To determine the metal plate that has almost the same volume and weight as the conventional plate, but has improved properties by changing the shape using finite element analysis.

The bone is assumed to be of 100 mm length, 20 mm outer diameter and 12 mm inner diameter, respectively. There is a fracture line that is perpendicular to the major axis of the bone at the center. The two pieces of bone are joined together using a metallic plate that is made of titanium. Six holes are located, with an interval of 12 mm. We suppose that screws of 2 mm diameter and 25 mm length are inserted in six holes. The metallic plates are of 5 shapes (A, B, C, D and E) in total. Shape A is the standard or nominal type. Shape B and C are thicker at the center of the plate, respectively. Shape D and E are wider at the center. Six types of load are applied to each of those plates: tension, compression, anterior flexion, posterior flexion, lateral flexion and torsion. We compared stress, deformation, maximal stress and maximal deformation, according to the six types of load.

Our deliberate investigation using finite element analysis showed that increasing the thickness or width at the center of metallic plates lowered the maximum stress and deformation. In particular, maximal stress and deformation could be reduced by 33.5% and 38.6%, respectively, in the anterior bending situation. Compression showed lower stress and deformation in type C or D, but the absolute quantity was much smaller than others, for example 0.01-0.001 times.

As for the internal bone fixation plates with the same volume, the wider or thicker in the middle the plate become, the less deformation and yielding it bears.