Undersurface tear of the ulnar collateral ligament in baseball players. A newly recognized lesion.

Seven patients were diagnosed with an undersurface tear of the deep capsular layer of the anterior bundle of the ulnar collateral ligament. Preoperatively, all of the patients had tenderness over the anterior bundle of the ulnar collateral ligament and pain with valgus stressing of the elbow. Six of the seven patients had a normal magnetic resonance imaging scan, with one magnetic resonance imaging scan showing degeneration within the ligament. All of the patients had a negative computed tomography arthrogram for extracapsular contrast extravasation. A consistent finding in five of the seven patients was a leak of contrast around the edge of the humerus or ulna, although the contrast was contained within the joint. At arthroscopic evaluation, all of the patients demonstrated medial elbow instability as valgus stress was applied across the elbow joint in 70 degrees of flexion. All of the patients underwent open medial elbow surgery, where the ulnar collateral ligament was visualized and found to be intact externally. But when the anterior bundle was incised, there was a detachment of the undersurface of the ligament at the ulna or the humerus. Cadaveric dissections were performed to define the anatomy of the insertion sites and to confirm that this lesion was not an anatomic variant. A tear of the deep layer of the ulnar collateral ligament can result in symptomatic instability that is difficult to diagnose with conventional preoperative testing. This lesion of the anterior bundle of the ulnar collateral ligament has not been previously reported, and in our series it was associated with persistent medial elbow pain in throwing athletes.