Incomplete insertion of pedicle screws in a standard construct reduces the fatigue life: A biomechanical analysis

Autoři: Yo-Lun Chu aff001;  Chia-Hsien Chen aff002;  Fon-Yih Tsuang aff005;  Chang-Jung Chiang aff002;  Yueh Wu aff001;  Yi-Jie Kuo aff001
Působiště autorů: Department of Orthopedic Surgery, Wan Fang Hospital, Taipei Medical University, Taipei, Taiwan aff001;  Department of Orthopedics, Shuang Ho Hospital, Taipei Medical University, New Taipei City, Taiwan aff002;  Department of Orthopedic Surgery, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan aff003;  Graduate Institute of Biomedical Materials and Tissue Engineering, College of Biomedical Engineering, Taipei Medical University, Taipei, Taiwan aff004;  Division of Neurosurgery, Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan aff005
Vyšlo v časopise: PLoS ONE 14(11)
Kategorie: Research Article
doi: 10.1371/journal.pone.0224699


Pedicle screws are commonly used for posterior stabilization of the spine. When used in deformed or degenerated segments, the pedicle screws are often not fully inserted into the bone, but instead the threaded portion is exposed by 1 or 2 threads to accommodate rod placement and ensure alignment between the tulip of the screw and the rod. However, broken pedicle screws have been reported with the use of this method. The aim of this study was to determine how the fatigue life of the screw is affected by not fully inserting the screw into the bone. Spinal constructs were evaluated in accordance with ASTM F1717. The following three screw positions were subjected to compression bending fatigue loading; (i) pedicle screw fully inserted in the test block with no threads exposed (EXP-T0), (ii) pedicle screw inserted with one thread exposed outside the test block (EXP-T1), (iii) pedicle screw inserted with two threads exposed outside the test block (EXP-T2). Corresponding finite element models FEM-T0, FEM-T1 and FEM-T2 were also constructed and subjected to the same axial loading as the experimental groups to analyze the stress distribution in the pedicle screws and rods. The results showed that under a 190 N axial load, the EXP-T0 group survived the full 5 million cycles, the EXP-T1 group failed at 3.7 million cycles on average and the EXP-T2 groups failed at 1.0 million cycles on average, while the fatigue strength of both the EXP-T1 and EXP-T2 groups was 170 N. The constructs failed through fracture of the pedicle screw. In comparison to the FEM-T0 model, the maximum von Mises stress on the pedicle screw in the FEM-T1 and FEM-T2 models increased by 39% and 58%, respectively. In conclusion, this study demonstrated a drastic decrease in the fatigue life of pedicle screws when they are not full inserted into the plastic block.

Klíčová slova:

Bone fracture – Finite element analysis – Material fatigue – Medical implants – Spine – Stiffness – Spinal fusion – Metal fatigue


1. Goel VK, Winterbottom JM, Weinstein JN. A method for the fatigue testing of pedicle screw fixation devices. J Biomech [Internet]. 1994 Nov [cited 2019 Mar 28];27(11):1383–8. Available from: doi: 10.1016/0021-9290(94)90048-5 7798289

2. Cobian D, Heiderscheit B, Daehn N, Anderson PA, Spenciner D, Graham J, et al. Comparison of Daily Motion of the Cervical and Lumbar Spine to ASTM F2423-11 and ISO 18192–1.2011 Standard Testing. J ASTM Int [Internet]. 2012 Nov 3 [cited 2019 Mar 28];9(1):103522. Available from:

3. Brasiliense LBC, Lazaro BCR, Reyes PM, Newcomb AGUS, Turner JL, Crandall DG, et al. Characteristics of immediate and fatigue strength of a dual-threaded pedicle screw in cadaveric spines. Spine J. 2013 Aug;13(8):947–56. doi: 10.1016/j.spinee.2013.03.010 23602373

4. Fatihhi SJ, Harun MN, Abdul Kadir MR, Abdullah J, Kamarul T, Öchsner A, et al. Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study. Ann Biomed Eng. 2015 Oct 22;43(10):2487–502. doi: 10.1007/s10439-015-1305-8 25828397

5. Shinohara K, Takigawa T, Tanaka M, Sugimoto Y, Arataki S, Yamane K, et al. Implant failure of titanium versus cobalt-chromium growing rods in early-onset scoliosis. Spine (Phila Pa 1976). 2016 Mar 4;41(6):502–7.

6. Smith JS, Shaffrey E, Klineberg E, Shaffrey CI, Lafage V, Schwab FJ, et al. Prospective multicenter assessment of risk factors for rod fracture following surgery for adult spinal deformity. J Neurosurg Spine. 2014 Dec 1;21(6):994–1003. doi: 10.3171/2014.9.SPINE131176 25325175

7. 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. Med Eng Phys [Internet]. 2005 Jul [cited 2019 Mar 28];27(6):487–96. Available from: doi: 10.1016/j.medengphy.2004.12.007 15990065

8. Zdeblick JBHG. Is Infuse Bone Graft Superior to Autograft Bone? An Integrated Analysis of Clinical Trials Using the Lt-cage Lumbar Tapered Fusion Device. J Spinal Disord &amp. 2003;16(2):113–22.

9. La Barbera L, Galbusera F, Villa T, Costa F, Wilke H-J. ASTM F1717 standard for the preclinical evaluation of posterior spinal fixators: Can we improve it? Proc Inst Mech Eng Part H J Eng Med [Internet]. 2014 Oct 15 [cited 2019 Mar 16];228(10):1014–26. Available from:

10. Giacaglia GEO, Lamas W de Q. Pedicle screw rupture: A case study. Case Stud Eng Fail Anal [Internet]. 2015 Oct 1 [cited 2019 Apr 10];4:64–75. Available from:

11. Stambough JL, El Khatib F, Genaidy AM, Huston RL. Strength and fatigue resistance of thoracolumbar spine implants: an experimental study of selected clinical devices. J Spinal Disord [Internet]. 1999 Oct [cited 2019 Mar 28];12(5):410–4. Available from: 10549706

12. Chen P-Q, Lin S-J, Wu S-S, So H. Mechanical Performance of the New Posterior Spinal Implant: Effect of Materials, Connecting Plate, and Pedicle Screw Design. Spine (Phila Pa 1976) [Internet]. 2003 May 1 [cited 2019 Mar 28];28(9):881–6. Available from:

13. Stanford RE, Loefler AH, Stanford PM, Walsh WR. Multiaxial pedicle screw designs: static and dynamic mechanical testing. Spine (Phila Pa 1976) [Internet]. 2004 Feb 15 [cited 2019 Mar 28];29(4):367–75. Available from:

14. La Barbera L, Galbusera F, Wilke HJ, Villa T. Preclinical evaluation of posterior spine stabilization devices: can we compare in vitro and in vivo loads on the instrumentation? Eur Spine J. 2017 Jan 1;26(1):200–9. doi: 10.1007/s00586-016-4766-z 27637903

15. La Barbera L, Ottardi C, Villa T. Comparative analysis of international standards for the fatigue testing of posterior spinal fixation systems: The importance of preload in ISO 12189. Spine J. 2015 Oct 1;15(10):2290–6.

16. Villa T, La Barbera L, Galbusera F. Comparative analysis of international standards for the fatigue testing of posterior spinal fixation systems. Spine J. 2014 Apr 1;14(4):695–704. doi: 10.1016/j.spinee.2013.08.032 24268390

17. La Barbera L, Villa T. Toward the definition of a new worst-case paradigm for the preclinical evaluation of posterior spine stabilization devices. Proc Inst Mech Eng Part H J Eng Med. 2017 Feb 1;231(2):176–85.

18. ASTM F2706-18. Standard Test Methods for Occipital-Cervical and Occipital-Cervical-Thoracic Spinal Implant Constructs in a Vertebrectomy Model. ASTM International, West Conshohocken, PA. 2018.

19. ASTM F1717-18. Standard test methods for spinal implant constructs in a vertebrectomy model. ASTM Int West Conshohocken, PA [Internet]. 2018 [cited 2019 Mar 11];1–16. Available from:

20. Galbusera F, Schmidt H, Wilke H-J. Lumbar interbody fusion: a parametric investigation of a novel cage design with and without posterior instrumentation. Eur Spine J [Internet]. 2012 Mar [cited 2019 Mar 11];21(3):455–62. Available from: doi: 10.1007/s00586-011-2014-0 21918923

21. Schmidt H, Heuer F, Wilke H-J. Which axial and bending stiffnesses of posterior implants are required to design a flexible lumbar stabilization system? J Biomech [Internet]. 2009 Jan 5 [cited 2019 Mar 11];42(1):48–54. Available from: doi: 10.1016/j.jbiomech.2008.10.005 19038390

22. Rohlmann A, Graichen F, Bergmann G. Loads on an internal spinal fixation device during physical therapy. Phys Ther [Internet]. 2002 Jan [cited 2019 Mar 28];82(1):44–52. Available from: doi: 10.1093/ptj/82.1.44 11784277

23. Dickman CA, Fessler RG, MacMillan M, Haid RW. Transpedicular screw-rod fixation of the lumbar spine: Operative technique and outcome in 104 cases. J Neurosurg. 1992;77(6):860–70. doi: 10.3171/jns.1992.77.6.0860 1432127

24. Niu CC, Chen WJ, Chen LH, Shih CH. Reduction-fixation spinal system in spondylolisthesis. undefined. 1996;

25. Wang H, Zhao Y, Mo Z, Han J, Chen Y, Yu H, et al. Comparison of short-segment monoaxial and polyaxial pedicle screw fixation combined with intermediate screws in traumatic thoracolumbar fractures: a finite element study and clinical radiographic review. Clinics [Internet]. 2017 Oct [cited 2019 Apr 10];72(10):609. Available from: doi: 10.6061/clinics/2017(10)04 29160423

26. Yang T, Chen K, Lv Y. Fatigue Life Analysis of Fixed Structure of Posterior Thoracolumbar Pedicle Screw. Engineering [Internet]. 2013 Oct 16 [cited 2019 Mar 28];05(10):292–6. Available from:

27. La Barbera L, Galbusera F, Wilke H-J, Villa T. Preclinical evaluation of posterior spine stabilization devices: can the current standards represent basic everyday life activities? Eur Spine J [Internet]. 2016 Sep 28 [cited 2019 Apr 10];25(9):2909–18. Available from: doi: 10.1007/s00586-016-4622-1 27236658

28. La Barbera L, Costa F, Villa T. ISO 12189 standard for the preclinical evaluation of posterior spinal stabilization devices—II: A parametric comparative study. Proc Inst Mech Eng H [Internet]. 2016 Feb [cited 2019 Oct 14];230(2):134–44. Available from: doi: 10.1177/0954411915621588 26673809

Článek vyšel v časopise


2019 Číslo 11