The annular ligament of the radius is a pivotal structure surrounding the head of the radius. This ligament ensures the proper articulation of the radius with the ulna, playing a fundamental role in the movement and stability of the proximal radioulnar joint. Its name, “annular,” is derived from its ring-like shape.
Location
The annular ligament encircles the head of the radius, binding it to the radial notch of the ulna. This makes it an integral part of the proximal radioulnar joint.
Structure
The annular ligament is a strong, fibrous band that forms almost a complete circle. Its anterior and posterior margins are fused with the lateral and medial borders of the radial notch of the ulna. The ligament is broader anteriorly and posteriorly while being thinner on its sides. The superior surface of this ligament interacts with the radial head, while the inferior surface is attached to the neck of the radius.
Function
- Stabilization of the Radius: The primary role of the annular ligament is to maintain the head of the radius in contact with the radial notch of the ulna. This keeps the bone securely in place during forearm rotations.
- Allowance of Rotation: While the annular ligament stabilizes the radial head, it also permits it to rotate freely within its collar. This rotation is pivotal for the pronation (turning the palm downward) and supination (turning the palm upward) movements of the forearm.
- Joint Congruency Maintenance: By ensuring the radius and ulna articulate correctly, the annular ligament aids in maintaining the overall congruency of the elbow and proximal radioulnar joints.
Clinical Significance
- Nursemaid’s Elbow: One of the most common injuries associated with the annular ligament is “nursemaid’s elbow” or radial head subluxation. This occurs predominantly in young children when an abrupt pulling force is applied to the extended forearm, causing the radial head to slip out from under the annular ligament. Symptoms include pain and the refusal to use the affected arm. Fortunately, this injury is easily treated by a clinician through a gentle maneuver to relocate the radial head.
- Trauma: Direct blows or trauma to the elbow can lead to annular ligament tears or disruptions. These might necessitate medical intervention, especially if associated with radial head dislocations.
- Diagnostic Modalities: In cases of suspected annular ligament injuries, X-rays are typically the first-line diagnostic tool. However, MRI may be used to visualize soft tissue injuries more clearly.
- Treatment: Besides the manual reduction for nursemaid’s elbow, significant annular ligament injuries might require immobilization, physical therapy, or in rare cases, surgical intervention.
