Nursemaid's Elbow: Understanding Radial Head Subluxation and Annular Ligament Displacement

What is Subluxation of the Radial Head and Displacement of the Annular Ligament?

This condition, commonly known as "Nursemaid's Elbow" or "Pulled Elbow," occurs when the radial head (the top of the forearm bone) partially slips out from under the annular ligament, which normally holds it in place, often due to a sudden longitudinal pull on the forearm.

Understanding the Anatomy of the Elbow Joint

To fully grasp subluxation of the radial head and displacement of the annular ligament, it's essential to understand the specific anatomy of the elbow joint, particularly the unique relationship between the radius and the ulna, and the critical role of surrounding ligaments.

• The Humerus: This is the large bone of the upper arm, forming the top part of the elbow joint.
• The Ulna: This is one of the two bones of the forearm, forming the main hinge joint with the humerus and providing stability.
• The Radius: The other bone of the forearm, located on the thumb side. Its upper end, the radial head, is shaped like a disc and articulates with both the humerus and the ulna, allowing for rotation of the forearm (pronation and supination).
• The Annular Ligament: This is a strong, fibrous band of connective tissue that encircles the radial head, holding it snugly against the ulna. It acts like a collar, stabilizing the radial head while still allowing it to pivot during forearm rotation.

In young children, the radial head is not yet fully developed and is relatively smaller compared to the adult radial head. The annular ligament in children is also more lax and pliable, making it more susceptible to displacement.

What is Subluxation of the Radial Head?

Subluxation refers to a partial or incomplete dislocation of a joint, where the bone is displaced from its normal articulation but still maintains some contact. In the context of the radial head:

• Definition: Subluxation of the radial head specifically means that the radial head partially slips out of the confines of the annular ligament. It does not completely dislocate from the elbow joint, but its normal anatomical alignment is disrupted.
• Mechanism of Injury: This injury most commonly occurs due to a sudden, forceful pull on an extended arm, often when the forearm is pronated (palm facing down or backward). Examples include:
  • Pulling a child up by the hand or wrist.
  • Swinging a child by their arms.
  • Jerking a child's arm to prevent a fall.
  • Even turning over in a crib awkwardly.
• Prevalence: While it can technically occur at any age, it is overwhelmingly common in children between 1 and 4 years old, peaking around 2 to 3 years. This is due to the relative laxity of the annular ligament and the smaller, less developed radial head in this age group.

What is Displacement of the Annular Ligament?

The displacement of the annular ligament is the direct anatomical consequence that enables the radial head subluxation:

• Role of the Ligament: The annular ligament's primary function is to keep the radial head pressed against the ulna, ensuring smooth rotation.
• Mechanism of Displacement: When a sudden traction force is applied to the forearm, especially with the elbow extended and the forearm pronated, the radial head can be pulled distally. If the force is sufficient, the annular ligament can slip or "displace" over the radial head and become trapped between the radial head and the capitellum of the humerus (the part of the humerus that articulates with the radial head) or between the radial head and the ulna.
• Result: With the ligament no longer properly encircling the radial head, the radial head is no longer held securely in place, leading to its subluxation. This entrapment of the ligament is what prevents the radial head from easily returning to its normal position without intervention.

Causes and Risk Factors

The primary cause is a traction injury to the extended and pronated arm. Specific risk factors include:

• Age: Children aged 1-4 years are most vulnerable due to their developing bones and ligaments.
• Ligamentous Laxity: The ligaments in young children are more elastic and less robust than in adults.
• Anatomical Proportions: The radial head is relatively smaller in young children, making it easier for the annular ligament to slip over it.
• Caregiver Actions: Any activity involving a sudden pull on a child's arm, such as:
  • Lifting a child by one hand.
  • Swinging a child by the arms.
  • Pulling a child to hurry them along.
  • Catching a child by the arm during a fall.

Recognizing the Signs and Symptoms

The presentation of Nursemaid's Elbow is often quite characteristic:

• Immediate Pain (Often Transient): While there may be a brief cry of pain at the moment of injury, severe pain often subsides quickly.
• Refusal to Use the Arm: The most classic sign is the child's reluctance or complete refusal to use the affected arm. They typically hold the arm still, close to the body, with the elbow slightly bent and the forearm pronated (palm turned inward/downward).
• No Visible Deformity or Swelling: Unlike a fracture or full dislocation, there is usually no obvious swelling, bruising, or deformity around the elbow joint.
• Distress: The child may be anxious, upset, or cry when attempts are made to move the arm.
• Limited Movement: Attempts to supinate (turn the palm up) or extend the elbow will be met with resistance and pain.

Diagnosis

Diagnosis is primarily clinical, based on the history of injury and the physical examination:

• History: A clear history of a sudden pull on the arm, followed by the child's refusal to use it, is highly suggestive.
• Physical Examination: The clinician will observe the child's arm posture and gently attempt to elicit movement. Given the characteristic presentation, further diagnostic tests are often unnecessary.
• Imaging (X-rays): X-rays are usually normal in cases of Nursemaid's Elbow because it is a ligamentous injury, not a bone fracture. They are typically only performed if there is suspicion of a fracture (e.g., a fall directly onto the elbow, significant swelling, or an atypical mechanism of injury) or if the diagnosis is unclear.

Treatment and Reduction

The treatment for subluxation of the radial head is a manual procedure known as reduction, which aims to reposition the radial head back into its normal anatomical alignment within the annular ligament. This is a quick and effective procedure, typically performed by a healthcare professional.

• Manual Reduction Techniques: Two common methods are used:
  • Supination-Flexion Method: The examiner holds the child's arm at the elbow, applies gentle pressure over the radial head, then supinates the forearm (turns the palm up) while simultaneously flexing the elbow. A subtle "click" or "clunk" may be felt as the radial head pops back into place.
  • Hyperpronation Method: The examiner holds the child's arm at the elbow, stabilizes the humerus, and then forcefully hyperpronates the forearm (turns the palm even further downward). This method is often preferred for its slightly higher success rate and can be less distressing for the child. A click may also be felt.
• Immediate Relief: Once successfully reduced, the relief is almost immediate. The child will typically begin using the arm within minutes, often surprising parents with the rapid recovery.
• Post-Reduction Care: No immobilization is usually required. Parents are advised to observe the child and educate them on preventing recurrence.

Prevention Strategies

Prevention is key, especially for children prone to recurrence:

• Educate Caregivers: Inform parents, grandparents, and other caregivers about the mechanism of injury.
• Avoid Traction on the Arm:
  • Do not pull a child up by their hands or wrists.
  • Do not swing children by their arms.
  • When lifting, lift from under the armpits or around the torso.
  • When guiding a child, hold their hand, but avoid jerking or pulling.

Long-Term Outlook and Recurrence

The prognosis for Nursemaid's Elbow is excellent with proper and timely reduction. There are typically no long-term complications or functional deficits.

• Recurrence: It is not uncommon for a child to experience recurrence, especially if they have had one episode. The annular ligament may remain somewhat stretched after the initial injury, making it easier to sublux again.
• Age and Maturation: As children grow older (typically after age 4-5), the radial head develops and enlarges, and the annular ligament strengthens and becomes less pliable. This naturally reduces the risk of recurrence significantly.
• No Lasting Damage: Provided the subluxation is reduced promptly, there is no lasting damage to the joint or ligament.