"Turn-of-the-nut" method is not appropriate for use in cancellous bone

Melissa Ryan, Aaron Mohtar, John Costi, Karen Reynolds

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)

    Abstract

    Objective: The level to which bone screws are tightened is determined subjectively by the operating surgeon. It is likely that the tactile feedback that surgeons rely on is based on localized tissue yielding, which may predispose the screw-bone interface to failure. A limited number of studies have investigated the ratio between clinical tightening torque and stripping torque. The purpose of this study was to measure, for the first time, the ratio between yield torque (T yield) and stripping torque (T max) during screw insertion into the cancellous bone and to compare these torques with clinical levels of tightening reported in the literature. Additionally, a rotational limit was investigated as a potential end point for screw insertion in cancellous bone. Methods: A 6.5-mm outer diameter commercial cancellous bone screw was inserted into human femoral head specimens (n 89). Screws were inserted to failure, while recording insertion torque, compression under the screw head, and rotation angle. Results: The median, interquartile ranges, and coefficient of variation were calculated for each of the following parameters: T yield, T max, T yield /T max, slope, T plateau, and rotation angle. The median ratio of T yield /T max and rotation angle was 85.45% and 96.5 degrees, respectively. The coefficient of variation was greatest for the rotation angle compared with the ratio of T yield /T max (0.37 vs. 0.12). Conclusions: The detection of yield may be a more precise method than the rotation angle in cancellous bone; however, bone-screw constructs that exhibit a T yield close to T max may be more susceptible to stripping during insertion. Future work can identify factors that influence the ratio of T yield /T max may help to reduce the incidence of screw stripping. ©

    Original languageEnglish
    Pages (from-to)e437-e441
    Number of pages5
    JournalJournal of Orthopaedic Trauma
    Volume29
    Issue number11
    DOIs
    Publication statusPublished - 1 Nov 2015

    Keywords

    • cancellous bone
    • insertion torque
    • screw stripping
    • stripping torque
    • yield torque

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