The elbow is a complex joint system that connects the upper arm to the forearm. This junction facilitates a wide range of motion, enabling the hand to be positioned in the space around the body. The elbow’s structure is fundamental to everyday actions, from lifting objects to self-care.
Identifying the Bones That Form the Elbow
The elbow joint is formed by the articulation of three distinct bones: the humerus, ulna, and radius. The humerus is the single bone of the upper arm, and its lower end forms the upper portion of the joint. The ulna and the radius are the two bones of the forearm that meet the humerus. The ulna is the larger forearm bone, located on the side of the little finger, forming the prominent bony point of the elbow. The radius is the smaller forearm bone, situated on the thumb side, and is involved in rotational movement.
Anatomy and Joint Structure
The three bones articulate to form three separate, interconnected joints contained within a single capsule. The Humeroulnar joint is the primary articulation, functioning as a hinge to allow for bending and straightening of the arm. Here, the trochlea of the humerus fits into the trochlear notch of the ulna. The Humeroradial joint, where the head of the radius meets the capitulum of the humerus, contributes to both hinging motion and forearm rotation.
The third joint, the Proximal Radioulnar joint, is a pivot joint formed by the head of the radius rotating within a notch on the ulna. Articular cartilage covers the ends of all three bones, reducing friction and absorbing shock. Stability is provided by a network of connective tissues called ligaments that form a surrounding joint capsule. The Medial and Lateral Collateral Ligaments brace the joint on either side to prevent excessive side-to-side motion.
Range of Motion and Function
The elbow allows for two main types of movement: hinging and rotation. Hinging motion, facilitated primarily by the humeroulnar joint, includes Flexion (bending the arm toward the shoulder) and Extension (straightening the arm). The ulna’s shape allows for a range of motion from nearly full extension to around 135 to 150 degrees of flexion. This movement is powered by the biceps and triceps muscles, respectively.
Rotational movements are enabled by the proximal radioulnar joint, allowing the hand to turn over. Pronation turns the palm to face downward or backward. Supination is the opposite action, rotating the forearm to make the palm face upward or forward. These rotational capabilities allow the hand to be oriented correctly for grasping and manipulating tools.
Common Elbow Injuries and Conditions
One of the most common issues affecting the elbow involves inflammation of the tendons, a condition broadly known as epicondylitis. Tennis Elbow, or lateral epicondylitis, causes pain on the outside of the elbow where the extensor tendons attach to the lateral epicondyle of the humerus. This condition often results from repetitive gripping or wrist extension. Conversely, Golfer’s Elbow, or medial epicondylitis, affects the flexor tendons on the inner side of the joint, typically caused by repetitive wrist flexion or forceful gripping motions.
Elbow fractures are another frequent injury, often resulting from a direct fall onto the elbow or a fall onto an outstretched hand. These traumatic events can cause breaks in the humerus, the radius, or the ulna, with the olecranon—the pointed tip of the ulna—being a common fracture site. Treatment for fractures often involves immobilization with a cast or splint, though complex breaks that affect the joint surface may require surgical realignment using plates and screws.
Bursitis is characterized by inflammation of the olecranon bursa, a small, fluid-filled sac situated directly over the bony point of the elbow. The bursa normally functions as a cushion to reduce friction between the bone and skin, but direct trauma or prolonged pressure, such as leaning on a hard surface for extended periods, can irritate it. This irritation causes the bursa to swell and fill with excess fluid, leading to pain and noticeable swelling at the back of the elbow. Initial management for bursitis and epicondylitis often involves rest, ice application, and non-steroidal anti-inflammatory drugs (NSAIDs) to reduce swelling and pain.