Mechanical evaluation of bone gap filled with rigid formulations castor oil polyurethane and chitosan in horses/Avaliacao mecanica do preenchimento de falhas osseas de equinos com formulacoes solidas de poliuretana de mamona e quitosana

Often fractures of long bones in horses are comminuted and form bone gaps, which represent a major challenge for the fixation of these fractures by loss of contact between the fragments. Bone grafts help in treating this kind of fracture and synthetic materials have been gaining ground because of the limitations of autologous and heterologous grafts. In this study were performed compressive non destructive test in 10 bones with complete cross-bone gap in mid-diaphyseal of the third metacarpal bone of horses. Using a mechanism of "crossing" the 10 bones were used in the three groups (control, castor oil poliuretane and chitosan) according to the filling material. After the test with maximum load of 1000N bone had a gap filled by another material and the test was repeated. Deformations caused on the whole bone, plate and bone tissue near and distant of gap were evaluated, using strain gauges adhered to the surface at these locations. There was a reduction in bone deformation from 14% (control) to 3,5% and 4,8% by filling the gap with Chitosan and castor oil respectively, and a reduction of strain on the plate of 96%o and 85% by filling gap with chitosan and castor respectively. An increase in intensity and direction of deformations occurred in bone near to gap after its filling; however, there was no difference in bone deformations occurring far the gap. Key words: equine, fracture, biomaterial, strenght, biomechanical test. Frequentemente, as fraturas de ossos longos nos equinos sao cominutivas, formando falhas osseas, que representam um grande desafio no momento de sua fixacao, devido a perda de contato entre os fragmentos. Os substitutos osseos sinteticos auxiliam no tratamento desse tipo de fratura. Neste estudo, foram realizados ensaios compressivos nao destrutivos em 10 ossos com falha ossea transversal completa em diafise do terceiro metacarpiano de equinos. Utilizando um mecanismo de "crossing", os 10 ossos foram utilizados nos tres grupos (controle, mamona e quitosana) de acordo com o material de preenchimento da falha. Para cada peca, realizaramse ensaios referentes aos tres grupos, com carga maxima de 1000N, por nao se tratarem de ensaios destrutivos. Foram avaliadas as deformacoes causadas no osso, na placa e no tecido osseo proximo e distante da falha, por meio de extensometros. Observou-se que houve reducao da deformacao do osso de 14% (controle) para 3,5% e 4,8%, com o preenchimento da falha com quitosana e mamona, respectivamente. Houve reduc