Biomechanical evaluation of the pedicle screw insertion depth and role of cross-link in thoracolumbar junction fracture surgery: a finite element study under compressive loads




finite element model, thoracolumbar junction, corpectomy, transpedicular bicortical screws fixation, cross-link


Introduction. The thoracolumbar junction is one of the most frequently damaged parts of the human spine when exposed to a traumatic factor. Corpectomy in combination with posterior decompression and restoration of the spinal support function is often performed using an interbody implant and posterior transpedicular stabilization to achieve adequate decompression and stabilization in severe traumatic injuries of this level.

The surgery of this type is characterized by significant instability of the operated segment and determines increased requirements for the rigidity and reliability of posterior fixation. We have modeled the situation of a two-level corpectomy with subsequent replacement of bodies with a mesh implant and posterior transpedicular stabilization with 8 screws.

Objective. To study the stress-strain state of the thoracolumbar spine model after resection of the Th12-L1 vertebrae with different variants of transpedicular fixation under the influence of a compressive load.

Materials and methods. A mathematical finite element model of the human thoracolumbar spine has been developed, the components of which are the Th9 ‒ Th11 and L2-L5 vertebrae (vertebrae Th12-L1 are removed), as well as elements of hardware - interbody support and transpedicular system. Four variants of transpedicular fixation were modeled: using short screws and long screws passing through the cortical layer of anterior wall of vertebral body, as well as two cross links and without them. The stress-strain state of the models was studied under the influence of a vertical compressive distributed load, which was applied to the body of the Th9 vertebra and its articular surfaces. The load value was 350 N, corresponding to the weight of the upper body.

Results. d It was found that transpedicular fixation of the thoracolumbar vertebrae with the use of long screws reduces the level of tension in the bone elements of the models. In the area of screw entry into the pedicle of the T10, T11, L2 and L3 vertebral arch, the load when using short screws was 3.1, 1.7, 3.9 and 12.1 MPa, respectively, when using bicortically installed screws - 2.9, 1.8, 3.8 and 10.6 MPa. The addition of two cross-links also reduces the maximum load values in critical areas of the model to a certain extent. In case of short screws combination and two cross-links, the load in these areas was 2.8, 1.7, 3.6 and 11.5 MPa, when using bicortical screws and cross-links - 2.8, 1.6, 3.3 and 9.3 MPa. The study of the stress-strain state of other parts of the model revealed a similar trend.

Conclusions. The use of long screws with fixation in the cortical bone of anterior part of the vertebral bodies reduces the level of tension in the bone elements of the models. The use of cross links provides greater rigidity to the transpedicular system, that also reduces the tension in the bone tissue.

Author Biographies

Oleksii S.  Nekhlopochyn, Romodanov Neurosurgery Institute, Kyiv

Spine Surgery Department

Vadim V. Verbov, Romodanov Neurosurgery Institute, Kyiv

Restorative Neurosurgery Department

Michael Yu. Karpinsky, Sytenko Institute of Spine and Joint Pathology, Kharkiv

Biomechanics Laboratory

Oleksandr V. Yaresko, Sytenko Institute of Spine and Joint Pathology, Kharkiv

Biomechanics Laboratory


1. den Ouden LP, Smits AJ, Stadhouder A, Feller R, Deunk J, Bloemers FW. Epidemiology of Spinal Fractures in a Level One Trauma Center in the Netherlands: A 10 Years Review. Spine (Phila Pa 1976). 2019;44(10):732-739. [CrossRef] [PubMed]

2. Krug EG, Sharma GK, Lozano R. The global burden of injuries. Am J Public Health. 2000 Apr;90(4):523-6. [CrossRef] [PubMed] [PubMed Central]

3. Greenfield RT, 3rd, Grant RE, Bryant D. Pedicle screw fixation in the management of unstable thoracolumbar spine injuries. Orthop Rev. 1992;21(6):701-706. [PubMed]

4. Wood KB, Li W, Lebl DR, Ploumis A. Management of thoracolumbar spine fractures. Spine J. 2014;14(1):145-164. [CrossRef] [PubMed]

5. Bolesta MJ, Caron T, Chinthakunta SR, Vazifeh PN, Khalil S. Pedicle screw instrumentation of thoracolumbar burst fractures: Biomechanical evaluation of screw configuration with pedicle screws at the level of the fracture. Int J Spine Surg. 2012 Dec 1;6:200-5. [CrossRef] [PubMed] [PubMed Central]

6. Lehman RA, Jr., Polly DW, Jr., Kuklo TR, Cunningham B, Kirk KL, Belmont PJ, Jr. Straight-forward versus anatomic trajectory technique of thoracic pedicle screw fixation: a biomechanical analysis. Spine (Phila Pa 1976). 2003;28(18):2058-2065. [CrossRef] [PubMed]

7. Krag MH, Beynnon BD, Pope MH, DeCoster TA. Depth of insertion of transpedicular vertebral screws into human vertebrae: effect upon screw-vertebra interface strength. J Spinal Disord. 1988;1(4):287-294. [CrossRef] [PubMed]

8. Cornaz F, Widmer J, Snedeker JG, Spirig JM, Farshad M. Cross-links in posterior pedicle screw-rod instrumentation of the spine: a systematic review on mechanical, biomechanical, numerical and clinical studies. Eur Spine J. 2021;30(1):34-49. [CrossRef] [PubMed]

9. Jindal R, Jasani V, Sandal D, Garg SK. Current status of short segment fixation in thoracolumbar spine injuries. J Clin Orthop Trauma. 2020 Sep-Oct;11(5):770-777. [CrossRef] [PubMed] [PubMed Central]

10. Nekhlopochin A, Nekhlopochin S, Karpinsky M, Shvets A, Karpinskaya E, Yaresko A. [Mathematical Analysis and Optimization of Design Characteristics of Stabilizing Vertebral Body Replacing Systems for Subaxial Cervical Fusion Using the Finite Element Method]. Hirurgiâ pozvonočnika. 2017;14(1):37-45. Russian. [CrossRef]

11. Cowin SC. Bone Mechanics Handbook. 2nd ed. Boca Raton: CRC Press; 2001.

12. Boccaccio A, Pappalettere C. Mechanobiology of Fracture Healing: Basic Principles and Applications in Orthodontics and Orthopaedics. In: Klika V, editor. Theoretical Biomechanics2011.

13. Niinomi M. Mechanical biocompatibilities of titanium alloys for biomedical applications. J Mech Behav Biomed Mater. 2008;1(1):30-42. [CrossRef] [PubMed]

14. Obraztsov IF, Adamovich IS, Barer IS. Problemy prochnosti v biomekhanike. Moscow: Vysshaya shkola; 1988. Russian.

15. Zenkevich OK. Metod konechnykh elementov v tekhnike. Moscow: Mir; 1975. Russian.

16. Alyamovskiy AA. SolidWorks/COSMOSWorks. Inzhenernyy analiz metodom konechnykh elementov. Moscow: DMK Press; 2004. Russian.

17. Mina A, Mohammed RAK. Biomechanical Evaluation of Segmental Pedicle Screw Fixation in Thoracolumbar Fracture: A Finite Element Study. Orthopedics and Rheumatology Open Access Journal. 2018;12(3). [CrossRef]

18. Chen C-S, Chen W-J, Cheng C-K, Jao S-HE, Chueh S-C, Wang C-C. Failure analysis of broken pedicle screws on spinal instrumentation. Medical Engineering & Physics. 2005;27(6):487-496. [CrossRef]

19. Disch AC, Luzzati A, Melcher I, Schaser KD, Feraboli F, Schmoelz W. Three-dimensional stiffness in a thoracolumbar en-bloc spondylectomy model: a biomechanical in vitro study. Clin Biomech (Bristol, Avon). 2007;22(9):957-964. [CrossRef] [PubMed]

20. Disch AC, Schaser KD, Melcher I, Luzzati A, Feraboli F, Schmoelz W. En bloc spondylectomy reconstructions in a biomechanical in-vitro study. Eur Spine J. 2008 May;17(5):715-25. [CrossRef] [PubMed] [PubMed Central]

21. Weinstein JN, Rydevik BL, Rauschning W. Anatomic and technical considerations of pedicle screw fixation. Clin Orthop Relat Res. 1992(284):34-46. [PubMed]

22. Shibasaki Y, Tsutsui S, Yamamoto E, Murakami K, Yoshida M, Yamada H. A bicortical pedicle screw in the caudad trajectory is the best option for the fixation of an osteoporotic vertebra: An in-vitro experimental study using synthetic lumbar osteoporotic bone models. Clin Biomech (Bristol, Avon). 2020;72:150-154. [CrossRef] [PubMed]

23. Matsuzaki H, Tokuhashi Y, Matsumoto F, Hoshino M, Kiuchi T, Toriyama S. Problems and solutions of pedicle screw plate fixation of lumbar spine. Spine (Phila Pa 1976). 1990;15(11):1159-1165. [CrossRef] [PubMed]

24. Galbusera F, Volkheimer D, Reitmaier S, Berger-Roscher N, Kienle A, Wilke HJ. Pedicle screw loosening: a clinically relevant complication? Eur Spine J. 2015;24(5):1005-1016. [CrossRef] [PubMed]

25. Lynn G, Mukherjee DP, Kruse RN, Sadasivan KK, Albright JA. Mechanical stability of thoracolumbar pedicle screw fixation. The effect of crosslinks. Spine (Phila Pa 1976). 1997;22(14):1568-1572; discussion 1573. [CrossRef] [PubMed]

26. Wahba GM, Bhatia N, Bui CN, Lee KH, Lee TQ. Biomechanical evaluation of short-segment posterior instrumentation with and without crosslinks in a human cadaveric unstable thoracolumbar burst fracture model. Spine (Phila Pa 1976). 2010;35(3):278-285. [CrossRef] [PubMed]



How to Cite

Nekhlopochyn, O. S., Verbov, V. V., Karpinsky, M. Y., & Yaresko, O. V. (2021). Biomechanical evaluation of the pedicle screw insertion depth and role of cross-link in thoracolumbar junction fracture surgery: a finite element study under compressive loads. Ukrainian Neurosurgical Journal, 27(3), 25–32.



Original articles