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Biomechanical analysis of rod contouring in posterior spinal instrumentation and fusion for 3D correction of adolescent idiopathic scoliosis

  • Biomechanics
  • Published:
Spine Deformity Aims and scope Submit manuscript

Abstract

Purpose

To biomechanically evaluate 3D corrective forces and deformity correction attributable to key parameters of rod contouring in posterior spinal fusion (PSF) for adolescent idiopathic scoliosis (AIS).

Methods

Computerised patient-specific biomechanical models of six AIS cases were used to simulate PSF and evaluate the effects of 5.5-mm cobalt-chrome rod contouring angle (concave–convex angles: 30°−15°, 45°−15° and 60°−15°), length (spanning 4 and 7 vertebrae), and apex location (T7, T9). 3D correction and bone-implant forces were computed and analysed.

Results

By increasing the concave rod contour from 30° to 60°, thoracic kyphosis (TK) increased from 18° ± 2° (15°−19°) to 24° ± 2° (22°−26°), apical vertebra rotation (AVR) correction increased from 41% (SD8%) to 66% (SD18%) whilst the main thoracic curve (MT) correction decreased from 68% (SD6%) to 56% (SD8%). With a contouring length of 4 vs. 7 vertebrae, the resulting TK, AVR and MT corrections were 22° ± 1° (19°−26°) vs. 19° ± 10° (15°−22°), 57% (SD18%) vs. 50% (SD26%) and 59% (SD1%) vs. 69% (SD35%), respectively. With the rod contouring apex at T7 (vs. T9), AVR corrections were 69% (SD19%) vs. 44% (SD9%), with no significant difference in TK and MT corrections, and with comparatively 67% of screw pull-out forces. Corrective forces were more evenly shared with fixation on 7 vs. 4 vertebrae.

Conclusion

Rod contouring of a greater angulation, over a shorter portion of the rod, and more centred at the apex of the main thoracic curve apex improved AVR correction and allowed greater restoration of TK, but resulted in significantly higher screw pull-out forces and came at the expense of less coronal plane correction.

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Data availability

Not applicable for this study.

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Acknowledgements

This project was funded by the Natural Sciences and Engineering Research Council of Canada (PCIPJ-346145-2011; Industrial Research chair with Medtronic of Canada).

Funding

This research was funded by the Natural Sciences and Engineering Research Council of Canada, PCIPJ-346145-2011, Carl-Eric Aubin.

Author information

Authors and Affiliations

  1. Department of Mechanical Engineering, Polytechnique Montreal, PO Box 6079, Downtown station, Montreal, QC, H3C 3A7, Canada

    Marine Gay, Xiaoyu Wang & Carl-Eric Aubin

  2. Sainte-Justine University Hospital Center, 3175 Cote Sainte-Catherine Road, Montreal, QC, H3T 1C5, Canada

    Marine Gay, Xiaoyu Wang & Carl-Eric Aubin

  3. Akron Children’s Hospital, 215 West Bowery Street, Akron, OH, 44308, USA

    Todd Ritzman & Lorena Floccari

  4. Children’s Mercy Hospital, 2401 Gillham Rd, Kansas City, MO, 64112, USA

    Richard M. Schwend

Authors
  1. Marine Gay
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  2. Xiaoyu Wang
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  4. Lorena Floccari
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Contributions

MG: simulations, analysis, interpretation of data for the work, drafting, final approbation, agree to be accountable. XW: design, simulations, analysis, interpretation of the data for the work, drafting work, revising, final approbation, agree to be accountable. TR: interpretation of the data for the work, revising, final approbation, agree to be accountable. LF: interpretation of the data for the work, revising, final approbation, agree to be accountable. RS: recruitment of cases, interpretation of the data for the work, revising, final approbation, agree to be accountable. CÉA: design, supervising the study, interpretation of the data for the work, comprehensive review, final approbation, agree to be accountable.

Corresponding author

Correspondence to Carl-Eric Aubin.

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Conflict of interest

Marine Gay and Xiaoyu Wang: supported by the Natural Sciences and Engineering Research Council of Canada (Industrial Research Chair with Medtronic of Canada). Richard M. Schwend: consultant for Orthopediatrics (outside the scope of the study). Todd Ritzman: grant/research support and consultant for Medtronic, honorarium from Stryker/K2M Spine and stock/shareholder for Apto Orthopaedics (all outside the scope of the study). Lorena Floccari: none. Carl-Éric Aubin: supported by the Natural Sciences and Engineering Research Council of Canada (Industrial Research Chair with Medtronic Canada), and consultant for Medtronic (outside the scope of the study).

Ethical approval

Approval was obtained from the ethics committees of the participating hospitals and of Polytechnique Montreal. The procedures used in this study adhere to the tenets of the Declaration of Helsinki.

Informed consent

Informed consents from the patients and parents were obtained.

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Gay, M., Wang, X., Ritzman, T. et al. Biomechanical analysis of rod contouring in posterior spinal instrumentation and fusion for 3D correction of adolescent idiopathic scoliosis. Spine Deform 11, 1309–1316 (2023). https://doi.org/10.1007/s43390-023-00707-9

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  • DOI: https://doi.org/10.1007/s43390-023-00707-9

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