Syndesmosis Fixation: Analysis of Shear Stress via Axial Load on 3.5-mm and 4.5-mm Quadricortical Syndesmotic Screws

The effect of shear stress on a fixated distal syndesmosis of the ankle was evaluated with a servohydraulic materials–testing machine. Eighteen syndesmoses were fixated in a quadricortical technique using 3.5-mm cortical and 4.5-mm cortical stainless steel screws. A shear stress was applied via an axial load in an attempt to simulate weightbearing. The 4.5-mm quadricortical screws produced a higher yield load and peak load (484.3 ± 93.8 N and 597.7 ± 81.4 N) when compared with the 3.5-mm quadricortical syndesmotic screws (412.8 ± 55 N, P = .033 and 511.2 ± 64.4 N). These findings suggest that a larger diameter screw provides greater resistance to an applied shear stress at the distal syndesmosis.