Avaliação das propriedades mecânicas de diferentes modelos de fixadores esqueléticos externos tipo Ib de baixo custo

Abstract

Six different frames of low cost external skeletal fixators used in veterinary orthopedics were submitted to mechanical evaluation of the axial compression. The apparatuses were separated in two different models, one with wooden connection bars (Pinnus ellioti) and another with PMMA (polymethylmethacrylate) connection bars. Tubes of polyvynil chloride (PVC) were used to simulate the bone model. Each model were respresented by frames elaborated in typo Ib configuration, with eight insertion pins (four per fragment/ two per connection bar in each fragment), 12 insertion pins (six per fragment/ three per connections in each fragment) and 16 insertion pins (eight per fragment/ four per connection bar in each fragment). We have employed a universal essay machine, model 4204, Instron, at a two cm/min speed to submit the models to axial compression force tests and thus calculate their stiffness, safety load and yield point. Within the results, stiffness increase with a higher number of insertion pins; significant difference between the two models of connection bars is not detected. Otherwise the strength necessary to promote a one milimeter displacement at the fracture gap (safety load) is higher at the wooden connection bars apparatuses; this value also increases if the number of fixation pins is elevated, except if we compare frames with 12 insertion pins (six per fragment/ three per connections in each fragment) and 16 insertion pins (eight per fragment/ four per connection bar in each fragment). The strength necessary to promote a permanent deformation at the apparatuses (yield point) do not show significant statistic difference.