Biomechanics of sacropelvic fixation: a comprehensive finite element comparison of three techniques
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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.
KeywordsPelvic fixation Alar-iliac screws Iliac screws Screw loosening Micromotion Pseudoarthrosis
Fabio Galbusera received research support from SI-BONE, Inc., to conduct this study.
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.
- 19.Galbusera F, Niemeyer F (2018) Mathematical and finite element modeling. Galbusera F. Elsevier, Amsterdam, pp 239–255Google Scholar
- 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
- 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
- 31.V Sabourin JL Gillick JS Harrop 2019 Instrumentation-Related Complications. In: Complications in neurosurgery. Elsevier, Amsterdam. pp 320–324Google Scholar
- 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. https://doi.org/10.21037/jss.2016.11.01 CrossRefPubMedPubMedCentralGoogle Scholar