A finite element analysis of the trapezoidal plate. How to get a stable fixation at different fracture lines?

The fractures in the condylar area are a challenge for every surgeon, for the treatment of which trapezoidal condylar plate is used in most cases. However, it is not possible to position the plate in the ideal osteosynthesis lines according to Meyer et al. in every clinical situation. In many cases, the fracture line is also not in the centre of the trapezoidal plate. The aim of this study is to investigate the osteosynthesis rigidity and the effect of plate localisation relative to the fracture line.

In a simulation model in the first group the plate was positioned in the ideal position in the middle of the condylar base, in the second group the plate position was changed - the plate was shifted upwards until the fracture passed underneath the centre of the plate again and in the last group the plate was moved further down so that the fracture passes underneath the middle of the plate. Heterogeneity of the bone was simulated using different sets of biomechanical properties.

In the experiment, the joints were fully constrained and a force of 500 N was applied to the opposite side. An interaction between bone and plate was completely excluded and the stability of the plates as well as the mobility of the bone fragments was analysed.

The results have shown that an inferior position of the fracture line leads to greater mobility of the fragments if the position of the osteosynthesis material is the same. With a deep fracture line, a more cranial positioning of the plate leads to better stabilisation. This study needs to be experimentally validated.