The strength of polyaxial locking interfaces of distal radius plates.
BACKGROUND
Currently available polyaxial locking plates represent the consequent enhancement of fixed-angle, first-generation locking plates. In contrast to fixed-angle locking plates which are sufficiently investigated, the strength of the new polyaxial locking options has not yet been evaluated biomechanically. This study investigates the mechanical strength of single polyaxial interfaces of different volar radius plates.


METHODS
Single screw-plate interfaces of the implants Palmar 2.7 (Königsee Implantate und Instrumente zur Osteosynthese GmbH, Allendorf, Germany), VariAx (Stryker Leibinger GmbH & Co. KG, Freiburg, Germany) und Viper (Integra LifeSciences Corporation, Plainsboro, NJ, USA) were tested by cantilever bending. The strength of 0 degrees, 10 degrees and 20 degrees screw locking angle was obtained during static and dynamic loading.


RESULTS
The Palmar 2.7 interfaces showed greater ultimate strength and fatigue strength than the interfaces of the other implants. The strength of the VariAx interfaces was about 60% of Palmar 2.7 in both, static and dynamic loading. No dynamic testing was applied to the Viper plate because of its low ultimate strength. By static loading, an increase in screw locking angle caused a reduction of strength for the Palmar 2.7 and Viper locking interfaces. No influence was observed for the VariAx locking interfaces. During dynamic loading; angulation had no influence on the locking strength of Palmar 2.7. However, reduction of locking strength with increasing screw angulation was observed for VariAx.


CONCLUSIONS
The strength of the polyaxial locking interfaces differs remarkably between the examined implants. Depending on the implant an increase of the screw locking angle causes a reduction of ultimate or fatigue strength, but not in all cases a significant impact was observed.
Hoffmeier
Konrad L
KL
Universitätsklinikum Jena, Department of Trauma, Hand and Reconstructive Surgery, ErlangerAllee 101, D-07747 Jena, Germany. Konrad.Hoffmeier@med.uni-jena.de
Hofmann
Gunther O
GO
Mückley
Thomas
T
D001860:Bone Plates; D001863:Bone Screws; D019245:Compressive Strength; D019544:Equipment Failure Analysis; D006801:Humans; D011474:Prosthesis Design; D011884:Radius / Q000601:surgery*; D013718:Tensile Strength