The Fixation Strength of Scaphoid Bone Screws: An In Vitro Investigation Using Polyurethane Foam

PurposeTo compare the compression strength and pull-apart resistance of 5 single-piece scaphoid bone compression screws (Acutrak, Asnis, Herbert, Herbert-Whipple, and Little Grafter), with those of 2 dual-component screws (Kompressor and TwinFix).MethodsTwo blocks of polyurethane foam were compressed with a screw while held in a tension test machine, with the force measured at full insertion of the screw. The 2 blocks were then pulled apart, and the maximum resistive force was measured.ResultsThe dual-component screws (Kompressor and TwinFix) gave greater compression force than the single-component screws, with the Kompressor screw giving statistically significantly greater compression than the TwinFix. The pull-apart resistance forces did not show such clear differences.ConclusionsThe Kompressor screw achieves the greatest compressive forces and has one of the highest pull-apart forces.Clinical relevanceWhen compression and pull-apart resistance are considered, the Kompressor screw has advantages over other methods of scaphoid fixation.