Radial Head Dislocations: Types, Causes, and Complex Injuries

What are the different types of radial head dislocations?

Radial head dislocations, injuries affecting the elbow joint, are primarily categorized by the direction of displacement of the radial head relative to the capitellum and its association with other bone or ligamentous injuries, ranging from isolated occurrences to complex fracture-dislocations.

Understanding the Radial Head and Elbow Joint

The radial head is the proximal (upper) end of the radius bone, one of the two long bones of the forearm. It articulates with the capitellum of the humerus (upper arm bone) and the radial notch of the ulna (the other forearm bone), forming part of the elbow joint. This articulation, stabilized by the annular ligament which encircles the radial head, is crucial for forearm rotation (pronation and supination) and elbow flexion/extension. A radial head dislocation occurs when the radial head is displaced from its normal articulation, disrupting the joint's integrity and function.

Isolated Radial Head Dislocations

These dislocations occur when the radial head displaces without an associated fracture of the ulna. They are relatively uncommon in adults but can occur due to direct trauma or a fall onto an outstretched hand (FOOSH) with a rotational component.

• Anterior Dislocation: This is the most frequent type of isolated radial head dislocation. The radial head displaces anteriorly (forward) relative to the capitellum. It often results from a FOOSH injury where the forearm is pronated and the elbow is extended, causing the radial head to be levered forward.
• Posterior Dislocation: Less common than anterior dislocations, here the radial head displaces posteriorly (backward). This can occur from a direct blow to the elbow or a FOOSH injury with the elbow in flexion.
• Lateral or Medial Dislocation: These are rare and typically indicate severe trauma, often accompanied by other significant soft tissue or bony injuries around the elbow, as the radial head displaces to the side.

Nursemaid's Elbow (Pulled Elbow)

This is a very common injury in young children, typically between 1 and 4 years of age. It is technically a subluxation (partial dislocation) rather than a complete dislocation of the radial head.

• Mechanism: It occurs when a sudden traction force is applied to the child's extended and pronated arm, often when an adult pulls a child up by the hand or wrist, or swings them. This sudden pull causes the annular ligament to slip over the radial head and become entrapped in the joint.
• Presentation: The child typically presents with pain and refuses to use the affected arm, holding it close to the body with the elbow slightly flexed and the forearm pronated. There is usually no swelling or deformity.
• Treatment: Reduction is typically simple and non-surgical, involving specific maneuvers by a healthcare professional that release the entrapped ligament.

Monteggia Fracture-Dislocation

The Monteggia fracture-dislocation is a complex injury involving a fracture of the ulna bone accompanied by a dislocation of the radial head. It is a critical injury because the radial head dislocation often goes unrecognized if only the ulnar fracture is addressed.

• Classification (Bado Classification): This widely used system categorizes Monteggia injuries based on the direction of the radial head dislocation and the ulnar fracture location/angulation:
  • Type I: Anterior dislocation of the radial head with an anteriorly angulated fracture of the ulnar diaphysis (shaft). This is the most common type, often caused by hyperextension injuries.
  • Type II: Posterior or posterolateral dislocation of the radial head with a posteriorly angulated fracture of the ulnar diaphysis. This is less common and results from direct trauma or hyperflexion.
  • Type III: Lateral or anterolateral dislocation of the radial head with a fracture of the ulnar metaphysis (near the joint). This often occurs in children due to abduction forces.
  • Type IV: Anterior dislocation of the radial head with fractures of both the ulna and radius at the same level. This is the least common and most severe type.

Essex-Lopresti Lesion

This is another severe and often missed injury pattern that involves the radial head. It is characterized by a fracture of the radial head (not just a dislocation), combined with a disruption of the distal radioulnar joint (DRUJ) at the wrist and an interosseous membrane tear (the strong fibrous sheet connecting the radius and ulna along their length).

• Mechanism: Typically results from a high-energy fall onto an outstretched hand, transmitting axial forces up the forearm.
• Significance: The interosseous membrane tear allows for axial instability, causing the radius to migrate proximally (upwards), leading to the DRUJ disruption at the wrist. If the DRUJ injury is not recognized and treated, chronic wrist pain, instability, and forearm dysfunction can result.

Clinical Significance and Management

Accurate diagnosis of the specific type of radial head dislocation is paramount for appropriate treatment and optimal recovery. Misdiagnosis or delayed treatment, especially in complex fracture-dislocations like Monteggia or Essex-Lopresti lesions, can lead to chronic pain, instability, reduced range of motion, and long-term functional impairment of the elbow and/or wrist. Management typically involves reduction of the dislocation, often followed by immobilization, and for complex injuries, surgical fixation of fractures and reconstruction of ligaments may be necessary.

Rehabilitation Considerations

Following the acute management, a structured rehabilitation program is crucial. This typically involves:

• Pain and Swelling Management: Initial focus on reducing discomfort.
• Restoration of Range of Motion: Gentle, progressive exercises to regain elbow and forearm movement.
• Strengthening: Gradual progression of exercises to rebuild strength in the forearm, elbow, and shoulder muscles.
• Proprioception and Stability Training: Exercises to improve joint awareness and dynamic stability.

Understanding the specific type of radial head dislocation informs the entire treatment and rehabilitation process, highlighting the intricate biomechanics of the elbow and forearm.