The effects of pedicle screw adjustments on the anatomical reduction of thoracolumbar burst fractures

The short segmental pedicle screw device is widely used for the decompression of neural elements and reduction of normal anatomy. Many biomechanical studies concerning proper decompression are available. However, no study has determined the optimal device adjustment for reduction of the burst fracture to the normal anatomy. In this study, cadaveric thoracolumbar spine specimens (T11-L3) with L1 burst fractures were studied. A pedicle screw device was attached to the pedicles of the T12 and L2 vertebrae. Spinal postural changes were determined due to a set of eight clinically relevant adjustments of the device. The adjustments were combinations of axial translation (distraction/compression) and extension. The adjustments caused varying changes in spinal posture. The sequence of applying the translation and extension had no effect on the spinal posture changes. The adjustment combining 5 mm distraction with 6degrees extension brought the burst fracture closest to the intact state, compared to all other adjustments. With this adjustment, on average the spine became 0.9 mm. compressed and 2.0degrees lordotic, compared to the intact. The results of the study show that the device adjustments of axial translation and sagittal angulation can be applied in any sequence, with the same results. The combination of 5 mm distraction with 6degrees extension was the device adjustment that produced the closest anatomical reduction.