Radial Head of the Elbow: Function, Anatomy, and Clinical Significance

What is the function of the radial head of the elbow?

The radial head is a crucial component of the elbow joint, primarily facilitating pronation and supination of the forearm while also contributing significantly to elbow flexion and extension stability.

Anatomy of the Radial Head

The radial head is the proximal, disc-shaped end of the radius bone, one of the two long bones of the forearm. Its unique anatomical structure allows for both rotation and articulation with the humerus and ulna:

• Disc-shaped Articular Surface: The superior surface of the radial head is concave, forming an articulation with the convex capitulum of the humerus. This allows for flexion and extension of the elbow.
• Cylindrical Articular Surface: The medial aspect of the radial head is smooth and cylindrical, articulating with the radial notch of the ulna. This articulation, along with the strong annular ligament that encircles the radial head, forms the proximal radioulnar joint, which is pivotal for forearm rotation.

Primary Function: Forearm Rotation (Pronation and Supination)

The most distinctive and critical function of the radial head lies in its role in forearm rotation. This movement occurs at the proximal radioulnar joint, where the radial head pivots within the annular ligament and against the radial notch of the ulna.

• Supination: This is the movement that turns the palm upward or forward (anatomical position). During supination, the radial head spins laterally, causing the radius to cross over the ulna in its distal part. Key muscles involved include the biceps brachii and supinator.
• Pronation: This is the movement that turns the palm downward or backward. During pronation, the radial head spins medially, causing the radius to cross over the ulna, bringing the thumb side of the hand towards the body. Key muscles involved include the pronator teres and pronator quadratus.

This rotational capability is fundamental for countless daily activities, from turning a doorknob to using tools, eating, or performing various exercises.

Secondary Function: Contribution to Elbow Flexion and Extension

While the primary articulation for elbow flexion and extension is between the trochlea of the humerus and the trochlear notch of the ulna (forming the humeroulnar joint), the radial head also plays an important, albeit secondary, role.

• Articulation with the Capitulum: The radial head articulates with the capitulum of the humerus, forming the humeroradial joint. This joint permits gliding and rolling movements during elbow flexion (bending the elbow) and extension (straightening the elbow).
• Load Bearing and Stability: The humeroradial joint contributes to the overall stability of the elbow, especially during activities that involve compression or axial loading of the forearm, such as pushing or weight-bearing exercises. It helps distribute forces across the joint.

Ligamentous and Muscular Support

The function of the radial head is heavily reliant on the integrity of surrounding ligaments and the action of specific muscles:

• Annular Ligament: This strong, fibrous band encircles the radial head, holding it firmly against the ulna's radial notch. It is essential for maintaining the stability of the proximal radioulnar joint and enabling smooth rotation.
• Lateral Collateral Ligament Complex: This complex, particularly the radial collateral ligament, originates from the humerus and blends with the annular ligament, providing lateral stability to the elbow and supporting the radial head.
• Muscles of Forearm Rotation: As mentioned, the biceps brachii and supinator are powerful supinators, while the pronator teres and pronator quadratus are the primary pronators. These muscles act on the radius, causing the radial head to rotate.

Clinical Significance and Injury

Given its critical roles, the radial head is susceptible to specific injuries that can severely impact elbow function:

• Radial Head Fractures: These are common elbow fractures, often resulting from a fall onto an outstretched hand. They can impair both rotational and flexion/extension movements.
• Nursemaid's Elbow (Pulled Elbow): This common pediatric injury occurs when a child's arm is suddenly pulled, causing the radial head to sublux (partially dislocate) from under the annular ligament. It typically results in pain and an unwillingness to use the arm.
• Osteoarthritis: While less common than in weight-bearing joints, the humeroradial joint can develop osteoarthritis, leading to pain and reduced range of motion, particularly in rotation.

Practical Implications for Movement and Training

Understanding the radial head's function is vital for optimizing movement and preventing injury in fitness and daily life:

• Exercise Selection: Exercises that involve forearm rotation (e.g., hammer curls, bicep curls with supination, pronated/supinated grip rows) directly engage the muscles acting on the radial head and benefit from its mobility.
• Rehabilitation: For individuals recovering from elbow injuries, targeted exercises to restore radial head mobility and strength in pronation and supination are crucial for functional recovery.
• Overuse Syndromes: Repetitive forearm rotation can contribute to conditions like tennis elbow (lateral epicondylitis), which, while primarily affecting extensor muscles, can be exacerbated by stresses transmitted through the radial head.

In conclusion, the radial head, though small, is an indispensable component of the elbow, orchestrating the vital movements of forearm rotation and contributing foundational stability to the entire joint. Its proper function is paramount for a wide array of human activities.