Non-locking screw insertion

No benefit seen if tightness exceeds 80% of the maximum torque

James W A Fletcher, Beate Ehrhardt, Alisdair MacLeod, Michael R Whitehouse, Harinderjit Gill, Ezio Preatoni

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

BACKGROUND: Millions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength.

METHODS: Longitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100% of the theoretical stripping torque (Tstr) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing.

FINDINGS: Screw-bone compression increased linearly with applied torque up to 80% of Tstr (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength.

INTERPRETATION: Increasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below Tstr, did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs.

Original languageEnglish
Pages (from-to)40-45
Number of pages6
JournalClinical Biomechanics
Volume70
Early online date9 Jul 2019
DOIs
Publication statusE-pub ahead of print - 9 Jul 2019

Keywords

  • Compression
  • Fixation failure
  • Insertion torque
  • Pullout force
  • Tightness

ASJC Scopus subject areas

  • Biophysics
  • Orthopedics and Sports Medicine

Cite this

Non-locking screw insertion : No benefit seen if tightness exceeds 80% of the maximum torque. / Fletcher, James W A; Ehrhardt, Beate; MacLeod, Alisdair; Whitehouse, Michael R; Gill, Harinderjit; Preatoni, Ezio.

In: Clinical Biomechanics, Vol. 70, 01.12.2019, p. 40-45.

Research output: Contribution to journalArticle

@article{05e46486bf834f78a90a7395150d8f95,
title = "Non-locking screw insertion: No benefit seen if tightness exceeds 80{\%} of the maximum torque",
abstract = "BACKGROUND: Millions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength.METHODS: Longitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100{\%} of the theoretical stripping torque (Tstr) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing.FINDINGS: Screw-bone compression increased linearly with applied torque up to 80{\%} of Tstr (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength.INTERPRETATION: Increasing screw tightness beyond 80{\%} of the maximum did not increase screw-bone compression. Variations in torques below Tstr, did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs.",
keywords = "Compression, Fixation failure, Insertion torque, Pullout force, Tightness",
author = "Fletcher, {James W A} and Beate Ehrhardt and Alisdair MacLeod and Whitehouse, {Michael R} and Harinderjit Gill and Ezio Preatoni",
note = "Copyright {\circledC} 2019. Published by Elsevier Ltd.",
year = "2019",
month = "7",
day = "9",
doi = "10.1016/j.clinbiomech.2019.07.009",
language = "English",
volume = "70",
pages = "40--45",
journal = "Clinical Biomechanics",
issn = "0268-0033",
publisher = "Elsevier",

}

TY - JOUR

T1 - Non-locking screw insertion

T2 - No benefit seen if tightness exceeds 80% of the maximum torque

AU - Fletcher, James W A

AU - Ehrhardt, Beate

AU - MacLeod, Alisdair

AU - Whitehouse, Michael R

AU - Gill, Harinderjit

AU - Preatoni, Ezio

N1 - Copyright © 2019. Published by Elsevier Ltd.

PY - 2019/7/9

Y1 - 2019/7/9

N2 - BACKGROUND: Millions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength.METHODS: Longitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100% of the theoretical stripping torque (Tstr) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing.FINDINGS: Screw-bone compression increased linearly with applied torque up to 80% of Tstr (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength.INTERPRETATION: Increasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below Tstr, did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs.

AB - BACKGROUND: Millions of non-locking screws are manually tightened during surgery each year, but their insertion frequently results in overtightening and damage to the surrounding bone. We postulated that by calculating the torque limit of a screw hole, using bone and screw properties, the risk of overtightening during screw insertion could be reduced. Additionally, predicted maximum torque could be used to identify optimum screw torque, as a percentage of the maximum, based on applied compression and residual pullout strength.METHODS: Longitudinal cross-sections were taken from juvenile bovine tibial diaphyses, a validated surrogate of human bone, and 3.5 mm cortical non-locking screws were inserted. Fifty-four samples were used to define the association between stripping torque and cortical thickness. The relationship derived enabled prediction of insertion torques representing 40 to 100% of the theoretical stripping torque (Tstr) for a further 170 samples. Screw-bone compression generated during insertion was measured, followed immediately by axial pullout testing.FINDINGS: Screw-bone compression increased linearly with applied torque up to 80% of Tstr (R2 = 0.752, p < 0.001), but beyond this, no significant further compression was generated. After screw insertion, with all screw threads engaged, more tightening did not create any significant (R2 = 0.000, p = 0.498) increase in pullout strength.INTERPRETATION: Increasing screw tightness beyond 80% of the maximum did not increase screw-bone compression. Variations in torques below Tstr, did not affect pullout forces of inserted screws. Further validation of these findings in human bone and creation of clinical guidelines based on this research approach should improve surgical outcomes and reduce operative costs.

KW - Compression

KW - Fixation failure

KW - Insertion torque

KW - Pullout force

KW - Tightness

UR - http://www.scopus.com/inward/record.url?scp=85070108125&partnerID=8YFLogxK

U2 - 10.1016/j.clinbiomech.2019.07.009

DO - 10.1016/j.clinbiomech.2019.07.009

M3 - Article

VL - 70

SP - 40

EP - 45

JO - Clinical Biomechanics

JF - Clinical Biomechanics

SN - 0268-0033

ER -