Finite-element-analysis of a six-hole tibia shaft locking plate to optimize the screw hole position

Failures of osteosynthesis plates constitute serious complications. In order to prevent the break of plates it is necessary to analyse their critical stress distribution. In this paper a Finite-Element-Analysis (FEA) is presented for a 6-hole tibia shaft plate. By changing the location of the screws 2 and 5 it was intended to find their optimal position, thus possibly reducing the occurring stresses. Stresses within the implant were analysed using the FEA with the aim to identify the critical areas. For this purpose a bending test was conducted using the FE-Software ANSYS Workbench. A validation of the FEA was performed on a testing machine. To optimize the position of the screws a parameter model was established and the screws 2 and 5 were moved each by 8 mm in both directions. FEA showed that a vertical displacement of 8,3 mm resulted in a maximum stress of 237,36 MPa in the implant. The highest stresses were identified in the plate near the screw holes close to the fracture. Maximum stresses in the screws were found in screw 3 and 4 (185 MPa), located in the transition head/shank. The validation of the FEA showed maximum deviations of 5,09%, occurring in the area of plastic deformation. Variation of the positions for screw 2 and 5 showed no significant reduction of the maximum stresses in the implant. Load transfer happens primarily by the screws 3 and 4 (84%), the screws 2 and 5 transfer 10% and the outer screws 1 and 6 6% of the load. FEA has been shown to be suitable for the provision of reliable parameters regarding the stresses of implants. The results lead to a reduction to 4 screws, which could save costs and reduce operation time. However the mechanical properties of the osteosynthesis plate will be similar and sufficient.