Finite element analysis (FEA) for the Point contact fixator screw drive, plate design, overcuts

Finite Element (FE) analysis was performed to ensure that the newly designed plate for internal fixation, the Point Contact Fixator (PC-Fix), was at least as strong as existing implants used for the same clinical indications. The smaller holes of the PC-Fix allow for some reduction of the cross-sectional dimensions in comparison to a comparable Dynamic Compression Plate. The cross section of the PC-Fix changes along the length in order to provide for point contacts at the level of the screws and to reduce the strength between the holes. These major geometrical characteristics are produced by a longitudinal undercut and a set of transverse undercuts. They are supplemented by shallow cuts on the upper surface of the plate which reduce the effects of bending-induced stress concentration. All of these parameters have been optimized by iterative FE analysis. Equal strength requirement resulted in a modest, but important reduction of the implant size for the critical use in the forearm. In addition, the locking of the conical screw head into the PC-Fix has been analyzed and optimized in order to ensure proper locking of the screw. This has been achieved by a measured geometrical mismatch between the screw head and the hole in the fixator. The maximum compressive stress between the screw head and the fixator, which is considered a critical risk for galling, has been reduced by approximately 50 percent at the required insertion torque.