Pathomechanics of closed rupture of the flexor tendon pulleys in rock climbers.

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 individuals 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 loading apparatus, and individual fingers were tested separately under simulated in vivo loading conditions. The flexor digitorum superficialis and profundus tendons of each digit were attached to computer-controlled linear stepper motors that were equipped with force transducers, and the force in the tendons was simultaneously increased until avulsion of the tendons or osseous failure occurred. The force in the tendons, the excursion of the tendons, and the force at the fingertip were measured. Damage to the pulleys and bowstringing of the tendons were visualized with a fiberoptic camera. Two fingers fractured before complete rupture of the pulleys. Seventeen of the remaining nineteen fingers sustained an isolated rupture of either the A2 or the A4 pulley as the initial failure event; the A4 pulley ruptured first in fourteen digits (p < 0.001). The A3 and A4 pulleys ruptured simultaneously in one finger, and the A2, A3, and A4 pulleys ruptured simultaneously in another. Subtle bowstringing of the flexor digitorum profundus tendon occurred only after two consecutive pulleys had ruptured (either the A2 and A3 pulleys or the A3 and A4 pulleys). Rupture of all three pulleys was required to produce obvious bowstringing. Isolated rupture of the A2 or A4 pulley did not result in detectable bowstringing of the flexor digitorum profundus tendon. The A1 pulley always remained intact.

Biomechanics of the thumb flexor pulley system.

The purpose of this study was to quantify the contributions of the thumb flexor pulleys on the mechanical efficiency and angular joint displacement of the human thumb. Fourteen human (below elbow) cadaveric specimens were divided into two study groups. Four experimental trials were performed with each thumb. Group 1 was tested with an intact pulley system, as well as after sequential sectioning of the oblique, A1, and A2 pulleys. Group 2 was tested with all pulleys intact and following the sequential sectioning of the (A1), oblique, and (A2) pulleys. Each forearm was mounted to a dynamic testing apparatus, and an 815 g load 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 interphalangeal and metacarpophalangeal joints. The initial sectioning of either the A1 or oblique pulley did not significantly alter the thumb efficiency or its interphalangeal or metacarpophalangeal joint angular displacement. When both the A1 and oblique pulleys were cut, significant bowstringing 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 decreased following the sectioning of both the A1 and oblique pulleys. There was no statistical difference between an isolated, intact A2 pulley and no intact pulleys. These findings indicate that repair or reconstruction of either the A1 or oblique pulley after injury will restore normal thumb kinematics.

Effects of bone ingrowth on the strength and non-invasive assessment of a coralline hydroxyapatite material.

The dependence of strength on the amount of bone growth into a hydroxyapatite material made from coral was investigated. Block and granular forms of the material were implanted into cortical and trabecular regions of the skeletons of 16 dogs. The results were examined after 4, 8, 12 and 16 wk, with four dogs in each experimental group. When implanted into cortical bone, the bending strength of the implant material was found to be highly correlated with the amount of pore space which had become occupied by bone (r = 0.92, P less than 0.005 for the block form; r = 0.84, P less than 0.005 for the granular form). Multiple regression analysis showed that six histomorphometric measures of ingrowth accounted for 96% of the variability in bending strength of the block material, and there were no significant differences between block and granular forms of the material. On the other hand, when implanted into trabecular bone, the block form of the material achieved greater compressive strength than the granular form. While both strength and ingrowth increased with time, there were poor correlations between these two variables. Finally, when the material is implanted into trabecular bone, it becomes stronger in compression than the surrounding bone; when implanted in cortical bone, linear modelling suggests that resorption and replacement of the implant would be required to approximate the bending strength of the surrounding bone.

Compression-plate fixation of acute fractures of the diaphyses of the radius and ulna.

A retrospective study was done of eighty-seven patients who had 129 diaphyseal fractures of either the radius or the ulna, or both, and who were treated with fixation using an AO dynamic-compression plate. Open fractures were internally fixed primarily, and both comminuted and open fractures routinely had bone-grafting. Ninety-eight per cent of the fractures united, and 92 per cent of the patients achieved an excellent or satisfactory functional result. The rate of infection was 2.3 per cent. Refracture occurred after removal of a 4.5-millimeter dynamic-compression plate in two patients, but there were no refractures after removal of a 3.5-millimeter plate. The 3.5-millimeter-plate system gave excellent results in patients who had a fracture of the forearm, and it minimized the risk of refracture. Our results demonstrated that immediate plate fixation of an open fracture of the forearm, with a low rate of complications, is possible.