Comparação da avaliação mecânica de compressão axial em seis modelos de fixadores esqueléticos externos confeccionados com barras estabilizadoras de polimetacrilato de metila ou de madeira e parafusos de aço inoxidável 304

Abstract

With the objective of testing the resistance and the biomechanical behavior of external fixators of low cost used in veterinary medicine, were created 6 prototypes la type manufactured from alternative materials, using as orthopedic implants, stainless steel screws 304 porous, and as stabilized bar the methacrylate resin or wood poles (Pinnus ellioti). The models of the fixators tested differ because they have 2, 3 or 4 implants per fractured segment. With the purpose of doing biomechanical evaluations that are closer to the real clinical situation, were selected 2 tubes of polyvinylchloride, commercially known as PVC, with 10 cm length, internal diameter of 1,27 cm and external diameter of 1,95, far 5 cm from each other, representing, this way, the bone bands and the focus of an unstable fracture. This kind of tube is like a long bone because it has an internal space that represents the medullar area and external walls that represent the two osseous cortical. To each external fixator model, were created 5 prototypes, which were submitted to mechanic tests to evaluate the axial compression strength. The device to evaluate the prototypes was the Instron model 4204, with a charge cell of 5 KN (Kilogram-Newton) and the speed of the axial compression was 2 cm/minute, according the rules ASTM D695-92. The values of rigidity, drainage point and maximum security charge were calculated, according to the methodology used by Willer et al., (1991) and by Falcão (2004). The mechanical evaluation was done in the Instituto de Macromoléculas Eloísa Mano in the Universidade Federal do Rio de Janeiro. We concluded that the models with the stabilized bar made of resin required a larger load than the models made of wood to suffer a plastic deformation. The model with 3 screws per segment of PVC tube and a resin stabilized bar showed to tolerate a higher weight than the others, before showing a plastic deformation, this way it s indicated to dogs that weight up to 26,5Kg with fractures in the thoracic limbs and for dogs that weight up to 44Kg that have fractures in the pelvic limbs.