Radial Head Injuries: Subluxation, Dislocation, and Key Differences

What is the difference between a radial head subluxation and a dislocation?

While both radial head subluxation and dislocation involve the displacement of the radial head from its normal articulation, a subluxation is a partial, often easily reducible displacement, whereas a dislocation is a complete separation of the joint surfaces requiring more significant force and often more complex intervention.

Understanding the Elbow Joint and the Radius

To appreciate the nuances between a radial head subluxation and a dislocation, it's essential to first understand the anatomy of the elbow. The elbow is a complex hinge joint formed by three bones: the humerus (upper arm bone), the ulna (forearm bone on the pinky side), and the radius (forearm bone on the thumb side). The radial head, the top portion of the radius, articulates with the capitellum of the humerus and also with the ulna at the proximal radioulnar joint. Crucially, the radial head is encircled and stabilized by the annular ligament, a strong band of connective tissue that holds it firmly against the ulna.

Radial Head Subluxation (Nursemaid's Elbow)

Radial head subluxation, commonly known as "Nursemaid's Elbow" or "Pulled Elbow," is a frequent injury in young children, typically under the age of five.

Definition

A radial head subluxation occurs when the radial head partially slips out from under the annular ligament. It is not a complete separation of the joint surfaces but rather a partial displacement.

Mechanism and Causes

This injury almost exclusively results from a sudden traction force applied to an extended and pronated arm. Common scenarios include:

• Pulling a child up by one hand: A parent or caregiver lifting a child forcefully by the hand or wrist.
• Swinging a child by the arms: Playful swinging that exerts a pulling force.
• Catching a child by the hand: Preventing a fall by grabbing the child's hand. The annular ligament, which is relatively lax in young children, can easily slip over the radial head when subjected to such a pulling force, becoming entrapped between the radial head and the capitellum.

Symptoms

Symptoms are often immediate and distinct:

• Sudden pain: The child will typically cry out immediately after the injury.
• Refusal to use the arm: The child will often hold the arm close to the body, slightly flexed at the elbow, and refuse to move it (pseudoparalysis).
• No visible deformity: Unlike dislocations, there is usually no swelling, bruising, or obvious deformity.
• Limited range of motion: Attempts to move the arm, especially supination (turning the palm up), will cause pain.

Diagnosis

Diagnosis is primarily clinical, based on the history of the injury and physical examination. X-rays are often taken to rule out a fracture, but they typically appear normal in a radial head subluxation.

Treatment and Reduction

Treatment is simple and highly effective:

• Manual reduction: A healthcare professional (physician, nurse, or even a trained parent under guidance) can typically reduce the subluxation with a specific maneuver. The most common techniques involve a combination of supination of the forearm and flexion of the elbow, or hyperpronation.
• Immediate relief: Often, a click or pop is felt during reduction, and the child will immediately regain use of the arm, sometimes within minutes.
• No immobilization: Once reduced, no casting or splinting is usually required.

Prognosis and Prevention

The prognosis is excellent, with full recovery common. Recurrence is possible, so parents are advised to avoid pulling on a child's arms or hands.

Radial Head Dislocation

A radial head dislocation, in contrast to a subluxation, is a much more severe and less common injury, especially in isolation.

Definition

A radial head dislocation involves the complete separation of the radial head from its normal articulation with the capitellum of the humerus and the ulna. The annular ligament is typically torn or severely stretched.

Mechanism and Causes

Dislocations of the radial head are rare as isolated injuries and usually result from:

• High-energy trauma: Falls from a significant height, direct blows to the elbow, or motor vehicle accidents.
• Complex elbow injuries: Often occur in conjunction with fractures of the ulna (Monteggia fracture-dislocation), humerus, or other significant ligamentous injuries to the elbow.
• Congenital conditions: Some individuals are born with a congenitally dislocated radial head, which is different from a traumatic injury.

Symptoms

Symptoms are typically more severe and indicative of a major injury:

• Severe pain: Intense, persistent pain in the elbow.
• Obvious deformity: The elbow may appear visibly deformed, and swelling and bruising are common.
• Complete loss of function: The arm cannot be moved normally, and any attempt at movement causes excruciating pain.
• Palpable displacement: The radial head may be felt out of place, often posteriorly or anteriorly.

Diagnosis

Diagnosis requires:

• Clinical examination: Assessment of pain, swelling, deformity, and range of motion.
• X-rays: Crucial for confirming the dislocation and identifying any associated fractures (e.g., ulnar fracture in a Monteggia injury).
• CT or MRI scans: May be used to assess soft tissue damage (ligaments, tendons) and complex fracture patterns, especially if surgical planning is needed.

Treatment

Treatment for a radial head dislocation is more complex:

• Closed reduction: May be attempted if it is an isolated dislocation without associated fractures, but it is often more challenging than with subluxations.
• Open reduction and internal fixation (ORIF): Often required, especially if there are associated fractures (like a Monteggia fracture) or if closed reduction fails. Surgical intervention aims to realign the bones and repair damaged ligaments or fractures.
• Immobilization: Following reduction (whether closed or open), the elbow is typically immobilized in a cast or splint for several weeks to allow tissues to heal.
• Physical therapy: Essential for regaining range of motion, strength, and function after immobilization.

Prognosis and Complications

The prognosis varies depending on the severity of the injury and associated damage. Potential complications include:

• Recurrent instability: The elbow may remain unstable.
• Stiffness: Loss of full range of motion.
• Nerve damage: Especially the posterior interosseous nerve.
• Osteoarthritis: Long-term risk due to joint incongruity or trauma.
• Nonunion or malunion of fractures: If associated fractures are present.

Key Differences Summarized

When to Seek Medical Attention

Any time an individual, especially a child, experiences a sudden onset of elbow pain, refusal to use the arm, or visible deformity, prompt medical evaluation is crucial. While a radial head subluxation is generally benign and easily treated, it is impossible for a layperson to differentiate it from a more serious injury like a fracture or a complete dislocation without professional assessment. Early and accurate diagnosis is key to ensuring appropriate treatment and preventing potential long-term complications.

Conclusion

While both radial head subluxation and dislocation involve the radial head's displacement, they represent distinct injuries with different mechanisms, severities, and management strategies. Radial head subluxation is a common, relatively minor injury in children, easily corrected with a simple maneuver. Radial head dislocation, conversely, is a more severe traumatic event, often accompanied by other bone or ligamentous damage, requiring more complex medical or surgical intervention and a longer recovery period. Understanding these differences underscores the importance of proper diagnosis by a healthcare professional for any elbow injury.