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Biomechanical effect of pedicle screw distribution in AIS instrumentation using a segmental translation technique: computer modeling and simulation

Xiaoyu Wang, A. Noelle Larson, Dennis G. Crandall, Stefan Parent, Hubert Labelle, Charles G. T. Ledonio and Carl-Éric Aubin

Article (2017)

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Cite this document: Wang, X., Larson, A. N., Crandall, D. G., Parent, S., Labelle, H., Ledonio, C. G. T. & Aubin, C.-É. (2017). Biomechanical effect of pedicle screw distribution in AIS instrumentation using a segmental translation technique: computer modeling and simulation. Scoliosis and Spinal Disorders, 12. doi:10.1186/s13013-017-0120-4
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Abstract

BACKGROUND: Efforts to select the appropriate number of implants in adolescent idiopathic scoliosis (AIS) instrumentation are hampered by a lack of biomechanical studies. The objective was to biomechanically evaluate screw density at different regions in the curve for AIS correction to test the hypothesis that alternative screw patterns do not compromise anticipated correction in AIS when using a segmental translation technique. METHODS: Instrumentation simulations were computationally performed for 10 AIS cases. We simulated simultaneous concave and convex segmental translation for a reference screw pattern (bilateral polyaxial pedicle screws with dorsal height adjustability at every level fused) and four alternative patterns; screws were dropped respectively on convex or concave side at alternate levels or at the periapical levels (21 to 25% fewer screws). Predicted deformity correction and screw forces were compared. RESULTS: Final simulated Cobb angle differences with the alternative screw patterns varied between 1 degrees to 5 degrees (39 simulations) and 8 degrees (1 simulation) compared to the reference maximal density screw pattern. Thoracic kyphosis and apical vertebral rotation were within 2 degrees of the reference screw pattern. Screw forces were 76 +/- 43 N, 96 +/- 58 N, 90 +/- 54 N, 82 +/- 33 N, and 79 +/- 42 N, respectively, for the reference screw pattern and screw dropouts at convex alternate levels, concave alternate levels, convex periapical levels, and concave periapical levels. Bone-screw forces for the alternative patterns were higher than the reference pattern (p < 0.0003). There was no statistical bone-screw force difference between convex and concave alternate dropouts and between convex and concave periapical dropouts (p > 0.28). Alternate dropout screw forces were higher than periapical dropouts (p < 0.05). CONCLUSIONS: Using a simultaneous segmental translation technique, deformity correction can be achieved with 23% fewer screws than maximal density screw pattern, but resulted in 25% higher bone-screw forces. Screw dropouts could be either on the convex side or on the concave side at alternate levels or at periapical levels. Periapical screw dropouts may more likely result in lower bone-screw force increase than alternate level screw dropouts.

Uncontrolled Keywords

Adolescent idiopathic scoliosis; Biomechanical modeling; Instrumentation; Pedicle screw; Screw density; Screw distribution; Screw pattern; Simulation

Open Access document in PolyPublie
Subjects: 1900 Génie biomédical > 1903 Biomécanique
2100 Génie mécanique > 2100 Génie mécanique
9000 Sciences de la santé > 9000 Sciences de la santé
Department: Département de génie mécanique
Research Center: Non applicable
Funders: CRSNG / NSERC, Scoliosis Research Society
Date Deposited: 09 Mar 2020 16:07
Last Modified: 10 Mar 2020 01:20
PolyPublie URL: https://publications.polymtl.ca/3597/
Document issued by the official publisher
Journal Title: Scoliosis and Spinal Disorders (vol. 12)
Publisher: Springer Nature
Official URL: https://doi.org/10.1186/s13013-017-0120-4

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