PATHOMECHANICS OF CLOSED RUPTURE OF THE FLEXOR TENDON PULLEYS IN ROCKCLIMBERS

We performed a study on twenty-one cadaveric fingers (seven non-paired forearms) to determine the pathomechanics of closed traumatic rupture of the flexor tendon pulleys in rock climbers. The ages of the indivi duals at the time of death ranged from sixty-one to eighty-four years (mean, seventy-four years). The forearm was placed in a custom-made lo ading apparatus, and individual fingers were tested separately under s imulated in vivo loading conditions. The flexor digitorum superficiali s and profundus tendons of each digit were attached to computer-contro lled linear stepper motors that were equipped with Force transducers, and the force in the tendons was simultaneously increased until avulsi on of the tendons or osseous failure occurred, The force in the tendon s, the excursion of the tendons, and the force at the fingertip were m easured, Damage to the pulleys and bowstringing of the tendons were vi sualized with a fiberoptic camera, Two fingers fractured before comple te rupture of the pulleys, Seventeen of the remaining nineteen fingers sustained an isolated rupture of either the A2 or the A4 pulley as th e initial failure event; the A4 pulley ruptured first in fourteen digi ts (p < 0.001). The A3 and A4 pulleys ruptured simultaneously in one? finger, and the A2, A3, and A4 pulleys ruptured simultaneously in anot her. Subtle bowstringing of the flexor digitorum profundus tendon occu rred only after two consecutive pulleys had ruptured (either the A2 an d A3 pulleys or the A3 and A4 pulleys), Rupture of all three pulleys w as required to produce obvious bowstringing. Isolated rupture of the A 2 or A4 pulley did not result in detectable bowstringing of the flexor digitorum profundus tendon. The Al pulley always remained intact, CLI NICAL RELEVANCE: Bowstringing of the flexor digitorum profundus tendon across the proximal interphalangeal joint with resisted flexion of th e fingertips has been considered diagnostic for isolated closed ruptur e of the A2 pulley. The results of the present study, however, suggest that isolated injury of the A2 pulley rarely occurs. On the basis of our findings, we believe that reliance on bowstringing of the tendon a t the proximal interphalangeal joint as an indicator of an isolated ru pture of the A2 or A4 pulley may be misleading.