Injuries of the ulnar collateral ligament of the thumb metacarpophalangeal joint. Biomechanical and prospective clinical studies on the usefulness of valgus stress testing.

In an effort to determine whether valgus stress testing of the thumb metacarpophalangeal joint is predictive of a torn and displaced ulnar collateral ligament, anatomic and prospective clinical studies were performed and the results correlated. In the anatomic study on autopsy specimens, dividing the proper collateral ligament resulted in a significant increase in valgus instability of the flexed metacarpophalangeal joint. Significantly less laxity was noted when the joint was tested in extension. When the accessory collateral ligament/palmar plate complex was also divided, valgus instability in extension increased to the extent that it no longer differed significantly from the values obtained when the joint was tested in 30 degrees flexion. In the clinical study, valgus instability of greater than 35 degrees when the joint was positioned in extension and then stressed consistently indicated the presence of tears of the proper and accessory collateral ligaments: A Stener's lesion was present in 15 of 17 such cases (87%). Values on valgus stress testing of the metacarpophalangeal joint in extension and 30 degrees flexion are highly predictive of both disruption and displacement of the ulnar collateral ligament of the thumb.