The annular ligament is a strong, fibrous band of connective tissue found within the complex structure of the elbow joint. It is a fundamental component of the elbow’s lateral ligamentous complex, providing static stability to the joint. This specialized ligament connects bones while permitting necessary movement, functioning much like a biological strap. Its integrity is essential for the proper mechanics of the forearm and elbow.
Where the Annular Ligament is Located
This ligament forms a ring-like structure, or cuff, situated specifically around the head of the radius bone at the elbow. It is securely anchored to the ulna, one of the two forearm bones. The annular ligament originates from the anterior margin of the radial notch on the ulna and inserts on the posterior margin of the same notch. This attachment creates a fibro-osseous circle, wrapping tightly around approximately four-fifths of the radial head’s circumference. This circular band holds the radial head against the ulna, allowing the radius to spin freely within the cuff.
The Ligament’s Role in Elbow Stability
The primary function of the annular ligament is to stabilize the proximal radioulnar joint, the articulation between the radius and the ulna near the elbow. This structure maintains the connection between these two bones, preventing the radial head from slipping out of its socket in the ulna. The ligament allows for pronation and supination, the actions of turning the palm downward and upward, as the radial head rotates within the fibrous ring.
Understanding Radial Head Subluxation
Radial head subluxation, commonly known as Nursemaid’s Elbow or Pulled Elbow, is the most frequent injury involving the annular ligament in children. This partial dislocation occurs when the head of the radius slips slightly out of the annular ligament’s grasp. The injury happens because the ligament is relatively loose and less developed in young children, making it more easily displaced. The peak incidence is between one and four years of age, and the condition is uncommon after the child reaches five or six years old.
The injury mechanism involves a sudden, strong axial traction or pulling force applied to a child’s extended arm. This often occurs when an adult abruptly lifts or swings a child by the hands or forearms. Less forceful actions, such as pulling a child’s arm through a sleeve while dressing, can also cause the injury. The tug causes the radial head to move distally, and a portion of the annular ligament can become momentarily trapped between the radial head and the humerus. This entrapment causes immediate pain and prevents proper joint function.
A child who sustains this injury will cry out suddenly and refuse to use the injured arm. They hold the arm limp at their side, often slightly bent and with the palm turned down. There is usually no visible swelling or deformity at the elbow, which can sometimes confuse parents. Immediate medical attention is necessary for a prompt diagnosis and treatment. Treatment involves a quick, specific maneuver performed by a healthcare professional to gently release the trapped ligament and return the radial head to its normal position.