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Risk of pedicle and spinous process violation during cortical bone trajectory screw placement in the lumbar spine

Risk of pedicle and spinous process violation during cortical bone trajectory screw placement in... Background: Previous studies have confirmed the feasibility of the cortical bone trajectory (CBT) technique. However, there are few reports on spinous process violation and screw penetration during the screw insertion. The purpose of this study was to evaluate the incidence of spinous process violation and screw penetration through the pedicle during CBT screw insertion. Methods: Computed tomography (CT) scans with normal lumbar structures were consecutively obtained and three-dimensional (3D) reconstructions of the lumbar spine were created. Bilateral CBT screw placement was simulated on each segment using a screw diameter of 4.5 mm, 5.0 mm, or 5.5 mm. Incidences of these complications were recorded and analyzed. Results: A total of 90 patients were enrolled. Spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% from L1 to L5, respectively, using 4.5 mm screws. A significant difference was found among the five segments but this was unconnected to gender or screw diameter. The incidence of screw penetration through the inner wall decreased from L1 to L4; in turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) and L4 (1.1–6.7%). This trend was reversed in L5 (6.7–16.7%). Moreover, screw penetration through the outer wall was rare. The incidence of screw penetration varied with screw size as well as lumbar level, but not with gender. Conclusions: There are more difficulties of CBT screw fixation in upper lumbar spine. The low rate of screw penetration, using 4.5 mm screws, suggests the safety for CBT fixation in the lumbar spine. Larger screws (5.0 mm or 5.5 mm) are more recommended for use in the lower lumbar spine. Moreover, CBT fixation in L5 deserves greater attention because of the unique morphology of the pedicle. Keywords: Cortical bone trajectory. Spinous process violation. Screw penetration. Three-dimensional simulation Background significant soft tissue dissection. Moreover, it should be The pedicle screw fixation technique is widely used as an noted that screw loosening or dislocation is a common effective surgical method for spinal segmental fixation. problem in traditional trajectory surgery in elderly patients Traditional pedicle screw fixation has been considered to with severe osteoporosis [1–3]. To overcome these defi- be the optimal method for it has high level of stability. ciencies, Santoni et al. [4] suggested the cortical bone tra- However, this technique is invasive and requires jectory (CBT) screw fixation technique as an alternative strategy for rigid fixation in the lumbar spine. CBT screws follow a specific trajectory from the pedicle to the cortical * Correspondence: jinliya122001@163.com bone surface, and improvement in screw purchase and re- Department of Orthopaedic Surgery, The Second Affiliated Hospital and duction of the loosening rate has been confirmed [5, 6]. Yuying Children’s Hospital of Wenzhou Medical University, 109 Xueyuanxi Road, Wenzhou 325000, Zhejiang, China © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 2 of 7 To date, this technique has been applied clinically as an al- placement was simulated on each segment. The screw ternative fixation method in osteoporosis patients, and has size and insertion method were bilaterally identical. The demonstrated satisfying clinical outcomes [7, 8]. More- simulation was performed by a spine surgeon. over, it is considered to be an effective salvage fixation technique for failed traditional fixation or adjacent verte- Screw trajectories bral disease [9]. Compared to traditional pedicle screw fix- CBT screw placement follows a medial-to-lateral path in ation, the CBT technique is also less invasive, involving the axial plane and a caudal-to-cephalad path in the sa- less soft tissue dissection, less blood loss, shorter operative gittal plane through the pedicle, engaging maximally time and shorter length of hospital stay [7]. with the cortical bone from the pedicle to the vertebral However, the CBT technique has some limitations. In body [4]. In this study, the target entry points and trajec- real surgeries, the posterior structures (mainly the spin- tories were based on the anteroposterior and lateral ous processes) are often considered to be a significant views of the 3D model. In the anteroposterior view, the obstruction to screw placement in this trajectory, espe- pedicle can be regarded as a clock face, which can assist cially in the upper lumbar spine. Thus, partial resection with intra-operative localization. The insertion was of the spinous processes and supraspinous ligament is started at the 7 o’clock position and aimed for a 1 often required, which may cause damage to the posterior o’clock orientation in the right pedicle, whereas insertion ligamentous complex participating in spinal stability. In in the left pedicle began at the 5 o’clock position and addition, due to the special trajectory of the CBT screw, aimed for an 11 o’clock orientation in the anteroposter- there remains a risk of screw penetration through the ior view (Fig. 2a) [10, 11]. To create parity, the endpoint pedicle in patients with small pedicles, which can result was set at the midpoint of the superior endplate without in nerve injuries and unstable fixation. None of these sit- perforation in the lateral view (Fig. 2b). This trajectory uations should be overlooked during the operation. was used for CBT screw placement in all lumbar levels. Presently, although morphometric and biochemical studies have confirmed the feasibility of the CBT tech- nique, there remains a lack of related reports on spinous Screw dimensions process violation and screw penetration during the screw Currently, the 4.5 mm screw is commonly used in clinical insertion process. Therefore, the purpose of this study surgery for CBT screw fixation. However, larger screws was to evaluate the risk of the above complications in are also recommended for stronger fixation strength [12]. CBT screw fixation and provide a reference for the clin- To provide a comparison among the various screw diame- ical application of this technique using three- ters, screws with a diameter of 4.5 mm, 5.0 mm, or 5.5 dimensional (3D) screw insertion simulation software. mm were used in the placement process in this study. Methods Inclusion and exclusion criteria All lumbar spinal CT scans (containing L1–5) for either trauma evaluation or for preoperative surgical planning at our institution were retrospectively reviewed between January 2017 and June 2018. Patients with a lumbar frac- ture, compression of the vertebral body, ankylosing spon- dylitis, deformity, lumbar tumor or infection, or history of spinal surgery, were excluded. Patients with age of < 40 were excluded. All CT scans were performed on a 16-slice CT scanner (Philips Brilliance 16; Philips Medical Systems, Eindho- ven, the Netherlands). Scan parameters included 120 kV, 200 mA, a 512 × 512 matrix, a layer thickness of 1 mm, and a pitch of 1 mm. Computer simulation CT images of the lumbar spine were manipulated using Mimics software (ver. 18.0; Materialise, Leuven, Belgium) and underwent 3D reconstruction. After the Fig. 1 The anteroposterior (a) and lateral (b) view of the three- removal of unnecessary anatomic structures, normal 3D dimensional lumbar model lumbar models were obtained (Fig. 1). Then, CBT screw Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 3 of 7 Fig. 2 The entry points and trajectories were shown. In the anteroposterior view (a), the pedicle can be regarded as a clock face; the insertion was started at the 5 o’clock (green circle) position and aimed for 11 o’clock (red circle) orientation in the left pedicle, whereas insertion in the right pedicle began at the 7 o’clock (green circle) position and aimed for 1 o’clock (red circle) orientation. The endpoint (red circle) was set at the midpoint of the superior endplate without perforation in the lateral view (b) Assessment of spinous process violation and screw Results penetration According to the selection criteria, 90 patients (48 males Following the predetermined entry points and trajector- and 42 females, mean age: 63.7 years, range: 40–85 years) ies, CBT screw placement finished in L1–5 (Fig. 3). After were enrolled in this study. All CT scans underwent 3D screw placement, spinous process violation or screw reconstruction and showed successful screw placement. penetration through the pedicle (through the inner and Given the lack of any statistical difference between the outer walls) could be directly observed in the 3D two sides, one screw insertion was regarded as a separate models (Fig. 4). Then, the incidence of the above study object. Thus, 900 screw insertions were contained complications was recorded and evaluated at each in this simulation (180 screws in each segment). level. Each level was compared with all other levels. Table 1 summarizes the incidence of spinous process The incidence of each complication among different violation and screw penetration through the pedicle (in- screwdiameters,aswellasby gender, wasalsocom- cluding the inner and outer walls) during the placement pared. The assessment was performed by an inde- process. The difference among screw sizes, as well as pendent spine surgeon. lumbar levels, is shown in Table 2. The incidence of spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% of segments from L1 to L5, respect- Statistical analyses ively, using 4.5 mm screws. L1 and L2 were clearly asso- SPSS software (ver. 22.0; SPSS, Inc., Chicago, IL, USA) ciated with a particularly high rate of spinous process was used for all statistical analyses. The chi-squared test violation, whereas such violation barely occurred in L4 or Fisher’s exact test was utilized to compare the incidence and L5. Similarly, 5.0 and 5.5 mm screws also showed a of the above complications by gender, among the three similar rate, and downward trend, of spinous process screw diameters, and among the five levels. A p-value < violation from L1 to L5. A significant difference was 0.05 was considered to indicate statistical significance. found among the five segments (p < 0.001); however, this Fig. 3 The illustration of successful CBT screw placement as shown on the coronal (a), sagittal (b) and axial (c) view Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 4 of 7 Fig. 4 The illustration of complications in CBT screws placement. a and b show spinous process violation in axial and coronal views. c Screw penetration through the inner wall of the pedicle. d Screw penetration through the outer wall of the pedicle Table 1 The incidence of spinous process violation and pedicle wall penetration Complication L1 (mm) L2 (mm) L3 (mm) L4 (mm) L5 (mm) 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 A (%) Male 62.5 64.6 65.6 52.1 52.1 53.1 25.0 26.0 26.0 0 0 0 0 0 0 Female 75.0 77.3 77.3 54.8 56.0 56.0 26.1 27.4 28.6 3.6 3.6 3.6 0 0 0 Total 68.3 70.5 71.1 53.3 53.8 54.4 25.5 26.7 27.2 1.7 1.7 1.7 0 0 0 p Value 0.072 0.060 0.083 0.719 0.603 0.704 0.855 0.839 0.704 0.100 0.100 0.100 ––– B (%) Male 13.5 19.8 29.1 8.3 22.9 32.9 1.0 8.3 20.8 0 1.0 3.1 3.1 7.3 12.5 Female 20.2 32.1 42.8 17.8 29.7 36.9 4.8 17.8 27.4 2.4 6.0 10.7 10.7 16.6 21.4 Total 16.7 25.5 35.5 12.7 26.1 34.4 2.8 12.7 23.8 1.1 3.3 6.7 6.7 11.7 16.7 p Value 0.229 0.058 0.056 0.056 0.297 0.516 0.186 0.056 0.304 0.216 0.099 0.069 0.069 0.051 0.066 C (%) Male 2.1 4.2 14.5 0 1.0 9.4 0 0 0 0 0 0 0 0 0 Female 6.0 10.0 14.2 2.4 3.6 6.0 0 0 4.8 0 0 0 0 0 0 Total 3.9 6.7 14.4 1.1 2.2 7.8 0 0 2.2 0 0 0 0 0 0 p Value 0.254 0.231 0.955 0.216 0.340 0.392 –– 0.186 ––– ––– A Spinous process violation, B Screw penetration through the inner wall of pedicle, C Screw penetration through the outer wall of pedicle, L Lumbar Comparison between genders Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 5 of 7 Table 2 The effect of lumbar level and screw size on three complications Complication Size (mm) L1 L2 L3 L4 L5 p value A (%) 4.5 68.3 53.3 25.5 1.7 0 < 0.001 5.0 70.5 53.8 26.7 1.7 0 < 0.001 5.5 71.1 54.4 27.2 1.7 0 < 0.001 p value 0.831 0.971 0.936 1.000 – B (%) 4.5 16.7 12.7 2.8 1.1 6.7 < 0.001 5.0 25.5 26.1 12.7 3.3 11.7 < 0.001 5.5 35.5 34.4 23.8 6.7 16.7 < 0.001 p value < 0.001 < 0.001 < 0.001 0.019 0.013 C (%) 4.5 3.9 1.1 0 0 0 < 0.001 5.0 6.7 2.2 0 0 0 < 0.001 5.5 14.4 7.8 2.8 0 0 < 0.001 p value 0.001 0.002 0.018 –– A Spinous process violation, B Screw penetration through the inner wall of pedicle, C Screw penetration through the outer wall of pedicle, L Lumbar Comparison among lumbar levels Comparisons among screw sizes appeared to be unconnected to gender (p > 0.05) or trajectories. Spinous process violation and screw pene- screw diameter (p > 0.05). tration through the pedicle are two of the most common In general, the incidence of screw penetration through complications and cannot be ignored operatively. the pedicle was not high and differed between the inner Given the lack of sufficient clinical data regarding and outer walls. The incidence of screw penetration these two complications, computer simulation software through the inner wall with varying screw sizes (4.5, 5.0, can be of great assistance in evaluating their incidence. or 5.5 mm) showed a downward trend from L1 to L4; in Such software enables trajectories to be adjusted without turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) breaking the specimen, and can test a large number of and L4 (1.1–6.7%). However, the incidence in L5 (6.7– patients in visible models. Through 3D reconstruction of 16.7%) reversed this downward trend. As shown in Table the lumbar spine and simulation of CBT screw place- 2, different levels showed a significantly different inci- ment, evaluation of the incidence of the two complica- dence of screw penetration through the inner wall (p < tions in each segment can be undertaken. Additionally, 0.001). Moreover, different screw sizes also resulted in simulated placements are conducive to determining the an apparent difference in the incidence on L1-L5 (p < entry point, insertion angle, and appropriate screw di- 0.05). In addition, screw penetration through the outer mensions prior to a real operation, and help reduce the wall was rare compared to that through the inner wall, incidence of intraoperative complications. and did not tend to occur in the lower lumbar spine. In real CBT surgery, the unique trajectory of pedicle The incidence of screw penetration through the outer screw fixation often causes spinous process violation, wall also varied with screw size and lumbar level. Not- where the posterior ligamentous complex can be a sig- ably, there was no significant difference in screw pene- nificant barrier to screw placement. To solve this prob- tration by gender. lem, partial resection of the spinous process and supraspinous ligament is usually required before screw Discussion insertion, especially in upper lumbar surgery. Cheng The CBT screw fixation technique, as a modified fix- et al. confirmed this in a cadaveric study [13]. They ation method for traditional pedicle screw fixation, has deemed the entry point to be close to the spinous attracted increasing attention and has already been ap- process, which may lead to compression between the plied in clinical surgery [7, 8]. To achieve stronger in- screw and the spinous process, as well as the lamina, ternal fixation, the CBT screw follows a unique without resecting the posterior element; this can ultim- trajectory from the pedicle to the cortical bone surface, ately result in the fracture of adjacent structures or tra- maximizing thread contact with the higher-density bone jectory deviations. In our study, the incidence of spinous surface [4]. CBT screw fixation is minimally invasive and process violation sequentially decreased from L1 to L5, shows superiority in patients with severe osteoporosis. which was in line with the gradual increase of lumbar However, some potential complications cannot be com- vertebrae width from L1 to L5. In L1 and L2 in particu- pletely avoided during the insertion process at particular lar, the high rate of spinous process violation, of about Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 6 of 7 50–70%, indicated that partial resection of the posterior incidence of screw penetration in L5 fixation should be structure would be inevitable in most upper lumbar sur- seriously considered. geries. In contrast, the low rate in the lower lumbar It is generally accepted that screw purchase is posi- spine suggested superior maneuverability in the corre- tively related to screw diameter and length [12, 19]. A sponding segments with this trajectory. consensus has been reached that CBT demands finer Screw penetration through the pedicle is among the and shorter screws than traditional techniques due to its common complications of pedicle screw fixation and special trajectory. However, it is usually considered that carries the risk of neurovascular injury and pedicle frac- CBT could make up for the decrease of screw purchase ture [14]. Through a systematic study of the anatomy of caused by smaller screws. Currently, the 4.5 mm screw is the lumbar pedicle, Li et al. [15] noted that the height of recommended for use in clinical surgery for CBT fix- the pedicle is greater than its width, and that the upper ation, to reduce the risk of screw penetration. In our and lower walls are formed of thicker cortical bone. study, the 5.0- and 5.5 mm screws also showed a relatively Thus, screw penetration through the pedicle mainly oc- low incidence of screw penetration, especially in the lower curs in the inner and outer walls rather than in the lumbar spine. However, space for a safety margin around upper and lower walls. Compared to the traditional tra- the screw in real surgery is required. The use of larger jectory, the unique trajectory in this technique may in- screws would reduce this space and increase the risk of crease the incidence of screw penetration during the pedicle fracture in real surgery. By investigating these con- placement process. Therefore, finer screws are usually cerns during the simulated operation, we determined that applied in real CBT surgeries to reduce the incidence of the space in the lower lumbar spine is adequate for place- screw penetration. Unlike the low incidence of screw ment of larger screws due to the larger size of the pedicle. penetration reported previously, screw penetration Additionally, the incidence of screw penetration was not through the pedicle (including the inner and outer walls) significantly related to screw size in the lower lumbar clearly occurred in some cases in our study. The inci- spine. Therefore, despite the higher incidence of screw dence of screw penetration was considered to be closely penetration with larger screws, the use of larger screws related to the morphology of the pedicle. As is already (5.0 mm or 5.5 mm) is feasible in lower lumbar CBT fix- known, the morphology of the pedicle, including the ation surgery to obtain stronger screw purchase. Nonethe- shape and pedicle axis angle, differs by lumbar level [11, less, surgeons should pay greater attention to fixation in 16, 17]. With the increase in pedicle size from the upper L5 with larger screws because of the high rate of screw to the lower lumbar spine, the incidence of screw pene- penetration. The preoperative measurement and evalu- tration obviously decreased, suggesting the relative safety ation of screw sizes can, to an extent, help reduce the risk of this trajectory in the lower lumbar spine. Neverthe- of screw penetration [11, 20]. less, the risk of nerve injury and fixation instability This study had some limitations. First, it was based on should not be ignored, especially in the upper lumbar a computer simulation which is not as realistic as a ca- spine. Additionally, screw penetration through the outer daveric study. Second, there was no consideration of the wall is uncommon following use of the medial-to-lateral size of the screw head and insertion tools, which inevit- trajectory, and is much safer than penetration through ably led to an underestimation of the rate of spinous the inner wall. Thus, screw penetration through the process violation. Third, the subjectivity of the operator inner wall is more noteworthy. may have a bias on the results. We were able to adjust Notably, the incidence of screw penetration through the entry points and insertion angles several times before the L5 pedicle inner wall was higher than in L4, which determining the correct trajectory for each case; this is was not consistent with the changes in lumbar pedicle not possible during an actual operation. Fourth, the rela- size. The reasons for this may be as follows. First, the tively small sample size could be problematic in terms of distinctive morphology of the L5 pedicle plays an essen- statistical analysis. Finally, race, age, height, and weight tial role. The greater pedicle axial angle and deeper lat- were not considered in this study because of the restric- eral recess compared to other levels increase the tions of sample. In spite of these deficiencies, our study likelihood of screw penetration in L5 fixation [18]. Like- indicated the feasibility and safety of CBT screw fixation, wise, traditional trajectory pedicle screw fixation also has especially in the lower lumbar spine. a certain rate of screw penetration through the inner wall despite the larger size of the L5 pedicle. However, Conclusions contrary to the traditional trajectory, CBT does not fol- In conclusion, due to the high incidence of spinous low the central axis of the pedicle and instead has a process violation, there are more difficulties of CBT fix- crossing angle with the pedicle. The greater the angle ation in upper lumbar spine and risk of posterior elem- between the screw and the pedicle results in the higher ent damage is higher. In addition, the low rate of screw the risk of screw penetration. Therefore, the high penetration through the pedicle, with a screw diameter Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 7 of 7 of 4.5 mm, suggests the safety of this method when car- posterior lumbar fusion: a systematic review and meta-analysis. Eur Spine J. 2019;28(7):1678–89. ried out with small screws. Larger screws (5 mm or 5.5 8. Lee GW, Son JH, Ahn MW, Kim HJ, Yeom JS. The comparison of pedicle mm) are more suitable for use in the lower lumbar spine screw and cortical screw in posterior lumbar interbody fusion: a prospective under certain conditions, to provide stronger screw pur- randomized noninferiority trial. Spine J. 2015;15(7):1519–26. 9. Rodriguez A, Neal M, Liu A, Somasundaram A, Hsu W, Branch CL. Novel chase. Moreover, CBT fixation in L5 deserves greater at- placement of cortical bone trajectory screws in previously instrumented tention due to the unique morphology of the pedicle pedicles for adjacent-segment lumbar disease using CT image-guided and its trajectory. In short, preoperative measurement navigation. Neurosurg Focus. 2014;36(3):E9. 10. Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K. In vivo and evaluation are of great importance in the choice of analysis of insertional torque during pedicle screwing using cortical bone surgical trajectory or screw size before a real operation. trajectory technique. Spine (Phila Pa 1976). 2014;39(4):E240–5. 11. Matsukawa K, Yato Y, Nemoto O, Imabayashi H, Asazuma T, Nemoto K. Abbreviations Morphometric measurement of cortical bone trajectory for lumbar pedicle CBT: Cortical bone trajectory; CT: Computed tomography; 3D: Three- screw insertion using computed tomography. J Spinal Disord Tec. 2013; dimensional 26(6):E248–53. 12. Matsukawa K, Yato Y, Imabayashi H, Hosogane N, Abe Y, Asazuma T, et al. Acknowledgements Biomechanical evaluation of fixation strength among different sizes of Not applicable. pedicle screws using the cortical bone trajectory: what is the ideal screw size for optimal fixation? Acta Neurochir. 2016;158(3):465–71. Authors’ contributions 13. Cheng WK, Akpolat YT, Inceoglu S, Patel S, Danisa OA. Pars and pedicle LJ contributed to the conception and design. NT collect and analyzed the fracture and screw loosening associated with cortical bone trajectory: a case data. LZ and JY drafted the manuscript. WN critically reviewed the series and proposed mechanism through a cadaveric study. Spine J. 2016; manuscript. All authors have read and approved the final manuscript. 16(2):e59–65. 14. Morales-Avalos R, Re Elizondo-Omana RE, Vilchez-Cavazos F, Martínez-Ponce Funding de León AR, Elizondo-Riojas G, Delgado-Brito M, et al. Vertebral fixation with This work was supported by the clinical research foundation of The Second a transpedicular approach. Relevance of anatomical and imaging studies. Affiliated Hospital of Wenzhou Medical University (SAHoWMU-CR2017–08- Acta Ortop Mex. 2012;26(6):402–11. 106). 15. Li B, Jiang B, Fu Z, Zhang D, Wang T. Accurate determination of isthmus of lumbar pedicle: a morphometric study using reformatted computed Availability of data and materials tomographic images. Spine (Phila Pa 1976). 2004;29(21):2438–44. All data generated or analyzed during this study are available upon 16. Chaynes P, Sol J, Vaysse P, Becue J, Lagarrigue J. Vertebral pedicle anatomy reasonable request from the corresponding author. in relation to pedicle screw fixation: a cadaver study. Surg Radiol Anat. 2001; 23(2):85–90. Ethics approval and consent to participate 17. Robertson P, Stewart N. The radiologic anatomy of the lumbar and This study was approved by the Ethics Committee at The Second Affiliated lumbosacral pedicles. Spine (Phila Pa 1976). 2000;25(6):709–15. Hospital of Wenzhou Medical University (#2017–56; Mar, 2017). 18. Sugisaki K, An H, Espinoza Orías A, Rhim R, Andersson GB, Inoue N. In vivo three-dimensional morphometric analysis of the lumbar pedicle isthmus. Consent for publication Spine (Phila Pa 1976). 2009;34(24):2599–604. Not applicable, as no identifying personal information is included in this 19. Misenhimer G, Peek R, Wiltse L, Rothman SL, Widell JE. Anatomic analysis of manuscript. pedicle cortical and cancellous diameter as related to screw size. Spine (Phila Pa 1976). 1989;14(4):367–72. Competing interests 20. Senoglu M, Karadag A, Kinali B, Bozkurt B, Middlebrooks EK, Grande AW. The authors declare that they have no competing interests. Cortical bone trajectory screw for lumbar fixation: a quantitative anatomical and morphometric evaluation. World Neurosurg. 2017;103:694–701. Received: 9 March 2020 Accepted: 23 July 2020 Publisher’sNote References Springer Nature remains neutral with regard to jurisdictional claims in 1. Cook SD, Salkeld SL, Stanley T, Faciane A, Miller SD. Biomechanical study of published maps and institutional affiliations. pedicle screw fixation in severely osteoporotic bone. Spine J. 2004;4(4):402– 2. Xuan J, Zhang D, Jin HM, Chen JX, Xu DL, Xu H, et al. Minimally invasive cortical bone trajectory screws placement via pedicle or pedicle rib unit in the lower thoracic spine: a cadaveric and radiographic study. Eur Spine J. 2016;25(12):4199–207. 3. Marengo N, Berjano P, Cofano F, Ajello M, Zenga F, Pilloni G, et al. Cortical bone trajectory screws for circumferential arthrodesis in lumbar degenerative spine: clinical and radiological outcomes of 101 cases. Eur Spine J. 2018;27(2):213–21. 4. Santoni BG, Hynes RA, McGilvray KC, Rodriguez-Canessa G, Lyons AS, Henson MA, et al. Cortical bone trajectory for lumbar pedicle screws. Spine J. 2009;9(5):366–73. 5. Matsukawa K, Yato Y, Imabayashi H, Hosogane N, Asazuma T, Nemoto K. Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study. J Neurosurg Spine. 2015;23(4):471–8. 6. Wray S, Mimran R, Vadapalli S, Shetye SS, McGilvray KC, Puttlitz CM. Pedicle screw placement in the lumbar spine: effect of trajectory and screw design on acute biomechanical purchase. J Neurosurg Spine. 2015;22(5):503–10. 7. Wang J, He X, Sun T. Comparative clinical efficacy and safety of cortical bone trajectory screw fixation and traditional pedicle screw fixation in http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png BMC Musculoskeletal Disorders Springer Journals

Risk of pedicle and spinous process violation during cortical bone trajectory screw placement in the lumbar spine

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10.1186/s12891-020-03535-4
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Abstract

Background: Previous studies have confirmed the feasibility of the cortical bone trajectory (CBT) technique. However, there are few reports on spinous process violation and screw penetration during the screw insertion. The purpose of this study was to evaluate the incidence of spinous process violation and screw penetration through the pedicle during CBT screw insertion. Methods: Computed tomography (CT) scans with normal lumbar structures were consecutively obtained and three-dimensional (3D) reconstructions of the lumbar spine were created. Bilateral CBT screw placement was simulated on each segment using a screw diameter of 4.5 mm, 5.0 mm, or 5.5 mm. Incidences of these complications were recorded and analyzed. Results: A total of 90 patients were enrolled. Spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% from L1 to L5, respectively, using 4.5 mm screws. A significant difference was found among the five segments but this was unconnected to gender or screw diameter. The incidence of screw penetration through the inner wall decreased from L1 to L4; in turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) and L4 (1.1–6.7%). This trend was reversed in L5 (6.7–16.7%). Moreover, screw penetration through the outer wall was rare. The incidence of screw penetration varied with screw size as well as lumbar level, but not with gender. Conclusions: There are more difficulties of CBT screw fixation in upper lumbar spine. The low rate of screw penetration, using 4.5 mm screws, suggests the safety for CBT fixation in the lumbar spine. Larger screws (5.0 mm or 5.5 mm) are more recommended for use in the lower lumbar spine. Moreover, CBT fixation in L5 deserves greater attention because of the unique morphology of the pedicle. Keywords: Cortical bone trajectory. Spinous process violation. Screw penetration. Three-dimensional simulation Background significant soft tissue dissection. Moreover, it should be The pedicle screw fixation technique is widely used as an noted that screw loosening or dislocation is a common effective surgical method for spinal segmental fixation. problem in traditional trajectory surgery in elderly patients Traditional pedicle screw fixation has been considered to with severe osteoporosis [1–3]. To overcome these defi- be the optimal method for it has high level of stability. ciencies, Santoni et al. [4] suggested the cortical bone tra- However, this technique is invasive and requires jectory (CBT) screw fixation technique as an alternative strategy for rigid fixation in the lumbar spine. CBT screws follow a specific trajectory from the pedicle to the cortical * Correspondence: jinliya122001@163.com bone surface, and improvement in screw purchase and re- Department of Orthopaedic Surgery, The Second Affiliated Hospital and duction of the loosening rate has been confirmed [5, 6]. Yuying Children’s Hospital of Wenzhou Medical University, 109 Xueyuanxi Road, Wenzhou 325000, Zhejiang, China © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 2 of 7 To date, this technique has been applied clinically as an al- placement was simulated on each segment. The screw ternative fixation method in osteoporosis patients, and has size and insertion method were bilaterally identical. The demonstrated satisfying clinical outcomes [7, 8]. More- simulation was performed by a spine surgeon. over, it is considered to be an effective salvage fixation technique for failed traditional fixation or adjacent verte- Screw trajectories bral disease [9]. Compared to traditional pedicle screw fix- CBT screw placement follows a medial-to-lateral path in ation, the CBT technique is also less invasive, involving the axial plane and a caudal-to-cephalad path in the sa- less soft tissue dissection, less blood loss, shorter operative gittal plane through the pedicle, engaging maximally time and shorter length of hospital stay [7]. with the cortical bone from the pedicle to the vertebral However, the CBT technique has some limitations. In body [4]. In this study, the target entry points and trajec- real surgeries, the posterior structures (mainly the spin- tories were based on the anteroposterior and lateral ous processes) are often considered to be a significant views of the 3D model. In the anteroposterior view, the obstruction to screw placement in this trajectory, espe- pedicle can be regarded as a clock face, which can assist cially in the upper lumbar spine. Thus, partial resection with intra-operative localization. The insertion was of the spinous processes and supraspinous ligament is started at the 7 o’clock position and aimed for a 1 often required, which may cause damage to the posterior o’clock orientation in the right pedicle, whereas insertion ligamentous complex participating in spinal stability. In in the left pedicle began at the 5 o’clock position and addition, due to the special trajectory of the CBT screw, aimed for an 11 o’clock orientation in the anteroposter- there remains a risk of screw penetration through the ior view (Fig. 2a) [10, 11]. To create parity, the endpoint pedicle in patients with small pedicles, which can result was set at the midpoint of the superior endplate without in nerve injuries and unstable fixation. None of these sit- perforation in the lateral view (Fig. 2b). This trajectory uations should be overlooked during the operation. was used for CBT screw placement in all lumbar levels. Presently, although morphometric and biochemical studies have confirmed the feasibility of the CBT tech- nique, there remains a lack of related reports on spinous Screw dimensions process violation and screw penetration during the screw Currently, the 4.5 mm screw is commonly used in clinical insertion process. Therefore, the purpose of this study surgery for CBT screw fixation. However, larger screws was to evaluate the risk of the above complications in are also recommended for stronger fixation strength [12]. CBT screw fixation and provide a reference for the clin- To provide a comparison among the various screw diame- ical application of this technique using three- ters, screws with a diameter of 4.5 mm, 5.0 mm, or 5.5 dimensional (3D) screw insertion simulation software. mm were used in the placement process in this study. Methods Inclusion and exclusion criteria All lumbar spinal CT scans (containing L1–5) for either trauma evaluation or for preoperative surgical planning at our institution were retrospectively reviewed between January 2017 and June 2018. Patients with a lumbar frac- ture, compression of the vertebral body, ankylosing spon- dylitis, deformity, lumbar tumor or infection, or history of spinal surgery, were excluded. Patients with age of < 40 were excluded. All CT scans were performed on a 16-slice CT scanner (Philips Brilliance 16; Philips Medical Systems, Eindho- ven, the Netherlands). Scan parameters included 120 kV, 200 mA, a 512 × 512 matrix, a layer thickness of 1 mm, and a pitch of 1 mm. Computer simulation CT images of the lumbar spine were manipulated using Mimics software (ver. 18.0; Materialise, Leuven, Belgium) and underwent 3D reconstruction. After the Fig. 1 The anteroposterior (a) and lateral (b) view of the three- removal of unnecessary anatomic structures, normal 3D dimensional lumbar model lumbar models were obtained (Fig. 1). Then, CBT screw Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 3 of 7 Fig. 2 The entry points and trajectories were shown. In the anteroposterior view (a), the pedicle can be regarded as a clock face; the insertion was started at the 5 o’clock (green circle) position and aimed for 11 o’clock (red circle) orientation in the left pedicle, whereas insertion in the right pedicle began at the 7 o’clock (green circle) position and aimed for 1 o’clock (red circle) orientation. The endpoint (red circle) was set at the midpoint of the superior endplate without perforation in the lateral view (b) Assessment of spinous process violation and screw Results penetration According to the selection criteria, 90 patients (48 males Following the predetermined entry points and trajector- and 42 females, mean age: 63.7 years, range: 40–85 years) ies, CBT screw placement finished in L1–5 (Fig. 3). After were enrolled in this study. All CT scans underwent 3D screw placement, spinous process violation or screw reconstruction and showed successful screw placement. penetration through the pedicle (through the inner and Given the lack of any statistical difference between the outer walls) could be directly observed in the 3D two sides, one screw insertion was regarded as a separate models (Fig. 4). Then, the incidence of the above study object. Thus, 900 screw insertions were contained complications was recorded and evaluated at each in this simulation (180 screws in each segment). level. Each level was compared with all other levels. Table 1 summarizes the incidence of spinous process The incidence of each complication among different violation and screw penetration through the pedicle (in- screwdiameters,aswellasby gender, wasalsocom- cluding the inner and outer walls) during the placement pared. The assessment was performed by an inde- process. The difference among screw sizes, as well as pendent spine surgeon. lumbar levels, is shown in Table 2. The incidence of spinous process violation was observed in 68.3, 53.3, 25.5, 1.7, and 0% of segments from L1 to L5, respect- Statistical analyses ively, using 4.5 mm screws. L1 and L2 were clearly asso- SPSS software (ver. 22.0; SPSS, Inc., Chicago, IL, USA) ciated with a particularly high rate of spinous process was used for all statistical analyses. The chi-squared test violation, whereas such violation barely occurred in L4 or Fisher’s exact test was utilized to compare the incidence and L5. Similarly, 5.0 and 5.5 mm screws also showed a of the above complications by gender, among the three similar rate, and downward trend, of spinous process screw diameters, and among the five levels. A p-value < violation from L1 to L5. A significant difference was 0.05 was considered to indicate statistical significance. found among the five segments (p < 0.001); however, this Fig. 3 The illustration of successful CBT screw placement as shown on the coronal (a), sagittal (b) and axial (c) view Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 4 of 7 Fig. 4 The illustration of complications in CBT screws placement. a and b show spinous process violation in axial and coronal views. c Screw penetration through the inner wall of the pedicle. d Screw penetration through the outer wall of the pedicle Table 1 The incidence of spinous process violation and pedicle wall penetration Complication L1 (mm) L2 (mm) L3 (mm) L4 (mm) L5 (mm) 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 4.5 5.0 5.5 A (%) Male 62.5 64.6 65.6 52.1 52.1 53.1 25.0 26.0 26.0 0 0 0 0 0 0 Female 75.0 77.3 77.3 54.8 56.0 56.0 26.1 27.4 28.6 3.6 3.6 3.6 0 0 0 Total 68.3 70.5 71.1 53.3 53.8 54.4 25.5 26.7 27.2 1.7 1.7 1.7 0 0 0 p Value 0.072 0.060 0.083 0.719 0.603 0.704 0.855 0.839 0.704 0.100 0.100 0.100 ––– B (%) Male 13.5 19.8 29.1 8.3 22.9 32.9 1.0 8.3 20.8 0 1.0 3.1 3.1 7.3 12.5 Female 20.2 32.1 42.8 17.8 29.7 36.9 4.8 17.8 27.4 2.4 6.0 10.7 10.7 16.6 21.4 Total 16.7 25.5 35.5 12.7 26.1 34.4 2.8 12.7 23.8 1.1 3.3 6.7 6.7 11.7 16.7 p Value 0.229 0.058 0.056 0.056 0.297 0.516 0.186 0.056 0.304 0.216 0.099 0.069 0.069 0.051 0.066 C (%) Male 2.1 4.2 14.5 0 1.0 9.4 0 0 0 0 0 0 0 0 0 Female 6.0 10.0 14.2 2.4 3.6 6.0 0 0 4.8 0 0 0 0 0 0 Total 3.9 6.7 14.4 1.1 2.2 7.8 0 0 2.2 0 0 0 0 0 0 p Value 0.254 0.231 0.955 0.216 0.340 0.392 –– 0.186 ––– ––– A Spinous process violation, B Screw penetration through the inner wall of pedicle, C Screw penetration through the outer wall of pedicle, L Lumbar Comparison between genders Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 5 of 7 Table 2 The effect of lumbar level and screw size on three complications Complication Size (mm) L1 L2 L3 L4 L5 p value A (%) 4.5 68.3 53.3 25.5 1.7 0 < 0.001 5.0 70.5 53.8 26.7 1.7 0 < 0.001 5.5 71.1 54.4 27.2 1.7 0 < 0.001 p value 0.831 0.971 0.936 1.000 – B (%) 4.5 16.7 12.7 2.8 1.1 6.7 < 0.001 5.0 25.5 26.1 12.7 3.3 11.7 < 0.001 5.5 35.5 34.4 23.8 6.7 16.7 < 0.001 p value < 0.001 < 0.001 < 0.001 0.019 0.013 C (%) 4.5 3.9 1.1 0 0 0 < 0.001 5.0 6.7 2.2 0 0 0 < 0.001 5.5 14.4 7.8 2.8 0 0 < 0.001 p value 0.001 0.002 0.018 –– A Spinous process violation, B Screw penetration through the inner wall of pedicle, C Screw penetration through the outer wall of pedicle, L Lumbar Comparison among lumbar levels Comparisons among screw sizes appeared to be unconnected to gender (p > 0.05) or trajectories. Spinous process violation and screw pene- screw diameter (p > 0.05). tration through the pedicle are two of the most common In general, the incidence of screw penetration through complications and cannot be ignored operatively. the pedicle was not high and differed between the inner Given the lack of sufficient clinical data regarding and outer walls. The incidence of screw penetration these two complications, computer simulation software through the inner wall with varying screw sizes (4.5, 5.0, can be of great assistance in evaluating their incidence. or 5.5 mm) showed a downward trend from L1 to L4; in Such software enables trajectories to be adjusted without turn, L1 (16.7–35.5%), L2 (12.7–34.4%), L3 (2.8–23.8%) breaking the specimen, and can test a large number of and L4 (1.1–6.7%). However, the incidence in L5 (6.7– patients in visible models. Through 3D reconstruction of 16.7%) reversed this downward trend. As shown in Table the lumbar spine and simulation of CBT screw place- 2, different levels showed a significantly different inci- ment, evaluation of the incidence of the two complica- dence of screw penetration through the inner wall (p < tions in each segment can be undertaken. Additionally, 0.001). Moreover, different screw sizes also resulted in simulated placements are conducive to determining the an apparent difference in the incidence on L1-L5 (p < entry point, insertion angle, and appropriate screw di- 0.05). In addition, screw penetration through the outer mensions prior to a real operation, and help reduce the wall was rare compared to that through the inner wall, incidence of intraoperative complications. and did not tend to occur in the lower lumbar spine. In real CBT surgery, the unique trajectory of pedicle The incidence of screw penetration through the outer screw fixation often causes spinous process violation, wall also varied with screw size and lumbar level. Not- where the posterior ligamentous complex can be a sig- ably, there was no significant difference in screw pene- nificant barrier to screw placement. To solve this prob- tration by gender. lem, partial resection of the spinous process and supraspinous ligament is usually required before screw Discussion insertion, especially in upper lumbar surgery. Cheng The CBT screw fixation technique, as a modified fix- et al. confirmed this in a cadaveric study [13]. They ation method for traditional pedicle screw fixation, has deemed the entry point to be close to the spinous attracted increasing attention and has already been ap- process, which may lead to compression between the plied in clinical surgery [7, 8]. To achieve stronger in- screw and the spinous process, as well as the lamina, ternal fixation, the CBT screw follows a unique without resecting the posterior element; this can ultim- trajectory from the pedicle to the cortical bone surface, ately result in the fracture of adjacent structures or tra- maximizing thread contact with the higher-density bone jectory deviations. In our study, the incidence of spinous surface [4]. CBT screw fixation is minimally invasive and process violation sequentially decreased from L1 to L5, shows superiority in patients with severe osteoporosis. which was in line with the gradual increase of lumbar However, some potential complications cannot be com- vertebrae width from L1 to L5. In L1 and L2 in particu- pletely avoided during the insertion process at particular lar, the high rate of spinous process violation, of about Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 6 of 7 50–70%, indicated that partial resection of the posterior incidence of screw penetration in L5 fixation should be structure would be inevitable in most upper lumbar sur- seriously considered. geries. In contrast, the low rate in the lower lumbar It is generally accepted that screw purchase is posi- spine suggested superior maneuverability in the corre- tively related to screw diameter and length [12, 19]. A sponding segments with this trajectory. consensus has been reached that CBT demands finer Screw penetration through the pedicle is among the and shorter screws than traditional techniques due to its common complications of pedicle screw fixation and special trajectory. However, it is usually considered that carries the risk of neurovascular injury and pedicle frac- CBT could make up for the decrease of screw purchase ture [14]. Through a systematic study of the anatomy of caused by smaller screws. Currently, the 4.5 mm screw is the lumbar pedicle, Li et al. [15] noted that the height of recommended for use in clinical surgery for CBT fix- the pedicle is greater than its width, and that the upper ation, to reduce the risk of screw penetration. In our and lower walls are formed of thicker cortical bone. study, the 5.0- and 5.5 mm screws also showed a relatively Thus, screw penetration through the pedicle mainly oc- low incidence of screw penetration, especially in the lower curs in the inner and outer walls rather than in the lumbar spine. However, space for a safety margin around upper and lower walls. Compared to the traditional tra- the screw in real surgery is required. The use of larger jectory, the unique trajectory in this technique may in- screws would reduce this space and increase the risk of crease the incidence of screw penetration during the pedicle fracture in real surgery. By investigating these con- placement process. Therefore, finer screws are usually cerns during the simulated operation, we determined that applied in real CBT surgeries to reduce the incidence of the space in the lower lumbar spine is adequate for place- screw penetration. Unlike the low incidence of screw ment of larger screws due to the larger size of the pedicle. penetration reported previously, screw penetration Additionally, the incidence of screw penetration was not through the pedicle (including the inner and outer walls) significantly related to screw size in the lower lumbar clearly occurred in some cases in our study. The inci- spine. Therefore, despite the higher incidence of screw dence of screw penetration was considered to be closely penetration with larger screws, the use of larger screws related to the morphology of the pedicle. As is already (5.0 mm or 5.5 mm) is feasible in lower lumbar CBT fix- known, the morphology of the pedicle, including the ation surgery to obtain stronger screw purchase. Nonethe- shape and pedicle axis angle, differs by lumbar level [11, less, surgeons should pay greater attention to fixation in 16, 17]. With the increase in pedicle size from the upper L5 with larger screws because of the high rate of screw to the lower lumbar spine, the incidence of screw pene- penetration. The preoperative measurement and evalu- tration obviously decreased, suggesting the relative safety ation of screw sizes can, to an extent, help reduce the risk of this trajectory in the lower lumbar spine. Neverthe- of screw penetration [11, 20]. less, the risk of nerve injury and fixation instability This study had some limitations. First, it was based on should not be ignored, especially in the upper lumbar a computer simulation which is not as realistic as a ca- spine. Additionally, screw penetration through the outer daveric study. Second, there was no consideration of the wall is uncommon following use of the medial-to-lateral size of the screw head and insertion tools, which inevit- trajectory, and is much safer than penetration through ably led to an underestimation of the rate of spinous the inner wall. Thus, screw penetration through the process violation. Third, the subjectivity of the operator inner wall is more noteworthy. may have a bias on the results. We were able to adjust Notably, the incidence of screw penetration through the entry points and insertion angles several times before the L5 pedicle inner wall was higher than in L4, which determining the correct trajectory for each case; this is was not consistent with the changes in lumbar pedicle not possible during an actual operation. Fourth, the rela- size. The reasons for this may be as follows. First, the tively small sample size could be problematic in terms of distinctive morphology of the L5 pedicle plays an essen- statistical analysis. Finally, race, age, height, and weight tial role. The greater pedicle axial angle and deeper lat- were not considered in this study because of the restric- eral recess compared to other levels increase the tions of sample. In spite of these deficiencies, our study likelihood of screw penetration in L5 fixation [18]. Like- indicated the feasibility and safety of CBT screw fixation, wise, traditional trajectory pedicle screw fixation also has especially in the lower lumbar spine. a certain rate of screw penetration through the inner wall despite the larger size of the L5 pedicle. However, Conclusions contrary to the traditional trajectory, CBT does not fol- In conclusion, due to the high incidence of spinous low the central axis of the pedicle and instead has a process violation, there are more difficulties of CBT fix- crossing angle with the pedicle. The greater the angle ation in upper lumbar spine and risk of posterior elem- between the screw and the pedicle results in the higher ent damage is higher. In addition, the low rate of screw the risk of screw penetration. Therefore, the high penetration through the pedicle, with a screw diameter Zhang et al. BMC Musculoskeletal Disorders (2020) 21:536 Page 7 of 7 of 4.5 mm, suggests the safety of this method when car- posterior lumbar fusion: a systematic review and meta-analysis. Eur Spine J. 2019;28(7):1678–89. ried out with small screws. Larger screws (5 mm or 5.5 8. Lee GW, Son JH, Ahn MW, Kim HJ, Yeom JS. The comparison of pedicle mm) are more suitable for use in the lower lumbar spine screw and cortical screw in posterior lumbar interbody fusion: a prospective under certain conditions, to provide stronger screw pur- randomized noninferiority trial. Spine J. 2015;15(7):1519–26. 9. Rodriguez A, Neal M, Liu A, Somasundaram A, Hsu W, Branch CL. Novel chase. Moreover, CBT fixation in L5 deserves greater at- placement of cortical bone trajectory screws in previously instrumented tention due to the unique morphology of the pedicle pedicles for adjacent-segment lumbar disease using CT image-guided and its trajectory. In short, preoperative measurement navigation. Neurosurg Focus. 2014;36(3):E9. 10. Matsukawa K, Yato Y, Kato T, Imabayashi H, Asazuma T, Nemoto K. In vivo and evaluation are of great importance in the choice of analysis of insertional torque during pedicle screwing using cortical bone surgical trajectory or screw size before a real operation. trajectory technique. Spine (Phila Pa 1976). 2014;39(4):E240–5. 11. Matsukawa K, Yato Y, Nemoto O, Imabayashi H, Asazuma T, Nemoto K. Abbreviations Morphometric measurement of cortical bone trajectory for lumbar pedicle CBT: Cortical bone trajectory; CT: Computed tomography; 3D: Three- screw insertion using computed tomography. J Spinal Disord Tec. 2013; dimensional 26(6):E248–53. 12. Matsukawa K, Yato Y, Imabayashi H, Hosogane N, Abe Y, Asazuma T, et al. Acknowledgements Biomechanical evaluation of fixation strength among different sizes of Not applicable. pedicle screws using the cortical bone trajectory: what is the ideal screw size for optimal fixation? Acta Neurochir. 2016;158(3):465–71. Authors’ contributions 13. Cheng WK, Akpolat YT, Inceoglu S, Patel S, Danisa OA. Pars and pedicle LJ contributed to the conception and design. NT collect and analyzed the fracture and screw loosening associated with cortical bone trajectory: a case data. LZ and JY drafted the manuscript. WN critically reviewed the series and proposed mechanism through a cadaveric study. Spine J. 2016; manuscript. All authors have read and approved the final manuscript. 16(2):e59–65. 14. Morales-Avalos R, Re Elizondo-Omana RE, Vilchez-Cavazos F, Martínez-Ponce Funding de León AR, Elizondo-Riojas G, Delgado-Brito M, et al. Vertebral fixation with This work was supported by the clinical research foundation of The Second a transpedicular approach. Relevance of anatomical and imaging studies. Affiliated Hospital of Wenzhou Medical University (SAHoWMU-CR2017–08- Acta Ortop Mex. 2012;26(6):402–11. 106). 15. Li B, Jiang B, Fu Z, Zhang D, Wang T. Accurate determination of isthmus of lumbar pedicle: a morphometric study using reformatted computed Availability of data and materials tomographic images. Spine (Phila Pa 1976). 2004;29(21):2438–44. All data generated or analyzed during this study are available upon 16. Chaynes P, Sol J, Vaysse P, Becue J, Lagarrigue J. Vertebral pedicle anatomy reasonable request from the corresponding author. in relation to pedicle screw fixation: a cadaver study. Surg Radiol Anat. 2001; 23(2):85–90. Ethics approval and consent to participate 17. Robertson P, Stewart N. The radiologic anatomy of the lumbar and This study was approved by the Ethics Committee at The Second Affiliated lumbosacral pedicles. Spine (Phila Pa 1976). 2000;25(6):709–15. Hospital of Wenzhou Medical University (#2017–56; Mar, 2017). 18. Sugisaki K, An H, Espinoza Orías A, Rhim R, Andersson GB, Inoue N. In vivo three-dimensional morphometric analysis of the lumbar pedicle isthmus. Consent for publication Spine (Phila Pa 1976). 2009;34(24):2599–604. Not applicable, as no identifying personal information is included in this 19. Misenhimer G, Peek R, Wiltse L, Rothman SL, Widell JE. Anatomic analysis of manuscript. pedicle cortical and cancellous diameter as related to screw size. Spine (Phila Pa 1976). 1989;14(4):367–72. Competing interests 20. Senoglu M, Karadag A, Kinali B, Bozkurt B, Middlebrooks EK, Grande AW. The authors declare that they have no competing interests. Cortical bone trajectory screw for lumbar fixation: a quantitative anatomical and morphometric evaluation. 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