Kinematic Analysis of Six Different Insertion Sites for FDS Opponensplasty.

Six variations of opponensplasty were biomechanically studied to determine if there is a significant difference in the amount of opposition produced by altering the insertion site of the tendon transfer while keeping the tendon source and pulley location constant. Five cadaveric arms were used to simulate six described insertion sites for opponensplasty tendon transfers. The arms were mounted through the ulna onto a specially designed stand. The stand was equipped with a calibrated stylus which could be turned 90° in order to accurately measure points in X, Y, and Z planes. Metacarpal-phalangeal flexion and thumb abduction were measured before and after application of a 550-g load. Axial rotation (pronation) was mathematically calculated using reference points on the thumb which were measured with the stylus before and after application of the load. The Bunnell transfer insertion site provided the greatest amount of palmar abduction, the Brand transfer insertion site the greatest metacarpophalangeal flexion, and the Royle transfer insertion site the greatest rotation. Although each of these transfers produced the greatest motion in one plane, they performed relatively poorly in the other two. The Riordan transfer insertion site into the extensor pollicis longus in line with the abductor pollicis brevis was, in our study, the overall best transfer, providing the second greatest change in motion in each of the three planes measured.