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A novel scoliosis instrumentation using special superelastic nickel–titanium shape memory rods: a biomechanical analysis using a calibrated computer model and data from a clinical trial

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

Abstract

Study design

Biomechanical analysis of scoliosis instrumentation using superelastic Nickel–titanium shape memory (SNT) rods.

Objective

To compare SNT with conventional Titanium (Ti) and Cobalt–chrome (Co–Cr) rods.

Summary of background data

A clinical trial has documented comparable efficacy between two adolescent idiopathic scoliosis (AIS) cohorts instrumented using SNT versus conventional Ti rods. The shape memory and superelasticity of the SNT rod are thought to allow easy rod insertion, progressive curve correction, and correction from spinal tissue relaxation, but study is yet to be done to assess the effects of the shape memory and superelasticity.

Methods

Instrumentations of AIS patients from the clinical trial were computationally simulated using SNT, Ti and Co–Cr rods (5.5 or 6 mm; 30°, 50° or 60° sagittal contouring angles; 0°, 25° or 50° coronal over-contouring angles). Curve correction, its improvement from stress relaxation in the spine, and loads in the instrumentation constructs were computed and compared.

Results

The simulated main thoracic Cobb angles (MT) and thoracic kyphosis with the SNT rods were 4°–7° higher and 1°–2° lower than the Ti and Co–Cr rods, respectively. Bone–implant forces with Ti and Co–Cr rods were higher than the SNT rods by 84% and 130% at 18 °C and 35% and 65% at 37 °C, respectively (p < 0.001). Further corrections of the MT from the simulated stress relaxation in the spine were 4°–8° with the SNT rods versus 2°–5° with the Ti and Co–Cr rods (p < 0.001).

Conclusion

This study concurs with clinical observation that the SNT rods are easier to insert and can result in similar correction to the conventional rods. The SNT rods allow significantly lower bone–implant forces and have the ability to take advantage of post-instrumentation correction as the tissues relax.

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Funding

This study was financially supported by the Natural Sciences and Engineering Research Council of Canada (Industrial Research Chair program with Medtronic of Canada, IRCPJ 346145-16) and the Scoliosis Research Society (9667002).

Author information

Authors and Affiliations

  1. Department of Mechanical Engineering, Polytechnique Montreal, Downtown Station, P.O. Box 6079, Montreal, QC, H3C 3A7, Canada

    Xiaoyu Wang & Carl-Eric Aubin

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

    Xiaoyu Wang & Carl-Eric Aubin

  3. Department of Orthopaedics and Traumatology, The University of Hong Kong, Hong Kong SAR, China

    Kelvin Yeung, Jason Pui Yin Cheung, Johnson Yiu-Nam Lau, Weichen Qi & Kenneth Man-Chee Cheung

Authors
  1. Xiaoyu Wang
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  2. Kelvin Yeung
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  5. Weichen Qi
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  6. Kenneth Man-Chee Cheung
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  7. Carl-Eric Aubin
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Contributions

XW: Substantial contributions to the design of the work, the analysis and interpretation of the results, drafting and revising it critically for important intellectual content, and the final approval of the submitted version. KY: Substantial contributions to the acquisition and interpretation of data for the work, drafting and revising it critically for important intellectual content, and the final approval of the submitted version. JPYC: Substantial contributions to the acquisition and interpretation of data for the work, drafting and revising it critically for important intellectual content, and the final approval of the submitted version. JY-NL: Substantial contributions to drafting and revising the work critically for important intellectual content, and the final approval of the submitted version. WQ: Substantial contributions to the acquisition and interpretation of data for the work and the final approval of the submitted version. KM-CC: Substantial contributions to the design of the work, the interpretation of the results, drafting and revising it critically for important intellectual content, and the final approval of the submitted version. C-EA: Substantial contributions to the design of the work, the interpretation of the results, drafting and revising it critically for important intellectual content, and the final approval of the submitted version.

Corresponding authors

Correspondence to Kenneth Man-Chee Cheung or Carl-Eric Aubin.

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Approval of Research Ethics Committee was obtained to conduct this study.

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Wang, X., Yeung, K., Cheung, J.P.Y. et al. A novel scoliosis instrumentation using special superelastic nickel–titanium shape memory rods: a biomechanical analysis using a calibrated computer model and data from a clinical trial. Spine Deform 8, 369–379 (2020). https://doi.org/10.1007/s43390-020-00075-8

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  • DOI: https://doi.org/10.1007/s43390-020-00075-8

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