Is Unicortical Locking Screw Placement Effective For The Torsional Loads in the Distal Radius Fractures? : Biomechanical Study in Cadaver

Abstract

Background We aimed to compare biomechanical outcomes of short-length (75%-length) and full-length (100%-length) unicortical distal screws under axial and torsional compression in cadaveric distal radius volar plate model. Methods A total of 20 wrists from 10 fresh frozen cadavers were included. 2.5 mm titanium alloy distal radius anatomical plates was placed to the distal radii in full anatomical position, just proximal to the watershed line. Three bicortical screws to the shaft of the radius, followed by unicortical drilling for distal screwing were placed. Measurement by pulling the drill once it reached the opposite cortex was applied. We selected the screw lengths such that they corresponded to the 75% of the measured length (short-length). In the same configuration for each of the cadavers, we delivered six screws from distal radius holes of the anatomical plate. oscillating handsaw was used to create extraarticular distal radius fracture model (AO 23-A3.2). We created dorsal AP model by performing a 1-cm wedge osteotomy from dorsal aspect. Complete separation of the volar cortex was achieved. Potting was performed by embedding the shaft of the prepared radius into the polyurethane medium. We placed aluminum apparatus into the distal end to ensure applying of torsional and axial loading in biomechanistic tests. Results No statistically significant difference of stiffness between the short-length and full-length distal screws both under axial compression(p = 0.88) and torsional compression (p = 0.82). Short-length and full-length distal screw groups did not differ in elastic limit under axial compression (p = 0.71) and torsional compression (p = 0.71). Maximal force on short-length and full-length distal screw groups were also similar under both axial compression (p = 0.71) and torsional compression (p = 0.50). Conclusion It is a safe method under torsional load to avoid drilling of the dorsal cortex and unicortical delivery of 75%-length distal screws could be performed in order to prevent from extensor tendon complications secondary to drilling or screw protrusion.