the thumb
The joint in the elbow where the humerus meets the ulna allows the arm to be bent and extended, and the palm turned up or down. The joint where the radius meets the humerus allows the arm to be rotated, but is not involved in bending or straightening.
Ligaments and Tendons in the Elbow
The elbow contains a number of ligaments, which are soft tissue that hold bones together. Two of the elbow's ligaments connect the humerus to the ulna, providing the main source of stability for the elbow. They are the medial collateral ligament, located on the inside edge of the elbow, and the lateral collateral ligament, located on the outside edge of the elbow. These ligaments can be torn when there is an injury or dislocation to the elbow and, if they do not heal correctly, may cause the elbow to become "loose." A third ligament, the annular, encircles the head of the radius, holding it firmly in place against the ulna.
The elbow also contains tendons essential for its correct operation. They include the biceps tendon, which attaches the biceps muscle on the front of the arm to the radius, allowing the elbow to be forcefully bent, and the triceps tendon, which attaches the triceps muscle on the back of the arm to the ulna, allowing the elbow to forcefully straighten.
Muscles in the Elbow
Like the biceps and triceps tendons, the biceps and triceps muscles that surround the elbow enable the arm to be bent or straightened at the elbow. There are also muscles in the elbow involved in wrist and finger movement. They are the flexors, which attach to the inside of the elbow, and enable the wrists and fingers to bend, and the extensors, which attach to the outside of the elbow, and enable the wrists and fingers to straighten.
Nerves in the Elbow
The three main nerves begin in the shoulder and run down through the elbow. The radial, ulnar and medial nerves carry signals to the brain that are responsible for movement and sensation. These nerves may become a problem from the elbow's continual bending and straightening, which can put pressure on or irritate the nerves. Pain, numbness and weakness in the hand can all result from nerve damage in the elbow.