James W A Fletcher1, Verena Neumann2, Lisa Wenzel3, Boyko Gueorguiev2, R Geoff Richards2, Harinderjit S Gill4, Michael R Whitehouse5, Ezio Preatoni6. 1. Department for Health, University of Bath, Bath, UK; AO Research Institute Davos, Davos, Switzerland. Electronic address: jwaf20@bath.ac.uk. 2. AO Research Institute Davos, Davos, Switzerland. 3. AO Research Institute Davos, Davos, Switzerland; Department of Trauma Surgery, Trauma Center Murnau, Professor-Küntscher-Str. 8, 82418 Murnau, Germany. 4. Department of Mechanical Engineering, University of Bath, Bath, UK. 5. Musculoskeletal Research Unit, Translational Health Sciences, Bristol Medical School, 1st Floor Learning & Research Building, Southmead Hospital, Bristol, UK; National Institute for Health Research Bristol Biomedical Research Centre, University Hospitals Bristol NHS Foundation Trust and University of Bristol, Bristol, UK. 6. Department for Health, University of Bath, Bath, UK.
Abstract
BACKGROUND: Screws are the most commonly inserted orthopaedic implants. However, several variables related to screw insertion and tightening have not been evaluated. This study aimed firstly to assess the effect of insertion variables on screw tightness, secondly to improve methodologies used by researchers when testing screw insertion techniques and thirdly to assess for any learning or fatigue effects when inserting screws. METHODS: Two surgeons tightened a total of 2280 non-locking, 3.5 mm cortical screws, with 120 screws inserted to what they felt to be optimum tightness whilst varying each of the following factors: different screwdrivers for measuring torque, screwdriver orientation, gloves usage, dominant/non-dominant hand usage, awareness to the applied torque (blinded, unblinded and re-blinded), four bone densities and seven cortical thicknesses. Screws were tightened to failure to determine stripping torque, which was used to calculate screw tightness - ratio between stopping and stripping torque. FINDINGS: Screw tightness increased with glove usage, being blinded to the applied torque and with denser artificial bone and with thinner cortices. Considering all the insertions performed, the two surgeons stopped tightening screws at difference values of tightness ((77% versus 66% (p < 0.001)). A learning effect was observed with some parameters including sterile gloves usage and non-dominant hand application. INTERPRETATION: Different insertion conditions frequently changed screw tightness for both surgeons. Given the influence of screw tightness on fixation stability, the variables investigated within this study should be carefully reported and controlled when performing biomechanical testing alongside practicing screw insertion under different conditions during surgical training.
BACKGROUND: Screws are the most commonly inserted orthopaedic implants. However, several variables related to screw insertion and tightening have not been evaluated. This study aimed firstly to assess the effect of insertion variables on screw tightness, secondly to improve methodologies used by researchers when testing screw insertion techniques and thirdly to assess for any learning or fatigue effects when inserting screws. METHODS: Two surgeons tightened a total of 2280 non-locking, 3.5 mm cortical screws, with 120 screws inserted to what they felt to be optimum tightness whilst varying each of the following factors: different screwdrivers for measuring torque, screwdriver orientation, gloves usage, dominant/non-dominant hand usage, awareness to the applied torque (blinded, unblinded and re-blinded), four bone densities and seven cortical thicknesses. Screws were tightened to failure to determine stripping torque, which was used to calculate screw tightness - ratio between stopping and stripping torque. FINDINGS: Screw tightness increased with glove usage, being blinded to the applied torque and with denser artificial bone and with thinner cortices. Considering all the insertions performed, the two surgeons stopped tightening screws at difference values of tightness ((77% versus 66% (p < 0.001)). A learning effect was observed with some parameters including sterile gloves usage and non-dominant hand application. INTERPRETATION: Different insertion conditions frequently changed screw tightness for both surgeons. Given the influence of screw tightness on fixation stability, the variables investigated within this study should be carefully reported and controlled when performing biomechanical testing alongside practicing screw insertion under different conditions during surgical training.
Authors: James W A Fletcher; Verena Neumann; Lisa Wenzel; Boyko Gueorguiev; R Geoff Richards; Harinderjit S Gill; Michael R Whitehouse; Ezio Preatoni Journal: J Orthop Surg Res Date: 2021-10-26 Impact factor: 2.359