Annular ligament of the elbow

The annular ligament is a part of the lateral collateral ligamentous complex of the elbow joint and a major stabilizer of the proximal radioulnar joint.

Gross anatomy

The annular ligament is located within the elbow joint and is one of four ligaments forming the lateral collateral ligamentous complex of the elbow ^1,2. It creates a loop around the radial head attaching it to the radial notch of the proximal ulna, tapering distally in a funnel-shaped manner as it spreads over the proximal part of the radial neck ¹. It consists of superior and inferior obliques bands and a capsular layer ³.

Function

Its anterior portion serves as a distal insertion site for the radial collateral ligament ^1-3.

Together with the interosseous membrane of the forearm the annular ligament stabilizes the proximal radioulnar joint and holds the radial head in the ulnar sigmoid notch during forearm pronation and supination ¹.

Attachments

The annular ligament features an anterior and posterior attachment to the ulnar sigmoid notch ^1,2. The posterior attachment might be fenestrated and is located proximal to the distal insertion site of the lateral ulnar collateral ligament and the supinator tubercle ².

Relations

Posteriorly the annular ligament blends with fibers of the lateral ulnar collateral ligament ¹.

At its superior rim, it might be bordered by synovial folds that extend into the radiocapitellar joint which might be variably present ¹.

Radiographic features

Ultrasound

The annular radial collateral ligament can be seen as a hyperechoic structure on ultrasound.

MRI

The annular ligament can be easily identified on MRI on axial and sagittal images as a band-like structure with a homogeneously low-signal intensity encircling the radial head ^1,2.

Related pathology

Pathologies associated with the annular ligament include the following ^1,2:

• Monteggia fracture-dislocation
• nursemaid elbow
• radial head fractures
• elbow dislocation
• radial head instability