Varus instability of the Elbow

Varus instability of the elbow is caused by disruption of the lateral collateral ligament complex, which includes the radial collateral ligament and lateral ulnar collateral ligament.

The lateral collateral ligamentous complex consists of the radial collateral ligament (RCL, blue), lateral ulnar collateral ligament (LUCL, pink), and the annular ligament (AL, yellow).

The radial collateral ligament (RCL, blue) originates on the lateral epicondyle and inserts on the annular ligament. Because of this attachment, injury to the radial collateral ligament may be associated with injury to the annular ligament and vice versa.

The lateral ulnar collateral ligament (LUCL, pink) originates on the lateral epicondyle, passes along the posterolateral margin of the radial head, blends with fibers of the annular ligament, and inserts on the supinator crest of the ulna (SC).

The annular ligament originates from the anterior and posterior margins of the radial notch and surrounds the radial head. It is the primary stabilizer of the proximal radioulnar joint.

The image above shows a tear of the radial collateral ligament (blue arrow) and an intact lateral ulnar collateral ligament (pink arrow). A partial tear of the common extensor tendon is also present (white arrow).

The mechanism of injury in cases of varus instability is force to the medial side of the elbow, causing compression medially and stress applied to the radial collateral ligament. The etiology is usually trauma, but chronic stress, such as from crutches, has also been implicated.

References

Chung CB. Chapter 10. In Chung CB and Steinbach LS. MRI of the Upper Extremity: Shoulder, Elbow, Wrist, and Hand. Lippincott Williams & Wilkins. 2010. pp 426-427.