annular ligament

The annular ligament is a strong band of fibrous tissue that wraps around the radial head, attaching to the anterior and posterior margins of the radial notch of the ulna, forming about four-fifths of a ring (the remaining portion is the radial notch itself). It stabilizes the proximal radioulnar joint, keeping the radial head in place against the ulna while permitting rotational movement (pronation and supination) without restricting flexion/extension at the elbow. The inner surface is lined with cartilage, continuous with the articular cartilage of the radial head and radial notch, which facilitates smooth rotation. Clinically, the annular ligament is most relevant in the condition known as radial head subluxation, or 'nursemaid's elbow,' common in young children (typically ages 1-4). This occurs when a sudden longitudinal traction force is applied to the extended, pronated arm (e.g., a caregiver pulling a child's hand), causing the radial head to slip partially out from under the annular ligament, which can become interposed within the joint. Children present with a pseudo-paralysis, holding the arm slightly flexed and pronated, refusing to use it, with no visible swelling or deformity. Reduction is achieved through hyperpronation or supination-flexion maneuvers, often accompanied by a palpable/audible click, with immediate resolution of symptoms. This ligament is also a stabilizing structure assessed during elbow trauma evaluation, including radial head fractures, which can distort the ligament's integrity and mechanics.