ABSTRACT
BACKGROUND: Many conservative and surgical techniques for mallet finger have been described. Most of them have reached an agreement, but the fixation of the proximal interphalangeal joint has not reached a consensus. OBJECTIVE: To discuss the effect of proximal interphalangeal joint motion on the tension of the zone I extensor tendon and to search the fixation position of proximal interphalangeal joint at the minimum tension of the zone I extensor tendon through measuring extensor tendon so as to provide reference for selecting optimal fixation position in the treatment of mallet finger. METHODS: The maximal passive flexion angles of the distal interphalangeal joint of the index, middle, ring and little fingers were measured in 20 cadaver hands when the proximal interphalangeal joint flexed at 0°, 20°, 40°, 60°, 80° and 100°. An incision was made over the back of the distal interphalangeal joint to expose the zone I extensor tendon. The extensor tendon was incised laterally at the level of the distal interphalangeal joint with the distal interphalangeal joint fixed in extension position to make a mallet finger. A Kirschner wire was used to pierce through and perpendicular to the distal phalangeal basement as a sign. Paralleling to this sign, the zone I extensor tendon was marked and its relative distance to the sign was measured as the sliding distance of the extensor. The widest gap between the tendon edges and the tendon sliding distance were recorded, while the proximal interphalangeal joint was in extension and 20°, 40°, 60°, 80° and 100° flexion positions. RESULTS AND CONCLUSION: (1) The maximal passive flexion angle of the distal interphalangeal joint increased with the proximal interphalangeal joint flexion increased. (2) The gap between the extensor tendon edges in zone I reduced when the angle of proximal interphalangeal joint increased. The proximal extensor tendon gliding distance increased, while the proximal interphalangeal joint flexion increased. The gap between the extensor tendon edges in zone I was (1.322 8±1.0788 9) mm when the proximal interphalangeal joint was in extension position. The proximal extensor tendon glided distally, when the proximal interphalangeal joint flexed to 100° with an average sliding distance of (1.540 5±0.690 70) mm. (3) The zone I extensor tendon has the maximal tension while the proximal interphalangeal joint is in extension position. The tension in the zone I extensor tendon reduced when the angle of proximal interphalangeal joint increased. The tension in the zone I extensor tendon was minimal when the proximal interphalangeal joint flexed to 100°.