Are there any differences in various polyaxial locking systems? A mechanical study of different locking screws in multidirectional angular stable distal radius plates.

Numerous angular stable plates for the distal radius exist, and technically based comparisons of the polyaxial locking interfaces are lacking. The aim of this mechanical study was to investigate three different locking interfaces of angular stable volar plates by cantilever bending: VA-LCP Two-Column Distal Radius Plates 2.4 mm (Synthes (R) GmbH, Oberdorf, Switzerland), IXOS (R) P4 (Martin, Tuttlingen, Germany) and VariAX (TM) (Stryker, Duisburg, Germany). We assessed the strength of 0 degrees, 50 degrees, 10 degrees and 15 degrees screw locking angles and tested the bending strength from 10 degrees to 50 degrees angles by cyclic loading until breakage. The final setup repeated the above assessments by inclusion of four locking screws. The single screw-plate interfaces of the VA-LCP showed the highest bending moment at an angle of 0 degrees and 5 degrees, the IXOS P4 at an angle of 10 degrees and 15 degrees and the VariAX" when changing the insertion angle from 10 degrees into 5 degrees. The strength of polyaxial locking interfaces and mechanism of failure proved to be different among the examined plates.