Biomechanics of sacropelvic fixation: a comprehensive finite element comparison of three techniques

  • Fabio GalbuseraEmail author
  • Gloria Casaroli
  • Ruchi Chande
  • Derek Lindsey
  • Tomaso Villa
  • Scott Yerby
  • Ali Mesiwala
  • Matteo Panico
  • Enrico Gallazzi
  • Marco Brayda-Bruno
Original Article



Sacropelvic fixation is frequently used in combination with thoracolumbar instrumentation for complex deformity correction and is commonly associated with pseudoarthrosis, implant failure and loosening. This study compared pedicle screw fixation (PED) with three different sacropelvic fixation techniques, namely iliac screws (IL), S2 alar-iliac screws (S2AI) and laterally placed triangular titanium implants (SI), all in combination with lumbosacral instrumentation, accounting for implant micromotion.


Existing finite element models of pelvis-L5 of three patients including lumbopelvic instrumentation were utilized. Moments of 7.5 Nm in the three directions combined with a 500 N compressive load were simulated. Measured metrics included flexibility, instrumentation stresses and bone–implant interface loads.


Fixation effectively reduced the sacroiliac flexibility. Compared to PED, IL and S2AI induced a reduction in peak stresses in the S1 pedicle screws. Rod stresses were mostly unaffected by S2AI and SI, but IL demonstrated a stress increase. In comparison with a previous work depicting full osteointegration, SI was found to have similar instrumentation stresses as those due to PED.


Fixation with triangular implants did not result in stress increase on the lumbosacral instrumentation, likely due to the lack of connection with the posterior rods. IL and S2AI had a mild protective effect on S1 pedicle screws in terms of stresses and bone–implant loads. IL resulted in an increase in the rod stresses. A comparison between this study and previous work incorporating full osteointegration demonstrates how these results may be applied clinically to better understand the effects of different treatments on patient outcomes.

Graphic abstract

These slides can be retrieved under Electronic Supplementary Material.


Pelvic fixation Alar-iliac screws Iliac screws Screw loosening Micromotion Pseudoarthrosis 



Fabio Galbusera received research support from SI-BONE, Inc., to conduct this study.

Author contribution

GC, MP and FG developed the finite element models. FG developed the computer programs used for the pre-processing of the models. RC and DL supported and revised the development of the models. GC, RC, FG and DL prepared the draft of the manuscript. All authors critically evaluated and interpreted the results of the calculations, revised the manuscript and approved the submitted version. 


The study has been funded by SI-BONE, Inc.

Compliance with ethical standards

Conflict of interest

RC, DL and SY are employed at SI-BONE, Inc., and have stock/stock options in SI-BONE, Inc. AM is a consultant of SI-BONE, Inc. and conducted clinical research for SI-BONE, Inc.

Supplementary material

586_2019_6225_MOESM1_ESM.pptx (1.4 mb)
Supplementary file1 (PPTX 1402 kb)


  1. 1.
    Esmende SM, Shah KN, Daniels AH (2018) Spinopelvic fixation. J Am Acad Orthop Surg 26(11):396–401. CrossRefPubMedGoogle Scholar
  2. 2.
    Kim YJ, Bridwell KH, Lenke LG et al (2006) Pseudarthrosis in long adult spinal deformity instrumentation and fusion to the sacrum: prevalence and risk factor analysis of 144 cases. Spine 31(20):2329–2336CrossRefGoogle Scholar
  3. 3.
    Lee C, Chung SS, Choi SW et al (2010) Critical length of fusion requiring additional fixation to prevent nonunion of the lumbosacral junction. Spine 35(6):E206–E211CrossRefGoogle Scholar
  4. 4.
    Kebaish KM (2010) Sacropelvic fixation: techniques and complications. Spine 35(25):2245–2251CrossRefGoogle Scholar
  5. 5.
    Mazur MD, Ravindra VM, Schmidt MH et al (2015) Unplanned reoperation after lumbopelvic fixation with S-2 alar-iliac screws or iliac bolts. J Neurosurg Spine 23(1):67–76CrossRefGoogle Scholar
  6. 6.
    Guler UO, Cetin E, Yaman O et al (2015) Sacropelvic fixation in adult spinal deformity (ASD); a very high rate of mechanical failure. Eur Spine J 24(5):1085–1091CrossRefGoogle Scholar
  7. 7.
    Ilyas H, Place H, Puryear A (2015) A comparison of early clinical and radiographic complications of iliac screw fixation versus S2 alar iliac (S2AI) fixation in the adult and pediatric populations. J Spinal Disord Tech 28(4):E199–E205CrossRefGoogle Scholar
  8. 8.
    Ishida W, Elder BD, Holmes C et al (2017) Comparison between S2-alar-iliac screw fixation and iliac screw fixation in adult deformity surgery: reoperation rates and spinopelvic parameters. Global Spine J 7(7):672–680CrossRefGoogle Scholar
  9. 9.
    Elder BD, Ishida W, Lo SL et al (2017) Use of S2-alar-iliac screws associated with less complications than iliac screws in adult lumbosacropelvic fixation. Spine 42(3):E142–E149CrossRefGoogle Scholar
  10. 10.
    Sohn S, Park TH, Chung CK et al (2018) Biomechanical characterization of three iliac screw fixation techniques: a finite element study. J Clin Neurosci 52:109–114CrossRefGoogle Scholar
  11. 11.
    Burns CB, Dua K, Trasolini NA et al (2016) Biomechanical comparison of spinopelvic fixation constructs: iliac screw versus S2-alar-iliac screw. Spine Deform 4(1):10–15CrossRefGoogle Scholar
  12. 12.
    Cunningham BW, Sponseller PD, Murgatroyd AA et al (2019) A comprehensive biomechanical analysis of sacral alar iliac fixation: an in vitro human cadaveric model. J Neurosurg Spine 30(3):367–375CrossRefGoogle Scholar
  13. 13.
    Volkheimer D, Reichel H, Wilke H et al (2017) Is pelvic fixation the only option to provide additional stability to the sacral anchorage in long lumbar instrumentation? A comparative biomechanical study of new techniques. Clin Biomech 43:34–39CrossRefGoogle Scholar
  14. 14.
    Hoernschemeyer DG, Pashuck TD, Pfeiffer FM (2017) Analysis of the s2 alar-iliac screw as compared with the traditional iliac screw: does it increase stability with sacroiliac fixation of the spine? Spine J 17(6):875–879CrossRefGoogle Scholar
  15. 15.
    Hlubek RJ, Godzik J, Newcomb AGUS et al (2019) Iliac screws may not be necessary in long-segment constructs with L5–S1 anterior lumbar interbody fusion: cadaveric study of stability and instrumentation strain. Spine J. 19(5):942–950CrossRefGoogle Scholar
  16. 16.
    Lebwohl NH, Cunningham BW, Dmitriev A et al (2002) Biomechanical comparison of lumbosacral fixation techniques in a calf spine model. Spine 27(21):2312–2320CrossRefGoogle Scholar
  17. 17.
    Fleischer GD, Kim YJ, Ferrara LA et al (2012) Biomechanical analysis of sacral screw strain and range of motion in long posterior spinal fixation constructs: effects of lumbosacral fixation strategies in reducing sacral screw strains. Spine 37(3):E163–E169CrossRefGoogle Scholar
  18. 18.
    Kleck CJ, Illing D, Lindley EM et al (2017) Strain in posterior instrumentation resulted by different combinations of posterior and anterior devices for long spine fusion constructs. Spine Deform 5(1):27–36CrossRefGoogle Scholar
  19. 19.
    Galbusera F, Niemeyer F (2018) Mathematical and finite element modeling. Galbusera F. Elsevier, Amsterdam, pp 239–255Google Scholar
  20. 20.
    Casaroli G, Galbusera F, Chande R, Lindsey D, Mesiwala A, Yerby S, Brayda-Bruno M (2019) Evaluation of iliac screw, S2 alar-iliac screw and laterally placed triangular titanium implants for sacropelvic fixation in combination with posterior lumbar instrumentation: a finite element study. Eur Spine J 28(7):1724–1732CrossRefGoogle Scholar
  21. 21.
    MacLeod AR, Pankaj P, Simpson AHR (2012) Does screw–bone interface modelling matter in finite element analyses? J Biomech 45(9):1712–1716CrossRefGoogle Scholar
  22. 22.
    Wieding J, Souffrant R, Fritsche A et al (2012) Finite element analysis of osteosynthesis screw fixation in the bone stock: an appropriate method for automatic screw modelling. PLoS ONE 7(3):e33776CrossRefGoogle Scholar
  23. 23.
    Noailly J, Lacroix D (2012) Finite element modelling of the spine. Biomaterials for spinal surgery. Elsevier, Amsterdam, pp 144–234eCrossRefGoogle Scholar
  24. 24.
    Noailly J, Malandrino A, Galbusera F (2014) Computational modelling of spinal implants. In: Computational modelling of biomechanics and biotribology in the musculoskeletal system. Elsevier, Amsterdam, pp 447–484Google Scholar
  25. 25.
    Luca A, Ottardi C, Sasso M et al (2017) Instrumentation failure following pedicle subtraction osteotomy: the role of rod material, diameter, and multi-rod constructs. Eur Spine J 26(3):764–770CrossRefGoogle Scholar
  26. 26.
    Lee S, Im Y, Kim K et al (2011) Comparison of cervical spine biomechanics after fixed-and mobile-core artificial disc replacement: a finite element analysis. Spine 36(9):700–708CrossRefGoogle Scholar
  27. 27.
    Galbusera F, Bellini CM, Anasetti F et al (2011) Rigid and flexible spinal stabilization devices: a biomechanical comparison. Med Eng Phys 33(4):490–496CrossRefGoogle Scholar
  28. 28.
    Rohlmann A, Burra NK, Zander T et al (2007) Comparison of the effects of bilateral posterior dynamic and rigid fixation devices on the loads in the lumbar spine: a finite element analysis. Eur Spine J 16(8):1223–1231CrossRefGoogle Scholar
  29. 29.
    Rohlmann A, Boustani HN, Bergmann G et al (2010) Effect of a pedicle-screw-based motion preservation system on lumbar spine biomechanics: a probabilistic finite element study with subsequent sensitivity analysis. J Biomech 43(15):2963–2969CrossRefGoogle Scholar
  30. 30.
    Tsuchiya K, Bridwell KH, Kuklo TR et al (2006) Minimum 5-year analysis of L5–S1 fusion using sacropelvic fixation (bilateral S1 and iliac screws) for spinal deformity. Spine 31(3):303–308CrossRefGoogle Scholar
  31. 31.
    V Sabourin JL Gillick JS Harrop 2019 Instrumentation-Related Complications. In: Complications in neurosurgery. Elsevier, Amsterdam. pp 320–324Google Scholar
  32. 32.
    Weistroffer JK, Perra JH, Lonstein JE et al (2008) Complications in long fusions to the sacrum for adult scoliosis: minimum five-year analysis of fifty patients. Spine 33(13):1478–1483CrossRefGoogle Scholar
  33. 33.
    Wilke HJ, Wenger K, Claes L (1998) Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants. Eur Spine J 7(2):148–154CrossRefGoogle Scholar
  34. 34.
    Lindsey DP, Parrish R, Gundanna M et al (2018) Biomechanics of unilateral and bilateral sacroiliac joint stabilization. J Neurosurg Spine 28(3):326–332CrossRefGoogle Scholar
  35. 35.
    Soriano-Baron H, Lindsey DP, Rodriguez-Martinez N et al (2015) The effect of implant placement on sacroiliac joint range of motion: posterior versus transarticular. Spine 40(9):E525–E530CrossRefGoogle Scholar
  36. 36.
    Sutterlin CE, Field A, Ferrara LA et al (2016) Range of motion, sacral screw and rod strain in long posterior spinal constructs: a biomechanical comparison between S2 alar iliac screws with traditional fixation strategies. J Spine Surg 2(4):266–276. CrossRefPubMedPubMedCentralGoogle Scholar
  37. 37.
    Viceconti M, Henney A, Morley-Fletcher E (2016) In silico clinical trials: how computer simulation will transform the biomedical industry. Int J Clin Trials 3(2):37–46CrossRefGoogle Scholar
  38. 38.
    Schmidt H, Galbusera F, Rohlmann A et al (2012) Effect of multilevel lumbar disc arthroplasty on spine kinematics and facet joint loads in flexion and extension: a finite element analysis. Eur Spine J 21(Suppl 5):S663–S674. CrossRefPubMedGoogle Scholar
  39. 39.
    Dreischarf M, Rohlmann A, Bergmann G et al (2011) Optimised loads for the simulation of axial rotation in the lumbar spine. J Biomech 44(12):2323–2327. CrossRefPubMedGoogle Scholar
  40. 40.
    Rohlmann A, Zander T, Rao M et al (2009) Applying a follower load delivers realistic results for simulating standing. J Biomech 42(10):1520–1526. CrossRefPubMedGoogle Scholar
  41. 41.
    Rohlmann A, Zander T, Rao M et al (2009) Realistic loading conditions for upper body bending. J Biomech 42(7):884–890. CrossRefPubMedGoogle Scholar
  42. 42.
    Chevalier Y, Matsuura M, Krüger S et al (2018) Micro-CT and micro-FE analysis of pedicle screw fixation under different loading conditions. J Biomech 70:204–211CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Fabio Galbusera
    • 1
    Email author
  • Gloria Casaroli
    • 1
  • Ruchi Chande
    • 2
  • Derek Lindsey
    • 2
  • Tomaso Villa
    • 3
  • Scott Yerby
    • 2
  • Ali Mesiwala
    • 4
  • Matteo Panico
    • 1
    • 3
  • Enrico Gallazzi
    • 1
  • Marco Brayda-Bruno
    • 1
  1. 1.Laboratory of Biological Structures MechanicsIRCCS Istituto Ortopedico GaleazziMilanItaly
  2. 2.SI-BONE, IncSan JoseUSA
  3. 3.Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”Politecnico Di MilanoMilanItaly
  4. 4.Southern California Center for Neuroscience and SpinePomonaUSA

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