A biomechanical strength comparison of external fixators.

BACKGROUND: The purpose of this study was to biomechanically test the current commercially available uniplanar, half-pin external fixators, comparing stiffness, weight, and cost. METHODS: The Hammer, HexFix, Hoffmann, Monotube Blue, Monotube Red, Torus, TraumaFix, and Ultra-X were tested using previously published methods. The Instron 4500 was used to assess the strength characteristics in axial, torsional, anteroposterior, and lateral bending of each device. Weight was based on the unassembled fixator construct. Cost was determined from the purchase price of each individual fixator. RESULTS: The results of this study revealed that the Torus was the stiffest external fixator tested in torsion. The Monotube Red was the stiffest in axial loading, anteroposterior bending, and lateral bending. The Hammer and Hoffmann external fixators were the heaviest constructs. The Torus and HexFix were the most expensive. CONCLUSION: Many factors, including stiffness, weight, cost, ease of application, fracture characteristics, and personal preference, go into deciding which external fixator to use. The data presented compare stiffness characteristics of several fixators under standardized loading conditions. These data indicate that the Torus and Monotube Red provide the greatest stiffness when comparing all modes of failure.

Drug interactions and vasoconstrictors used in local anesthetic solutions.

This study examined widely advertised interactions between sympathomimetic amine vasoconstrictors currently used in dental local anesthetic solutions and MAO inhibitors (phenelzine, 5 mg/kg), phenothiazines (chlorpromazine, 2 mg/kg), and tricyclic antidepressants (desipramine, 2 mg/kg). Twelve greyhound dogs premedicated with morphine and anesthetized with urethane and alpha-chloralose were prepared for physiologic recordings. During a control period, the dogs received bolus injections of epinephrine, norepinephrine, and levonordefrin sufficient to construct log-linear dose-response curves for each agent. Commercial anesthetic solutions, with and without the vasoconstrictors, were also used. The dose-response curves were then reproduced 1 hour after the administration of a drug interactant. Cardiovascular responses were not influenced by the coadministration of local anesthetics or by the prior administration of phenelzine. Chlorpromazine ameliorated pressor responses to norepinephrine and levonordephrin and reversed the hypertensive effect of high-dose epinephrine. Desipramine significantly increased vasoconstrictor potencies, particularly those of levonordefrin and norepinephrine, which were multiplied more than sixfold.