Effects of reconstructed radial collateral ligament on index finger mechanics.

Twenty fresh frozen hand specimens from cadavers were studied. Physiologic levels of extrinsic muscle loads were applied to the extrinsic flexor tendons of the index finger to simulate tip pinch of the finger on a fixed plate. The acute effects of transection of the radial collateral ligament and accessory radial collateral ligament (radial collateral ligament complex) with and without transection of the dorsal capsule and volar plate on the position of the proximal phalanx with respect to the metacarpal bone of the index finger were investigated. The acute effects of reconstruction of the radial collateral ligament, for each of two different surgical techniques, on the position of the proximal phalanx also were investigated. The spatial positions of the metacarpal bone and proximal phalanx were measured with a six-degree-of-freedom digitizing system for flexion angles from 0 degrees to 90 degrees in increments of 15 degrees. Transection of the radial collateral ligament complex resulted in significant increases in ulnar deviation (adduction) of the proximal phalanx and in volar translation. Additional transection of the dorsal capsule and volar plate caused significant increases in ulnar deviation, pronation, volar translation, and ulnar shift. The first surgical technique, one traditionally used to reconstruct the metacarpophalangeal joint of the thumb, failed to return the three-dimensional position of the proximal phalanx on the metacarpal head of the index finger to normal. The second surgical technique, based on anatomy, returned the position of the proximal phalanx to levels not statistically different from normal for most flexion angles.