Screw configuration in proximal humerus plating has a significant impact on fixation failure risk predicted by finite element models

James Fletcher, Markus Windolf, R. Geoff Richards, Boyko Gueorguiev, Peter Varga

Research output: Contribution to journalArticle

Abstract

Background: Proximal humeral fractures occur frequently, with fixed angle locking plates often being used for their treatment. No current quantitative evidence for the effect of different screw configurations exists, and the large number of variations makes biomechanical testing prohibitive. Therefore, we used an established and validated finite element osteosynthesis test kit to quantify the effect of variations in screw configuration on predicted failure risk of PHILOS plate fixation for unstable proximal humerus fractures. Methods: Twenty-six low-density humerus models were osteotomized to create malreduced unstable 3-part fractures that were virtually fixed with PHILOS plates. Twelve screw configurations were simulated: 6 using 2 screw rows, 4 using 3 rows, and 1 with either 8 or 9 screws. Three physiological loading cases were modeled and an established finite element analysis methodology was used. The average peri-screw bone strain, previously demonstrated to predict fatigue cutout failure, was used to compare the different configurations. Results: Significant differences in peri-screw strains, and thus predicted failure risk, were seen with different combinations. The 9-screw configuration demonstrated the lowest peri-screw strains. Fewer screw constructs showed lower strains when placed further apart. The calcar screws (row E) significantly (P < .001) reduced fixation failure risk. Conclusion: Screw configurations significantly impact predicted cutout failure risk for locking plate fixations of unstable proximal humerus fractures in low-density bone. Although requiring clinical corroboration, the result of this study suggests that additional screws reduce peri-screw strains, the distance between them should be maximized whenever possible and the calcar screws should be used.

Original languageEnglish
Pages (from-to)1816-1823
Number of pages8
JournalJournal of Shoulder and Elbow Surgery
Volume28
Issue number9
Early online date26 Apr 2019
DOIs
Publication statusPublished - 1 Sep 2019

Keywords

  • Basic Science Study
  • Computer Modeling
  • PHILOS plate
  • Proximal humerus fracture
  • finite element
  • fixation failure
  • screw configuration

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine

Cite this

Screw configuration in proximal humerus plating has a significant impact on fixation failure risk predicted by finite element models. / Fletcher, James; Windolf, Markus; Richards, R. Geoff; Gueorguiev, Boyko; Varga, Peter.

In: Journal of Shoulder and Elbow Surgery, Vol. 28, No. 9, 01.09.2019, p. 1816-1823.

Research output: Contribution to journalArticle

Fletcher, James ; Windolf, Markus ; Richards, R. Geoff ; Gueorguiev, Boyko ; Varga, Peter. / Screw configuration in proximal humerus plating has a significant impact on fixation failure risk predicted by finite element models. In: Journal of Shoulder and Elbow Surgery. 2019 ; Vol. 28, No. 9. pp. 1816-1823.
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abstract = "Background: Proximal humeral fractures occur frequently, with fixed angle locking plates often being used for their treatment. No current quantitative evidence for the effect of different screw configurations exists, and the large number of variations makes biomechanical testing prohibitive. Therefore, we used an established and validated finite element osteosynthesis test kit to quantify the effect of variations in screw configuration on predicted failure risk of PHILOS plate fixation for unstable proximal humerus fractures. Methods: Twenty-six low-density humerus models were osteotomized to create malreduced unstable 3-part fractures that were virtually fixed with PHILOS plates. Twelve screw configurations were simulated: 6 using 2 screw rows, 4 using 3 rows, and 1 with either 8 or 9 screws. Three physiological loading cases were modeled and an established finite element analysis methodology was used. The average peri-screw bone strain, previously demonstrated to predict fatigue cutout failure, was used to compare the different configurations. Results: Significant differences in peri-screw strains, and thus predicted failure risk, were seen with different combinations. The 9-screw configuration demonstrated the lowest peri-screw strains. Fewer screw constructs showed lower strains when placed further apart. The calcar screws (row E) significantly (P < .001) reduced fixation failure risk. Conclusion: Screw configurations significantly impact predicted cutout failure risk for locking plate fixations of unstable proximal humerus fractures in low-density bone. Although requiring clinical corroboration, the result of this study suggests that additional screws reduce peri-screw strains, the distance between them should be maximized whenever possible and the calcar screws should be used.",
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