Stripping torques in human bone can be reliably predicted prior to screw insertion with optimum tightness being found between 70% and 80% of the maximum

Bone & Joint Research

article

James W. A. Fletcher¹  Ivan Zderic²  Boyko Gueorguiev²  R. Geoff Richards²  Harinderjit S. Gill³  Michael R. Whitehouse⁴  Ezio Preatoni¹ 

[1] Department for Health, University of Bath;AO Research Institute Davos;Department of Mechanical Engineering, University of Bath;Musculoskeletal Research Unit, Translational Health Sciences, Bristol Medical School, Southmead Hospital

关键词: Screw fixation;    Torque;    Stripping;    Optimum tightness;    Non-locking screw;   

DOI  :  10.1302/2046-3758.98.BJR-2019-0318.R1

学科分类：骨科学

来源: British Editorial Society Of Bone And Joint Surgery

【 摘 要 】

AimsTo devise a method to quantify and optimize tightness when inserting cortical screws, based on bone characterization and screw geometry.MethodsCortical human cadaveric diaphyseal tibiae screw holes (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 recording of compression generated during tightening. Once the target torque had been achieved, immediate pullout testing was performed.ResultsCortical thickness predicted Tstr (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 up to 80% of the maximum (R2 = 0.495; p < 0.001). Beyond 80%, further tightening generated no increase in compression. Pullout force did not change with variations in submaximal tightness beyond 40% of Tstr (R2 = 0.014; p = 0.175).ConclusionScrew tightening between 70% and 80% of the predicted maximum generated optimum compression and pullout forces. Further tightening did not considerably increase compression, made no difference to pullout, and increased the risk of the screw holes being stripped. While further work is needed for development of intraoperative methods for accurate and reliable prediction of the maximum tightness for a screw, this work justifies insertion torque being considerably below the maximum.

【 授权许可】

CC BY-NC