The elbow is a strong, practical joint. It is what is classified as a hinge joint. The elbow allows movement forward and backward as well as rotation. This joint is created with the coming together of the humerus, the strong upper arm bone, and the radius and ulna bones that make up the forearm.
The basic construction of the elbow joint
The base of the humerus spreads out in two rounded projections called the epicondyles with a ridge called the trochlea between the two extensions of bone. The radius, located on the thumb side, and ulna is located on the little finger side, are the two bones making up the forearm. They come together creating the proximal radioulnar joint. The ulna, with its crescent shape, is able to slide into the olecranon fossa of the humerus when the elbow is extended. When the elbow is flexed, it fits into another depression on the anterior or front surface of the humerus. It is the radioulnar joint that permits the rotation of the forearm so the palm can face downward (pronation) and upward (supination).
Cartilage for smooth movement
As in all joints, the ends of the bones are covered in a material called articular cartilage. In joints that involve weight bearing, the cartilage can be up to one-quarter of an inch thick, but elbow does not require such thickness. It is white in color, shiny and has a rubbery consistency. The slippery finish allows the joint surfaces to slide smoothly against each other without causing damage. The cartilage also absorbs shock.
Ligaments bind all together and allow movement
The main ligaments are the ulnar collateral ligament and the radial collateral ligament. They are fan shaped and form the fibrous joint capsule. The joint capsule is a watertight sac that surrounds the joint and it contains lubricating fluid known as synovial fluid.
The ulnar collateral ligament stabilizes the medial or inner side of the joint. This ligament prevents excessive abduction of the elbow joint (movement away from the body). The radial collateral ligament stabilizes the lateral or outside of the joint and prevents excessive adduction movement (movement toward the body). The annular ligament encircles the head of the radius and thus binds it to the ulna.
Nerves of the elbow
There are three major nerves within the upper extremity. They are the radial, ulnar and median nerves and the pass through the elbow on their way to the hand. The ulnar nerve which passes close to the surface, is the nerve that reacts when the elbow is bumped. It produces a tingling or numbness when it is compressed.
Tendons connected to the elbow
The biceps tendon attaches the radius to the large bicep muscle on the front of the arm. It allows the elbow to bend with force and is visible when you tighten the biceps muscle. The triceps tendon connects the ulna to the triceps muscle on the back of the arm. This combination allows you to straighten the elbow with force as when doing a push-up. Most of the muscles that allow you to bend and straighten the fingers and wrist, all come together in one tendon for each function and attach.
Yes, it is a simple hinge, but the design and intricate connection of the bones, the tendons and muscles, not only provide maximum stability, but also mobility in many ways.