Pedicle screw adjustments affect stability of thoracolumbar burst fracture

Study Design. An in vitro biomechanical study of the stabilizing effect of pedicle screw instrumentation on experimental thoracolumbar burst fractures . Objectives. To evaluate the effects of different adjustments applied by the pedicle screw fixation device on the stability of the spine-device constru ct. Summary of Background Data. Pedicle screw devices are widely used to accomp lish spinal reduction and provide stability to an injured spine. In previou s biomechanical studies the stability of the spine-device constructs has be en examined for many devices. However, no study has quantitatively assessed the associations between the device adjustments and the stability of the c onstruct. Methods. Five-vertebrae human cadaveric specimens with burst fracture at Ll vertebra were studied. Pedicle screw fixation device was attached to the T 12 and L2 vertebrae. Five device adjustments (pure compression, pure distra ction, pure extension, a combination distraction-extension, and neutral pos ture) were studied. Multidirectional flexibility test was performed when in tact, after burst fracture, and after each device adjustment to document sp inal stability. Results. The construct stability had a complex association to the device ad justment. For example, the maximum flexion and extension stabilities were a chieved by pure compression and distraction-extension combination adjustmen ts, respectively. Pure distraction and pure extension adjustments decreased the construct stability. Conclusions. The device adjustments affected the spinal construct stability differently in different directions. Although pure compression provided th e most stability in most directions, the combined distraction-extension adj ustment may be more suitable considering the neural decompression also.