Finite element analysis of the indirect reduction of posterior pedicle screw fixation for a thoracolumbar burst fracture

Because burst fractures often involve damage to the column and posterior structures of the spine, the fracture block may invade the spinal canal and compress the spinal cord or the cauda equina, causing corresponding neurological dysfunction. When a thoracolumbar burst fracture is accompanied by the presence of bone in the spinal canal, whether posterior surgery requires spinal canal incision decompression is still controversial. Computed tomography images of the thoracolumbar spine of a 31-year-old male with an L1 burst fracture and Mimics 10.0 were used to establish a three-dimensional fracture model for simulating the indirect reduction process. The model was imported into Ansys 10.0 (ANSYS, Inc., Canonsburg, PA), and a 1 to 10 mm displacement was loaded 10° behind the Z-axis on the upper endplate of the L1 vertebral body to simulate position reduction and open reduction. The displacement and stress changes in the intervertebral disc, fractured vertebral body and posterior longitudinal ligament were observed during reduction. Under a displacement loaded 10° behind the Z-axis, the maximum stress in the vertebral body was concentrated on the upper disc of the injured vertebrae. The maximum displacement was in the anterior edge of the vertebral body of the injured vertebrae, and the vertebral body height and the anterior lobes were essentially restored. When the displacement load was applied in the positive Z-axis direction, the maximum displacement was in the posterior longitudinal ligament behind the injured vertebrae. Under a 6 mm load, the posterior longitudinal ligament displacement was 11.3 mm. Under an 8 mm load, this displacement significantly increased to 15.0 mm, and the vertebral stress was not concentrated on the intervertebral disc. A reduction in the thoracolumbar burst fractures by positioning and distraction allowed the injured vertebrae to be restored to normal height and kyphosis. The reduction in the posterior longitudinal ligament can push the bone block in the spinal canal into the reset space and achieve a good reset.