Clinical Relevance of Accuracy of Pedicle Screw Placement

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Abstract
Study Design. The location of pedicle screws (n = 244) and the increase in the pedicle diameter were determined by computed tomography after screw removal in 50 patients with 360° lumbar fusions. The neurologic findings were examined before and after surgery. Objectives. To evaluate the correlation between the accuracy of pedicle screw placement and preoperative and postoperative neurologic findings. Summary of Background Data. Incorrect placement of pedicle screws that was detected by computed tomography has been published in several studies. Simultaneous pathologic neurologic deficits are thought to be created by an eccentric screw track. Methods. Two observers controlled the screw tracts and pedicle diameters. The results were compared with preoperative and postoperative neurologic findings. Results. Fifty-nine percent (144 of 244) of screws were placed centrally in the pedicle. More than half of the eccentric screws (100, 41%; medial 79, 32.4%; lateral 21, 8.6%) penetrated the pedicle wall less than 2 mm (51; 20.9%). In only one patient (0.5%) a radicular irritation was found without objective electrophysiologic correlation when the screw was more than 6 mm medial to the pedicle wall. After screw removal, an insignificant increase in the size of the pedicle diameter in L1-S1 was noted. Conclusions. Experienced surgeons implant pedicle screws with an accuracy of approximately 80%. The accuracy could be improved by using image-guided insertion equipment. The neurologic symptoms are rarely influenced by an eccentric pedicle screw tract even if penetration of the pedicle wall is more than 6 mm. The results stress the importance of preoperative planning (pedicle diameter, pedicle angle, screw length) when implanting transpedicular fixators.