What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?

James Fletcher, Ivan Zderic, Boyko Gueorguiev, R. Geoff Richards, Richie Gill, Michael Whitehouse, Ezio Preatoni

Research output: Contribution to conferencePoster

Abstract

Objectives: The currently used screw insertion techniques are reliant on a surgeon’s subjective feeling of the required and applied torques. In experimental testing, approximately 1 in 4 screws have irreparably damaged the surrounding bone whilst being inserted due to an inability to appreciate the stripping limits, increasing the risk of fixation failure . If maximum and optimum torques could be predicted prior to screw insertion, this could reduce failures, expedite operations and strengthen constructs. The aim of this study was to devise a method to quantify and optimise tightness for the insertion of cortical fracture-fixation screws, based on bone characterisation and screw geometry. Methods: Cortical human diaphyseal tibiae samples (n=20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr) and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n=66) to targeted torques representing 40 to 100% of Tstr, with the compression generated during tightening being measured. Once the target torque had been achieved, immediate pullout testing was performed. Results: Cortical thickness predicted the stripping torque (R2=0.862, P<0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient and screw geometries (R2=0.894, P<0.001). Compression increased with screw tightness – calculated as the ratio of targeted/stripping torque - up to 80% of the maximum (R2=0.495, P<0.001). Beyond 80%, no further tightness generated the same increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2=0.014, P=0.175). Conclusion: Screws tightened to 70 - 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not significantly increase compression, did not improve resistance to pullout and increased the risk of the bone being stripped. Whilst intraoperative methods for accurately and reliably predicting the maximum tightness for a screw are needed, this work justifies controlled insertion considerably below the maximum torque and demonstrates methods to predict the required torque.
Original languageEnglish
Publication statusPublished - Sep 2019
EventBone Research Society and British Orthopaedic Research Society 5th Joint Meeting - Sir Martin Evans Building, School of Biosciences, Cardiff University, Cardiff, UK United Kingdom
Duration: 4 Sep 20196 Sep 2019
https://boneresearchsociety.org/meeting/cardiff2019/

Conference

ConferenceBone Research Society and British Orthopaedic Research Society 5th Joint Meeting
Abbreviated titleBRS/BORS 5th Joint Meeting
CountryUK United Kingdom
CityCardiff
Period4/09/196/09/19
Internet address

Cite this

Fletcher, J., Zderic, I., Gueorguiev, B., Richards, R. G., Gill, R., Whitehouse, M., & Preatoni, E. (2019). What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?. Poster session presented at Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, Cardiff, UK United Kingdom.

What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion? / Fletcher, James; Zderic, Ivan; Gueorguiev, Boyko; Richards, R. Geoff; Gill, Richie; Whitehouse, Michael; Preatoni, Ezio.

2019. Poster session presented at Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, Cardiff, UK United Kingdom.

Research output: Contribution to conferencePoster

Fletcher, J, Zderic, I, Gueorguiev, B, Richards, RG, Gill, R, Whitehouse, M & Preatoni, E 2019, 'What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?' Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, Cardiff, UK United Kingdom, 4/09/19 - 6/09/19, .
Fletcher J, Zderic I, Gueorguiev B, Richards RG, Gill R, Whitehouse M et al. What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?. 2019. Poster session presented at Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, Cardiff, UK United Kingdom.
Fletcher, James ; Zderic, Ivan ; Gueorguiev, Boyko ; Richards, R. Geoff ; Gill, Richie ; Whitehouse, Michael ; Preatoni, Ezio. / What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?. Poster session presented at Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, Cardiff, UK United Kingdom.
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title = "What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?",
abstract = "Objectives: The currently used screw insertion techniques are reliant on a surgeon’s subjective feeling of the required and applied torques. In experimental testing, approximately 1 in 4 screws have irreparably damaged the surrounding bone whilst being inserted due to an inability to appreciate the stripping limits, increasing the risk of fixation failure . If maximum and optimum torques could be predicted prior to screw insertion, this could reduce failures, expedite operations and strengthen constructs. The aim of this study was to devise a method to quantify and optimise tightness for the insertion of cortical fracture-fixation screws, based on bone characterisation and screw geometry. Methods: Cortical human diaphyseal tibiae samples (n=20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr) and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n=66) to targeted torques representing 40 to 100{\%} of Tstr, with the compression generated during tightening being measured. Once the target torque had been achieved, immediate pullout testing was performed. Results: Cortical thickness predicted the stripping torque (R2=0.862, P<0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient and screw geometries (R2=0.894, P<0.001). Compression increased with screw tightness – calculated as the ratio of targeted/stripping torque - up to 80{\%} of the maximum (R2=0.495, P<0.001). Beyond 80{\%}, no further tightness generated the same increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40{\%} of Tstr (R2=0.014, P=0.175). Conclusion: Screws tightened to 70 - 80{\%} of the predicted maximum generated optimum compression and pullout forces. Further tightening did not significantly increase compression, did not improve resistance to pullout and increased the risk of the bone being stripped. Whilst intraoperative methods for accurately and reliably predicting the maximum tightness for a screw are needed, this work justifies controlled insertion considerably below the maximum torque and demonstrates methods to predict the required torque.",
author = "James Fletcher and Ivan Zderic and Boyko Gueorguiev and Richards, {R. Geoff} and Richie Gill and Michael Whitehouse and Ezio Preatoni",
year = "2019",
month = "9",
language = "English",
note = "Bone Research Society and British Orthopaedic Research Society 5th Joint Meeting, BRS/BORS 5th Joint Meeting ; Conference date: 04-09-2019 Through 06-09-2019",
url = "https://boneresearchsociety.org/meeting/cardiff2019/",

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TY - CONF

T1 - What is the optimum tightness for nonlocking cortical screws, and how can this be predicted prior to insertion?

AU - Fletcher, James

AU - Zderic, Ivan

AU - Gueorguiev, Boyko

AU - Richards, R. Geoff

AU - Gill, Richie

AU - Whitehouse, Michael

AU - Preatoni, Ezio

PY - 2019/9

Y1 - 2019/9

N2 - Objectives: The currently used screw insertion techniques are reliant on a surgeon’s subjective feeling of the required and applied torques. In experimental testing, approximately 1 in 4 screws have irreparably damaged the surrounding bone whilst being inserted due to an inability to appreciate the stripping limits, increasing the risk of fixation failure . If maximum and optimum torques could be predicted prior to screw insertion, this could reduce failures, expedite operations and strengthen constructs. The aim of this study was to devise a method to quantify and optimise tightness for the insertion of cortical fracture-fixation screws, based on bone characterisation and screw geometry. Methods: Cortical human diaphyseal tibiae samples (n=20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr) and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n=66) to targeted torques representing 40 to 100% of Tstr, with the compression generated during tightening being measured. Once the target torque had been achieved, immediate pullout testing was performed. Results: Cortical thickness predicted the stripping torque (R2=0.862, P<0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient and screw geometries (R2=0.894, P<0.001). Compression increased with screw tightness – calculated as the ratio of targeted/stripping torque - up to 80% of the maximum (R2=0.495, P<0.001). Beyond 80%, no further tightness generated the same increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2=0.014, P=0.175). Conclusion: Screws tightened to 70 - 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not significantly increase compression, did not improve resistance to pullout and increased the risk of the bone being stripped. Whilst intraoperative methods for accurately and reliably predicting the maximum tightness for a screw are needed, this work justifies controlled insertion considerably below the maximum torque and demonstrates methods to predict the required torque.

AB - Objectives: The currently used screw insertion techniques are reliant on a surgeon’s subjective feeling of the required and applied torques. In experimental testing, approximately 1 in 4 screws have irreparably damaged the surrounding bone whilst being inserted due to an inability to appreciate the stripping limits, increasing the risk of fixation failure . If maximum and optimum torques could be predicted prior to screw insertion, this could reduce failures, expedite operations and strengthen constructs. The aim of this study was to devise a method to quantify and optimise tightness for the insertion of cortical fracture-fixation screws, based on bone characterisation and screw geometry. Methods: Cortical human diaphyseal tibiae samples (n=20) underwent destructive testing to firstly establish the relationship between cortical thickness and experimental stripping torque (Tstr) and secondly to calibrate an equation to predict Tstr. Using the equation’s predictions, 3.5 mm screws were inserted (n=66) to targeted torques representing 40 to 100% of Tstr, with the compression generated during tightening being measured. Once the target torque had been achieved, immediate pullout testing was performed. Results: Cortical thickness predicted the stripping torque (R2=0.862, P<0.001) as did an equation based on tensile yield stress, bone-screw friction coefficient and screw geometries (R2=0.894, P<0.001). Compression increased with screw tightness – calculated as the ratio of targeted/stripping torque - up to 80% of the maximum (R2=0.495, P<0.001). Beyond 80%, no further tightness generated the same increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2=0.014, P=0.175). Conclusion: Screws tightened to 70 - 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not significantly increase compression, did not improve resistance to pullout and increased the risk of the bone being stripped. Whilst intraoperative methods for accurately and reliably predicting the maximum tightness for a screw are needed, this work justifies controlled insertion considerably below the maximum torque and demonstrates methods to predict the required torque.

M3 - Poster

ER -