Deviations in positioning variable pitch screws- scaphoid waist fractures

Abstract

IntroductionOperative therapy using a headless cannulated variable pitch compression screw is the gold standard for the treatment of instable scaphoid fractures. HypothesisDeviation from the central placement is associated with a loss of stability and stiffness. Material and methodsAn artificial bone model was manufactured and different screw positions (central, 10° and 20° to the long axis) were assessed. A shearing test with axial force on the 45° flexed scaphoid was applied. ResultsThe inserted variable pitch screw showed the highest stiffness and failure force in a position in the long axis. At 10 degrees, a slight decrease in stiffness (32.7N/mm±9.3N/mm) and failure force (41.6N±13.2N) was observed, while a significant reduction in stiffness (29.3N/mm±4.6N/mm) and failure force (50.3N±19.5N) was measured at 20 degrees. DiscussionDeviations in the angle of insertion of the compression screw cause loss in failure force, thus deviations from the central placement is associated with less stability and stiffness. Level of proofControlled laboratory study (basic science study, biomechanical testing).