Comparison of the resistance of miniplates and microplates to various in vitro forces

A comparison of the Luhr Mini System (Howmedica, Inc, Rutherford, NJ) and the Luhr Micro System (Howmedica, Inc) was undertaken to determine resistance to various forces using a biomechanical model. Miniplates and microplates were first tested to determine their resistance to forces of displacement on flat bend, edge bend, tension, and compression generated by a materials testing system machine. Then, miniplates and microplates were attached to fresh porcine ribs, fixed to a custom-made jig, and subjected to the same forces of displacement. The load was applied to the bone plate to permanent deformation in all tests. The mini and microplate systems resisted 14.50 and 1.14 kg, respectively, on edgewise bending, 2.65 and 1.10 kg, respectively, on flat bending, 92.03 and 16.44 kg, respectively, on tension, and 127.9 and 27.02 kg, respectively, on compression. The mini and microsystem biomechanical model resisted 1.89 and 0.94 kg, respectively, on edgewise bending, 5.20 and 0.85 kg, respectively, on flat bending, 37.60 and 15.72 kg, respectively, on tension, and 53.55 and 16.0 kg, respectively, on compression. The results suggest that the Luhr Mini Fixation System provides a significant amount of resistance to tensile and compressive forces, but is weakest when large forces are applied at 90 degrees to the flat portion of the plate. The system showed decreased force resistance in the biomechanical model except on flat bending. The Luhr Micro Fixation System has significantly less resistance to deformation, but shows no decrease in ability to resist forces of displacement in the biomechanical model.