Imaging description

Medical imaging assessment of the integrity of the ulnar collateral ligament (UCL) is best performed using MR arthrography of the elbow. The ulnar collateral ligament consists of three bundles: anterior, transverse, and posterior. Clinically significant tears of the UCL involve the anterior bundle since the anterior bundle is the primary restraint to valgus force on the elbow from 20° to 120° of flexion. This bundle is best seen on coronally oriented MR images. When normal, it is seen as a uniformly low-signal intensity band extending from the base of the medial epicondyle to the medial aspect of the coronoid process (known as the sublime tubercle) (Figure 23.1). A normal subligamentous recess is seen between the medial surface of the trochlea and the undersurface of the anterior bundle of the UCL on elbow MR arthrography; however, the insertion of the anterior bundle on the sublime tubercle should be tight with no visible recess between the coronoid process and the UCL in young adults without ligamentous degeneration (Figure 23.2). A full thickness tear of the anterior bundle of the UCL is demonstrated by disruption of the fibers with abnormal insinuation of contrast into the tear (Figure 23.3). Full thickness tears most commonly occur in the midsubstance of the anterior bundle; however, avulsions at the epicondylar or tubercle attachments can occur.

Importance

Full thickness tears need to be identified by MR arthrography as the physical exam diagnosis of ruptures of the anterior bundle of the UCL can sometimes be difficult. If missed, this can cause an increase in patient morbidity due to a delay in diagnosis and definitive surgical treatment.