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The impact of countersinking headless compression screws on fracture compression in 3 fracture topologies: When Ship-to-Shore Matters More
Spencer B Chambers, MD
1; Daniel Thompson, MS
2; Michael B. Gottschalk, MD
3; Eric R. Wagner, MD
3; Nina Suh, MD
31Western University, Roth | McFarlane Hand and Upper Limb Centre, London, ON, Canada; 2Emory Univeristy, Atlanta, GA; 3Emory University School of Medicine, Atlanta, GA
IntroductionScaphoid fractures are commonly fixated with headless compression screws. These devices generate intrinsic compression that is dependent on the bone screw interface at the proximal and distal segment as well as depth of insertion. To minimize the risk of prominent hardware, screws are sunk beneath chondral surfaces, but minimally invasive techniques necessitate indirect measurements of screw depth with fluoroscopy, making it difficult to determine how far a screw has been advanced, which may impact fixation. The purpose of this study is to characterize fracture compression with countersinking in three fracture arrangements for a fully threaded headless compression screw.
Materials & MethodsTests were performed on three Sawbones fracture models and two insertion techniques. The fracture models representing proximal, waist, and distal fractures were composed of a top foam sheet of varying thickness (10mm, 14mm, 18mm) and bottom sheet (25mm) spaced 2mm apart. Both insertion techniques utilized an 30mm Acumed Acutrak 2 Mini screw inserted with a force of 35N at 30 revolutions per minute. Flush insertion was concluded when the screw head was level with the top block, and countersunk insertion was concluded when the screw head was 2mm beneath the top block surface. This process was completed five times in each configuration, for a total of 30 tests. Descriptive statistics were reported and comparisons between groups were performed using paired Student's T-Tests with significance set at p=0.05.
ResultsFracture compression did not differ when countersinking the screw in models of proximal or waist fractures (p>0.05) but dropped significantly in the model of distal fracture model (p<0.05). Driving torque was similar regardless of screw position or fracture model (p>0.05).
ConclusionsThere is a higher risk of compression loss during countersinking of headless compression screws when the distal fragment is small. When using variable pitch headless compression screws for fracture fixation picking a trajectory where the smaller fragment is entered first (ship-to-shore orientation) is advisable to minimize the risk of compression loss with device countersinking. If this is not possible, judicious advancement of the screw is recommended to minimize the risk of losing compression.
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