BIOMECHANICS OF THE THUMB FLEXOR PULLEY SYSTEM

The purpose of this study was to quantify the contributions of the thu mb flexor pulleys on the mechanical efficiency and angular joint displ acement of the human thumb. Fourteen human (below elbow) cadaveric spe cimens were divided into two study groups. Four experimental trials we re performed with each thumb. Group 1 was tested with an intact pulley system, as well as after sequential sectioning of the oblique, A1, an d A2 pulleys. Group 2 was tested with all pulleys intact and following the sequential sectioning of the (A1), oblique, and (A2) pulleys. Eac h forearm was mounted to a dynamic testing apparatus, and an 815 g loa d was applied at the thumb tip. The flexor pollicus longus tendon was attached to a force transducer and computer-driven stepper motor, and tension was recorded through full range of motion of the interphalange al and metacarpophalangeal joints. The initial sectioning of either th e A1 or oblique pulley did not significantly alter the thumb efficienc y or its interphalangeal or metacarpophalangeal joint angular displace ment. When both the A1 and oblique pulleys were cut, significant bowst ringing was observed, as well as decreased interphalangeal flexion and increased metacarpophalangeal flexion; total angular motion remained unchanged. The tension required to achieve a given displacement also d ecreased following the sectioning of both the A1 and oblique pulleys. There was no statistical difference between an isolated, intact A2 pul ley and no intact pulleys. These findings indicate that repair or reco nstruction of either the A1 or oblique pulley after injury will restor e normal thumb kinematics.