Pullout strength of reinserted pedicle screws using the previous entry point and trajectory
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(2019) 14:205
RESEARCH ARTICLE
Open Access
Pullout strength of reinserted pedicle screws using the previous entry point and trajectory Xuanwu Huang1†, Zixiang Huang3†, Liwei Xu2,3, Dongzhu Liang4, Meichao Zhang4 and Hui Zhang2,3*
Abstract Purpose: This study compared the biomechanics of reinserted pedicle screws using the previous entry point and trajectory with those of correctly inserted pedicle screws. Methods: The study used 18 lumbar vertebrae (L1–6) from three fresh calf spines to insert 6.5 × 40-mm pedicle screws. A control screw was inserted correctly along the axis of one pedicle, while an experimental screw was reinserted completely using the previous entry point and trajectory in the other pedicle. The experimental screw was removed after being completely inserted in group A and after 80% of the total trajectory inserted in group B. And the experimental screw was removed after 60% of the total trajectory was reached in group C. The biomechanical values of the pedicle screws were measured. Results: There were no significant differences in pedicle screw axial pullout strength between reinserted screws and correct screws in the 3 groups (PA = 0.463, PB = 0.753, PC = 0.753). Stiffness measurement increased for the reinserted screw compared with that of the control screw. Fracturing was observed between the vertebral body and pedicle. Conclusion: Theoretically, a surgeon can remove the pedicle screw when necessary, inspect the trajectory, and reinsert the screw using the previous entry point and trajectory. Keywords: Pedicle screw, Reinserted screw, Pullout strength, Lumbar spine, In vitro study
Introduction Pedicle screw instrumentation is considered standard for treatment of spinal degenerative diseases, fractures, tumors, and deformities [1–3]. Although pedicle screw instrumentation is strong, malposition of a screw, resulting in a lateral wall breach and shorter screw insertion length in the pedicle, occurs frequently, especially with the freehand technique [4, 5]. The rate of pedicle screw malposition ranges from 5 to 41% [6, 7]. When pedicle screw malposition occurs during surgery, the screw is removed and reinserted along a correct entry point and trajectory. What is more, if a shorter pedicle screw is used because of insufficient * Correspondence: [email protected] † Xuanwu Huang and Zixiang Huang are co-first authors. 2 The Second School of Clinical Medicine, Southern Medical University, No. 253, Gongye Road, Haizhu District, Guangzhou 510282, China 3 Department of Spine Surgery, Guangdong Second Provincial General Hospital, No. 466, Xingang Road, Haizhu District, Guangzhou 510317, China Full list of author information is available at the end of the article
preoperative preparation, the surgeon may remove the pedicle screw and reinsert a longer pedicle screw. Many studies reported that the biomechanical strength of a redirected pedicle screw is less than that of a correctly placed screw [5, 8–11]. Brasiliense et al. [8] compared the pullout strength of 3 cortical perforation pedicle screws wit
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