The effects of transection and reconstruction of the ulnar collateral ligament complex on the position of the proximal phalanx of the thumb during simulated tip pinch

Injuries to the ulnar collateral ligament (UCL) of the metacarpophalangeal joint of the thumb are common and may result in functional instability of t he joint. Eight cadaveric hands were studied. Physiologic levels of muscle loads were applied to the extrinsic flexor tendon of the thumb to simulate tip pinch of the thumb. We investigated the effects of transection of the U CL and accessory UCL (UCL complex) with and without transection of the dors al capsule and volar plate and of reconstruction of the UCL, for 2 surgical techniques, on the position of the proximal phalanx with respect to the th umb metacarpal. The spatial positions of the metacarpal and proximal phalan x were measured with a 6 degrees of freedom digitizing system for flexion a ngles from 0 degrees to 60 degrees in 15 degrees increments. Transection of the UCL complex, dorsal capsule, and volar plate (ulnar capsuloligamentous structures) of the metacarpophalangeal joint did not affect radioulnar dev iation or radioulnar shift, but did produce significant increases in supina tion by 8 degrees and volar translation by 2 mm at 45 degrees and 60 degree s compared with those found for the intact joint. The UCL was reconstructed with a tendon graft using the autogenous extensor digiti quinti. The first surgical technique, a traditional technique, and the second surgical techn ique, a technique based on anatomy, returned the position of the proximal p halanx on the metacarpal head to normal, with the exceptions of volar trans lation of the proximal phalanx at 60 degrees and trends toward abnormal sup ination of the proximal phalanx for flexion angels of 45 degrees and 60 deg rees. (J Hand Surg 2000;25A:313-321. Copyright (R) 2000 by the American Soc iety for Surgery of the Hand.).