Anterior versus modified combined instrumentation for burst fractures of the thoracolumbar spine: a biomechanical study in calves.

PURPOSE To compare stability after anterior instrumentation alone versus modified combined anterior and posterior instrumentation for burst fractures of the thoracolumbar spine in calves. METHODS Thoracolumbar spines of 10 calves were used. An axial compression force was applied on each specimen using a material-testing machine, until there was a burst fracture at T12 or L1. Five specimens were fixed with anterior instrumentation alone, using 2 rods connected by 2 screws above and 2 screws below the fractured vertebra plus one tranverse connector. Another 5 were fixed with our modified technique of combined anterior and posterior instrumentation. This entailed one rod connected with one screw above and one screw below the fractured vertebra anteriorly, and another rod connected with one transpedicular screw above and one transpedicular screw below the fractured vertebra posteriorly. After instrumentation, the experiment was conducted again on each specimen and the compressive stiffness and vertebral height loss between the 2 groups compared. RESULTS The mean compressive stiffness was significantly greater after modified combined anterior and posterior instrumentation than anterior instrumentation alone (5508 vs 2888 N, p=0.0256), whereas the respective vertebral height losses were 37 and 33 mm (p=0.3808). CONCLUSION Our modified technique of combined anterior and posterior instrumentation provides greater stability than traditional anterior instrumentation alone.