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 m etacarpophalangeal joint is predictive of a torn and displaced ulnar c ollateral ligament, anatomic and prospective clinical studies were per formed and the results correlated. In the anatomic study on autopsy sp ecimens, dividing the proper collateral ligament resulted in a signifi cant increase in valgus instability of the flexed metacarpophalangeal joint. Significantly less laxity was noted when the joint was tested i n extension. When the accessory collateral ligament/palmar plate compl ex was also divided, valgus instability in extension increased to the extent that it no longer differed significantly from the values obtain ed when the joint was tested in 30-degrees flexion. In the clinical st udy, valgus instability of greater than 35-degrees when the joint was positioned in extension and then stressed consistently indicated the p resence of tears of the proper and accessory collateral ligaments: A S tener's lesion was present in 15 of 17 such cases (87%). Values on val gus stress testing of the metacarpophalangeal joint in extension and 3 0-degrees flexion are highly predictive of both disruption and displac ement of the ulnar collateral ligament of the thumb.