Biomechanical comparison of the effects of circular-semicircular external fixation systems on the shear force of diaphyseal oblique tibia fractures in cats

Tibia fractures in cats are usually occured by high-rise syndrome and traffic accidents. Various methods have been described in the treatment of these fractures, such as intramedullary pin, plate, external fixation, interlocking nailing, tie-in configuration, and a combination of these treatment options. External fixation method is frequently used in human and veterinary medicine for osteosynthesis, joint stabilization and treatment of angular deformities. This method is considered more advantageous than other methods, as the configuration can be designed in multiple ways, allows wound manengement in open fractures, and causes minimal damage to the vascular structure. Although different types of this method have been defined, linear, circular and hybrid external fixation systems are frequently used. Although successful results were reported with the classical ilizarov system, human-based biomechanical analyzes revealed that the classical ilizarov system was inadequate compared to other methods in preventing shear force in oblique fractures greater than 30°. As a result of these analyzes, it is reported that a parallelogram structure should be formed in order to prevent the shear force in the best way in oblique fractures of more than 30°. Tibia bones were harvested from 20 skeletally mature cats, weighing between 3 and 6 kg, aged 1-5 years, without metabolic disorders in the skeletal system, without fractures or fissure in the tibia bones recently euthanatized for reasons unrelated to this study. Then, a 45° oblique osteotomy was performed on the coronal surface of the tibia bones with a bone saw from the middle 1/3 diaphyseal region. Biomechanical tests were performed by placing 4 different external fixation configurations on the bones. 40 bones divided into 4 groups were placed vertically in a pressure-controlled hydraulic press device and 0 N, 5 N, 10 N, 20 N, 40 N, 60 N, 100 N and 150 N axial compressions were applied, respectively. Obtained data were evaluated statistically. The aim of this study is to determine the success of circular and semicircular external fixator systems in preventing shear force in 45° oblique tibia fractures of cats. In addition, the effect of the parallelogram structure added to the configurations on the shear force is investigated. As a result, this study revealed that the circular ilizarov system prevents shear force better than the 135° semicircular arc configuration, and the parallelogram structure added to the systems increases the configuration stability to prevent shear force. It has also been shown that adding a parallelogram structure to configurations can be applied to all oblique fractures as it is very practical and increases the durability of the configuration.