Annular Ligament of the Radius

ligamentum anulare radii

The annular ligament encircles the radial head like a collar, binding it to the ulna without restricting rotation, and forms the upper part of the superior radioulnar joint. Its funnel shape narrows distally to prevent distal displacement of the radial head. In children under 5 the radial head is not yet fully developed and can be pulled through the annular ligament by a sudden traction force, producing a nursemaid elbow (pulled elbow) where the ligament becomes trapped in the joint.

Region: Upper Arm

Anatomical Data

Origin, Insertion & Supply

Origin	Anterior margin of the radial notch of the ulna
Insertion	Posterior margin of the radial notch of the ulna, encircling the radial head

Biomechanics

Function & Actions

Actions	Holds the radial head in the radial notch of the ulna; allows free forearm rotation while preventing radial head escape

Clinical Relevance

Clinical Notes

Nursemaid elbow is the most common elbow injury in children under 5, produced by a sudden longitudinal traction force on the extended elbow such as when lifting a child by the wrist. The child holds the arm pronated and refuses to use it but has no swelling or bony tenderness. Reduction is achieved by hyperpronation or supination-flexion manoeuvres that allow the ligament to slip back into position, producing an immediate return of normal arm use.

Pathology

Common Injuries & Conditions

Nursemaid Elbow

Radial head subluxation through the annular ligament in children under 5 from a sudden traction force, producing a pronated held arm without bony tenderness, reduced by the hyperpronation or supination-flexion technique with immediate resolution.