Histology and arthroscopic anatomy of the ulnar collateral ligament of the elbow.

The histology and arthroscopic anatomy of the ulnar collateral ligament of the elbow were studied in cadaveric specimens. The capsule consists of two layers of collagen fibers, with two distinct ligamentous bundles corresponding to anterior and posterior portions of the ulnar collateral ligament. The posterior bundle consists of distinct collagen bundles within the layers of the capsule; the anterior bundle consists of a similar thickening within the capsular layers, with an additional ligament complex superficial to the capsular layers. With arthroscopy only the anterior 20% to 30% of the anterior bundle of the ulnar collateral ligament could be visualized via the anterior portal. Only the posterior 30% to 50% of the posterior bundle could be seen via the posterior portals. After sectioning of the anterior bundle, joint instability was noted arthroscopically by an increased opening in the ulnohumeral joint with application of valgus stress. At arthroscopy ulnar collateral ligament tears may be visualized in part or not at all. To diagnose a tear or laxity in the ulnar collateral ligament, a demonstration of an increase in the opening of the ulnohumeral joint in response to valgus stress is useful.