The elbow is more than a simple hinge. It is designed to allow us to position our forearm so we can use our hands in many different ways. It is easy to understand how difficult many simple functions would be if your elbow did not work correctly. The elbow is a joint in which the unique positioning and interaction of the bones allows for a small amount of rotation as well as hinge action.
The elbow joint is formed when three bones come together, the upper arm bone (humerus) and the two bone of the forearm (radius and ulna). The ulna is on the inside (medial) of the elbow while the radius is on the outside (lateral). Humerus forms the upper part of the joint and widens near the end to form the medial and lateral epicondyles, which are the two bony processes on either side of the elbow.
Articular cartilage covers the ends of bones of any joint. It is a white, shiny material that is about a ¼-½ inch thick in most large joints. It allows surfaces to glide over one another without damaging either surface.
Articular cartilage functions to absorb shock and provide a slippery smooth surface to facilitate motion. In the elbow, articular cartilage covers the end of the humerus, the ulna and radial head.
There are a large number of muscles that cross the elbow joint to allow flexing and extending the elbow, rotating the hand and forearm, and straightening and bending the fingers. Most of the muscles that straighten the fingers and wrist and rotate the hand outward (supination) all come together in one tendon that attaches to the lateral epicondyle. Most of the muscles that bend the fingers and wrist and rotate the hand inward (pronation) all come together in one tendon that attaches to the medial epicondyle. These two areas are common locations of tendonitis.
There are several important tendons around the elbow. The biceps tendon attaches the large biceps muscle on the front of the arm to the forearm. It allows the elbow to bend with force. You can feel this tendon crossing the front crease of the elbow when you tighten the biceps muscle. The triceps tendon connects the large triceps muscle on the back of the arm with the forearm.
Ligaments are soft tissue structures that connect bones to bones. The ligaments around a joint usually combine together to form a joint capsule. The joint capsule is a watertight sac that surrounds a joint and contains lubricating fluid called synovial fluid. In the elbow, two of the most important ligaments are the medial and lateral collateral ligaments. These ligaments are the main source of elbow stability. Together these two ligaments connect the humerus to the ulna and keep the elbow in place as it moves through flexion and extension. These ligaments can be torn when there is an injury or dislocation to the elbow. If they do not heal correctly the elbow may become too loose, or unstable. Another important ligament is the annular ligament that forms a ring around the radial head and holds it tightly against the ulna.
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