The effects of pedicle screw adjustments on neural spaces in burst fracture surgery

Study Design. An in vitro biomechanical study of experimental burst fractur es and a pedicle screw device. Objectives. To investigate the effects that adjustments of a pedicle screw device have on the neural spaces of the burst fracture. Summary of Background Data. Decompression of the neural spaces is important for the recovery of neural function after a burst fracture. No studies, ex perimental or clinical, are available that have attempted to relate the ped icle screw device adjustments to the decompression of the neural spaces. Methods. Burst fractures were produced at L1 vertebra in nine human lumbar spine specimens. Pedicle screw devices were attached to T12 and L2. Eight d evice adjustments, consisting of pure translations (distraction or compress ion), pure extension, and combinations of translation and extension were ap plied. The dimensional changes in the canal and the superior and inferior i ntervertebral foramens were measured. Functions of restoration and improvem ent were determined for the adjustments to evaluate the effects of each adj ustment and to determine the optimal adjustment. Analysis of variance was u sed to find statistically significant differences, with significance set at P values less than 0.05. Results. Significant differences were observed in the results of the eight adjustments. The most effective adjustments were the combination of 5-mm di straction with 6 degrees extension or 10-mm distraction alone. The worst ad justment was 5 mm of compression. Conclusions. Restoring compromised neural spaces in a patient with burst fr acture is necessary. The choice of a device adjustment was found to be an i mportant factor in the decompression of the neural spaces after the burst f racture. Combined distraction with extension and distraction alone were fou nd to decompress the canal and intervertebral foramens maximally in a burst fracture.